mm: memcontrol: simplify soft limit tree init code

[cascardo/linux.git] / mm / memcontrol.c

/* memcontrol.c - Memory Controller
 *
 * Copyright IBM Corporation, 2007
 * Author Balbir Singh <balbir@linux.vnet.ibm.com>
 *
 * Copyright 2007 OpenVZ SWsoft Inc
 * Author: Pavel Emelianov <xemul@openvz.org>
 *
 * Memory thresholds
 * Copyright (C) 2009 Nokia Corporation
 * Author: Kirill A. Shutemov
 *
 * Kernel Memory Controller
 * Copyright (C) 2012 Parallels Inc. and Google Inc.
 * Authors: Glauber Costa and Suleiman Souhlal
 *
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 2 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 */

#include <linux/page_counter.h>
#include <linux/memcontrol.h>
#include <linux/cgroup.h>
#include <linux/mm.h>
#include <linux/hugetlb.h>
#include <linux/pagemap.h>
#include <linux/smp.h>
#include <linux/page-flags.h>
#include <linux/backing-dev.h>
#include <linux/bit_spinlock.h>
#include <linux/rcupdate.h>
#include <linux/limits.h>
#include <linux/export.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/slab.h>
#include <linux/swap.h>
#include <linux/swapops.h>
#include <linux/spinlock.h>
#include <linux/eventfd.h>
#include <linux/poll.h>
#include <linux/sort.h>
#include <linux/fs.h>
#include <linux/seq_file.h>
#include <linux/vmpressure.h>
#include <linux/mm_inline.h>
#include <linux/swap_cgroup.h>
#include <linux/cpu.h>
#include <linux/oom.h>
#include <linux/lockdep.h>
#include <linux/file.h>
#include "internal.h"
#include <net/sock.h>
#include <net/ip.h>
#include <net/tcp_memcontrol.h>
#include "slab.h"

#include <asm/uaccess.h>

#include <trace/events/vmscan.h>

struct cgroup_subsys memory_cgrp_subsys __read_mostly;
EXPORT_SYMBOL(memory_cgrp_subsys);

#define MEM_CGROUP_RECLAIM_RETRIES      5
static struct mem_cgroup *root_mem_cgroup __read_mostly;

#ifdef CONFIG_MEMCG_SWAP
/* Turned on only when memory cgroup is enabled && really_do_swap_account = 1 */
int do_swap_account __read_mostly;

/* for remember boot option*/
#ifdef CONFIG_MEMCG_SWAP_ENABLED
static int really_do_swap_account __initdata = 1;
#else
static int really_do_swap_account __initdata;
#endif

#else
#define do_swap_account         0
#endif


static const char * const mem_cgroup_stat_names[] = {
        "cache",
        "rss",
        "rss_huge",
        "mapped_file",
        "writeback",
        "swap",
};

static const char * const mem_cgroup_events_names[] = {
        "pgpgin",
        "pgpgout",
        "pgfault",
        "pgmajfault",
};

static const char * const mem_cgroup_lru_names[] = {
        "inactive_anon",
        "active_anon",
        "inactive_file",
        "active_file",
        "unevictable",
};

/*
 * Per memcg event counter is incremented at every pagein/pageout. With THP,
 * it will be incremated by the number of pages. This counter is used for
 * for trigger some periodic events. This is straightforward and better
 * than using jiffies etc. to handle periodic memcg event.
 */
enum mem_cgroup_events_target {
        MEM_CGROUP_TARGET_THRESH,
        MEM_CGROUP_TARGET_SOFTLIMIT,
        MEM_CGROUP_TARGET_NUMAINFO,
        MEM_CGROUP_NTARGETS,
};
#define THRESHOLDS_EVENTS_TARGET 128
#define SOFTLIMIT_EVENTS_TARGET 1024
#define NUMAINFO_EVENTS_TARGET  1024

struct mem_cgroup_stat_cpu {
        long count[MEM_CGROUP_STAT_NSTATS];
        unsigned long events[MEMCG_NR_EVENTS];
        unsigned long nr_page_events;
        unsigned long targets[MEM_CGROUP_NTARGETS];
};

struct reclaim_iter {
        struct mem_cgroup *position;
        /* scan generation, increased every round-trip */
        unsigned int generation;
};

/*
 * per-zone information in memory controller.
 */
struct mem_cgroup_per_zone {
        struct lruvec           lruvec;
        unsigned long           lru_size[NR_LRU_LISTS];

        struct reclaim_iter     iter[DEF_PRIORITY + 1];

        struct rb_node          tree_node;      /* RB tree node */
        unsigned long           usage_in_excess;/* Set to the value by which */
                                                /* the soft limit is exceeded*/
        bool                    on_tree;
        struct mem_cgroup       *memcg;         /* Back pointer, we cannot */
                                                /* use container_of        */
};

struct mem_cgroup_per_node {
        struct mem_cgroup_per_zone zoneinfo[MAX_NR_ZONES];
};

/*
 * Cgroups above their limits are maintained in a RB-Tree, independent of
 * their hierarchy representation
 */

struct mem_cgroup_tree_per_zone {
        struct rb_root rb_root;
        spinlock_t lock;
};

struct mem_cgroup_tree_per_node {
        struct mem_cgroup_tree_per_zone rb_tree_per_zone[MAX_NR_ZONES];
};

struct mem_cgroup_tree {
        struct mem_cgroup_tree_per_node *rb_tree_per_node[MAX_NUMNODES];
};

static struct mem_cgroup_tree soft_limit_tree __read_mostly;

struct mem_cgroup_threshold {
        struct eventfd_ctx *eventfd;
        unsigned long threshold;
};

/* For threshold */
struct mem_cgroup_threshold_ary {
        /* An array index points to threshold just below or equal to usage. */
        int current_threshold;
        /* Size of entries[] */
        unsigned int size;
        /* Array of thresholds */
        struct mem_cgroup_threshold entries[0];
};

struct mem_cgroup_thresholds {
        /* Primary thresholds array */
        struct mem_cgroup_threshold_ary *primary;
        /*
         * Spare threshold array.
         * This is needed to make mem_cgroup_unregister_event() "never fail".
         * It must be able to store at least primary->size - 1 entries.
         */
        struct mem_cgroup_threshold_ary *spare;
};

/* for OOM */
struct mem_cgroup_eventfd_list {
        struct list_head list;
        struct eventfd_ctx *eventfd;
};

/*
 * cgroup_event represents events which userspace want to receive.
 */
struct mem_cgroup_event {
        /*
         * memcg which the event belongs to.
         */
        struct mem_cgroup *memcg;
        /*
         * eventfd to signal userspace about the event.
         */
        struct eventfd_ctx *eventfd;
        /*
         * Each of these stored in a list by the cgroup.
         */
        struct list_head list;
        /*
         * register_event() callback will be used to add new userspace
         * waiter for changes related to this event.  Use eventfd_signal()
         * on eventfd to send notification to userspace.
         */
        int (*register_event)(struct mem_cgroup *memcg,
                              struct eventfd_ctx *eventfd, const char *args);
        /*
         * unregister_event() callback will be called when userspace closes
         * the eventfd or on cgroup removing.  This callback must be set,
         * if you want provide notification functionality.
         */
        void (*unregister_event)(struct mem_cgroup *memcg,
                                 struct eventfd_ctx *eventfd);
        /*
         * All fields below needed to unregister event when
         * userspace closes eventfd.
         */
        poll_table pt;
        wait_queue_head_t *wqh;
        wait_queue_t wait;
        struct work_struct remove;
};

static void mem_cgroup_threshold(struct mem_cgroup *memcg);
static void mem_cgroup_oom_notify(struct mem_cgroup *memcg);

/*
 * The memory controller data structure. The memory controller controls both
 * page cache and RSS per cgroup. We would eventually like to provide
 * statistics based on the statistics developed by Rik Van Riel for clock-pro,
 * to help the administrator determine what knobs to tune.
 *
 * TODO: Add a water mark for the memory controller. Reclaim will begin when
 * we hit the water mark. May be even add a low water mark, such that
 * no reclaim occurs from a cgroup at it's low water mark, this is
 * a feature that will be implemented much later in the future.
 */
struct mem_cgroup {
        struct cgroup_subsys_state css;

        /* Accounted resources */
        struct page_counter memory;
        struct page_counter memsw;
        struct page_counter kmem;

        /* Normal memory consumption range */
        unsigned long low;
        unsigned long high;

        unsigned long soft_limit;

        /* vmpressure notifications */
        struct vmpressure vmpressure;

        /* css_online() has been completed */
        int initialized;

        /*
         * Should the accounting and control be hierarchical, per subtree?
         */
        bool use_hierarchy;

        bool            oom_lock;
        atomic_t        under_oom;
        atomic_t        oom_wakeups;

        int     swappiness;
        /* OOM-Killer disable */
        int             oom_kill_disable;

        /* protect arrays of thresholds */
        struct mutex thresholds_lock;

        /* thresholds for memory usage. RCU-protected */
        struct mem_cgroup_thresholds thresholds;

        /* thresholds for mem+swap usage. RCU-protected */
        struct mem_cgroup_thresholds memsw_thresholds;

        /* For oom notifier event fd */
        struct list_head oom_notify;

        /*
         * Should we move charges of a task when a task is moved into this
         * mem_cgroup ? And what type of charges should we move ?
         */
        unsigned long move_charge_at_immigrate;
        /*
         * set > 0 if pages under this cgroup are moving to other cgroup.
         */
        atomic_t                moving_account;
        /* taken only while moving_account > 0 */
        spinlock_t              move_lock;
        struct task_struct      *move_lock_task;
        unsigned long           move_lock_flags;
        /*
         * percpu counter.
         */
        struct mem_cgroup_stat_cpu __percpu *stat;
        /*
         * used when a cpu is offlined or other synchronizations
         * See mem_cgroup_read_stat().
         */
        struct mem_cgroup_stat_cpu nocpu_base;
        spinlock_t pcp_counter_lock;

#if defined(CONFIG_MEMCG_KMEM) && defined(CONFIG_INET)
        struct cg_proto tcp_mem;
#endif
#if defined(CONFIG_MEMCG_KMEM)
        /* Index in the kmem_cache->memcg_params->memcg_caches array */
        int kmemcg_id;
#endif

        int last_scanned_node;
#if MAX_NUMNODES > 1
        nodemask_t      scan_nodes;
        atomic_t        numainfo_events;
        atomic_t        numainfo_updating;
#endif

        /* List of events which userspace want to receive */
        struct list_head event_list;
        spinlock_t event_list_lock;

        struct mem_cgroup_per_node *nodeinfo[0];
        /* WARNING: nodeinfo must be the last member here */
};

#ifdef CONFIG_MEMCG_KMEM
static bool memcg_kmem_is_active(struct mem_cgroup *memcg)
{
        return memcg->kmemcg_id >= 0;
}
#endif

/* Stuffs for move charges at task migration. */
/*
 * Types of charges to be moved.
 */
#define MOVE_ANON       0x1U
#define MOVE_FILE       0x2U
#define MOVE_MASK       (MOVE_ANON | MOVE_FILE)

/* "mc" and its members are protected by cgroup_mutex */
static struct move_charge_struct {
        spinlock_t        lock; /* for from, to */
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        unsigned long flags;
        unsigned long precharge;
        unsigned long moved_charge;
        unsigned long moved_swap;
        struct task_struct *moving_task;        /* a task moving charges */
        wait_queue_head_t waitq;                /* a waitq for other context */
} mc = {
        .lock = __SPIN_LOCK_UNLOCKED(mc.lock),
        .waitq = __WAIT_QUEUE_HEAD_INITIALIZER(mc.waitq),
};

/*
 * Maximum loops in mem_cgroup_hierarchical_reclaim(), used for soft
 * limit reclaim to prevent infinite loops, if they ever occur.
 */
#define MEM_CGROUP_MAX_RECLAIM_LOOPS            100
#define MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS 2

enum charge_type {
        MEM_CGROUP_CHARGE_TYPE_CACHE = 0,
        MEM_CGROUP_CHARGE_TYPE_ANON,
        MEM_CGROUP_CHARGE_TYPE_SWAPOUT, /* for accounting swapcache */
        MEM_CGROUP_CHARGE_TYPE_DROP,    /* a page was unused swap cache */
        NR_CHARGE_TYPE,
};

/* for encoding cft->private value on file */
enum res_type {
        _MEM,
        _MEMSWAP,
        _OOM_TYPE,
        _KMEM,
};

#define MEMFILE_PRIVATE(x, val) ((x) << 16 | (val))
#define MEMFILE_TYPE(val)       ((val) >> 16 & 0xffff)
#define MEMFILE_ATTR(val)       ((val) & 0xffff)
/* Used for OOM nofiier */
#define OOM_CONTROL             (0)

/*
 * The memcg_create_mutex will be held whenever a new cgroup is created.
 * As a consequence, any change that needs to protect against new child cgroups
 * appearing has to hold it as well.
 */
static DEFINE_MUTEX(memcg_create_mutex);

struct mem_cgroup *mem_cgroup_from_css(struct cgroup_subsys_state *s)
{
        return s ? container_of(s, struct mem_cgroup, css) : NULL;
}

/* Some nice accessors for the vmpressure. */
struct vmpressure *memcg_to_vmpressure(struct mem_cgroup *memcg)
{
        if (!memcg)
                memcg = root_mem_cgroup;
        return &memcg->vmpressure;
}

struct cgroup_subsys_state *vmpressure_to_css(struct vmpressure *vmpr)
{
        return &container_of(vmpr, struct mem_cgroup, vmpressure)->css;
}

static inline bool mem_cgroup_is_root(struct mem_cgroup *memcg)
{
        return (memcg == root_mem_cgroup);
}

/*
 * We restrict the id in the range of [1, 65535], so it can fit into
 * an unsigned short.
 */
#define MEM_CGROUP_ID_MAX       USHRT_MAX

static inline unsigned short mem_cgroup_id(struct mem_cgroup *memcg)
{
        return memcg->css.id;
}

static inline struct mem_cgroup *mem_cgroup_from_id(unsigned short id)
{
        struct cgroup_subsys_state *css;

        css = css_from_id(id, &memory_cgrp_subsys);
        return mem_cgroup_from_css(css);
}

/* Writing them here to avoid exposing memcg's inner layout */
#if defined(CONFIG_INET) && defined(CONFIG_MEMCG_KMEM)

void sock_update_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled) {
                struct mem_cgroup *memcg;
                struct cg_proto *cg_proto;

                BUG_ON(!sk->sk_prot->proto_cgroup);

                /* Socket cloning can throw us here with sk_cgrp already
                 * filled. It won't however, necessarily happen from
                 * process context. So the test for root memcg given
                 * the current task's memcg won't help us in this case.
                 *
                 * Respecting the original socket's memcg is a better
                 * decision in this case.
                 */
                if (sk->sk_cgrp) {
                        BUG_ON(mem_cgroup_is_root(sk->sk_cgrp->memcg));
                        css_get(&sk->sk_cgrp->memcg->css);
                        return;
                }

                rcu_read_lock();
                memcg = mem_cgroup_from_task(current);
                cg_proto = sk->sk_prot->proto_cgroup(memcg);
                if (!mem_cgroup_is_root(memcg) &&
                    memcg_proto_active(cg_proto) &&
                    css_tryget_online(&memcg->css)) {
                        sk->sk_cgrp = cg_proto;
                }
                rcu_read_unlock();
        }
}
EXPORT_SYMBOL(sock_update_memcg);

void sock_release_memcg(struct sock *sk)
{
        if (mem_cgroup_sockets_enabled && sk->sk_cgrp) {
                struct mem_cgroup *memcg;
                WARN_ON(!sk->sk_cgrp->memcg);
                memcg = sk->sk_cgrp->memcg;
                css_put(&sk->sk_cgrp->memcg->css);
        }
}

struct cg_proto *tcp_proto_cgroup(struct mem_cgroup *memcg)
{
        if (!memcg || mem_cgroup_is_root(memcg))
                return NULL;

        return &memcg->tcp_mem;
}
EXPORT_SYMBOL(tcp_proto_cgroup);

static void disarm_sock_keys(struct mem_cgroup *memcg)
{
        if (!memcg_proto_activated(&memcg->tcp_mem))
                return;
        static_key_slow_dec(&memcg_socket_limit_enabled);
}
#else
static void disarm_sock_keys(struct mem_cgroup *memcg)
{
}
#endif

#ifdef CONFIG_MEMCG_KMEM
/*
 * This will be the memcg's index in each cache's ->memcg_params->memcg_caches.
 * The main reason for not using cgroup id for this:
 *  this works better in sparse environments, where we have a lot of memcgs,
 *  but only a few kmem-limited. Or also, if we have, for instance, 200
 *  memcgs, and none but the 200th is kmem-limited, we'd have to have a
 *  200 entry array for that.
 *
 * The current size of the caches array is stored in
 * memcg_limited_groups_array_size.  It will double each time we have to
 * increase it.
 */
static DEFINE_IDA(kmem_limited_groups);
int memcg_limited_groups_array_size;

/*
 * MIN_SIZE is different than 1, because we would like to avoid going through
 * the alloc/free process all the time. In a small machine, 4 kmem-limited
 * cgroups is a reasonable guess. In the future, it could be a parameter or
 * tunable, but that is strictly not necessary.
 *
 * MAX_SIZE should be as large as the number of cgrp_ids. Ideally, we could get
 * this constant directly from cgroup, but it is understandable that this is
 * better kept as an internal representation in cgroup.c. In any case, the
 * cgrp_id space is not getting any smaller, and we don't have to necessarily
 * increase ours as well if it increases.
 */
#define MEMCG_CACHES_MIN_SIZE 4
#define MEMCG_CACHES_MAX_SIZE MEM_CGROUP_ID_MAX

/*
 * A lot of the calls to the cache allocation functions are expected to be
 * inlined by the compiler. Since the calls to memcg_kmem_get_cache are
 * conditional to this static branch, we'll have to allow modules that does
 * kmem_cache_alloc and the such to see this symbol as well
 */
struct static_key memcg_kmem_enabled_key;
EXPORT_SYMBOL(memcg_kmem_enabled_key);

static void memcg_free_cache_id(int id);

static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
        if (memcg_kmem_is_active(memcg)) {
                static_key_slow_dec(&memcg_kmem_enabled_key);
                memcg_free_cache_id(memcg->kmemcg_id);
        }
        /*
         * This check can't live in kmem destruction function,
         * since the charges will outlive the cgroup
         */
        WARN_ON(page_counter_read(&memcg->kmem));
}
#else
static void disarm_kmem_keys(struct mem_cgroup *memcg)
{
}
#endif /* CONFIG_MEMCG_KMEM */

static void disarm_static_keys(struct mem_cgroup *memcg)
{
        disarm_sock_keys(memcg);
        disarm_kmem_keys(memcg);
}

static struct mem_cgroup_per_zone *
mem_cgroup_zone_zoneinfo(struct mem_cgroup *memcg, struct zone *zone)
{
        int nid = zone_to_nid(zone);
        int zid = zone_idx(zone);

        return &memcg->nodeinfo[nid]->zoneinfo[zid];
}

struct cgroup_subsys_state *mem_cgroup_css(struct mem_cgroup *memcg)
{
        return &memcg->css;
}

static struct mem_cgroup_per_zone *
mem_cgroup_page_zoneinfo(struct mem_cgroup *memcg, struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return &memcg->nodeinfo[nid]->zoneinfo[zid];
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_node_zone(int nid, int zid)
{
        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static struct mem_cgroup_tree_per_zone *
soft_limit_tree_from_page(struct page *page)
{
        int nid = page_to_nid(page);
        int zid = page_zonenum(page);

        return &soft_limit_tree.rb_tree_per_node[nid]->rb_tree_per_zone[zid];
}

static void __mem_cgroup_insert_exceeded(struct mem_cgroup_per_zone *mz,
                                         struct mem_cgroup_tree_per_zone *mctz,
                                         unsigned long new_usage_in_excess)
{
        struct rb_node **p = &mctz->rb_root.rb_node;
        struct rb_node *parent = NULL;
        struct mem_cgroup_per_zone *mz_node;

        if (mz->on_tree)
                return;

        mz->usage_in_excess = new_usage_in_excess;
        if (!mz->usage_in_excess)
                return;
        while (*p) {
                parent = *p;
                mz_node = rb_entry(parent, struct mem_cgroup_per_zone,
                                        tree_node);
                if (mz->usage_in_excess < mz_node->usage_in_excess)
                        p = &(*p)->rb_left;
                /*
                 * We can't avoid mem cgroups that are over their soft
                 * limit by the same amount
                 */
                else if (mz->usage_in_excess >= mz_node->usage_in_excess)
                        p = &(*p)->rb_right;
        }
        rb_link_node(&mz->tree_node, parent, p);
        rb_insert_color(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = true;
}

static void __mem_cgroup_remove_exceeded(struct mem_cgroup_per_zone *mz,
                                         struct mem_cgroup_tree_per_zone *mctz)
{
        if (!mz->on_tree)
                return;
        rb_erase(&mz->tree_node, &mctz->rb_root);
        mz->on_tree = false;
}

static void mem_cgroup_remove_exceeded(struct mem_cgroup_per_zone *mz,
                                       struct mem_cgroup_tree_per_zone *mctz)
{
        unsigned long flags;

        spin_lock_irqsave(&mctz->lock, flags);
        __mem_cgroup_remove_exceeded(mz, mctz);
        spin_unlock_irqrestore(&mctz->lock, flags);
}

static unsigned long soft_limit_excess(struct mem_cgroup *memcg)
{
        unsigned long nr_pages = page_counter_read(&memcg->memory);
        unsigned long soft_limit = ACCESS_ONCE(memcg->soft_limit);
        unsigned long excess = 0;

        if (nr_pages > soft_limit)
                excess = nr_pages - soft_limit;

        return excess;
}

static void mem_cgroup_update_tree(struct mem_cgroup *memcg, struct page *page)
{
        unsigned long excess;
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup_tree_per_zone *mctz;

        mctz = soft_limit_tree_from_page(page);
        /*
         * Necessary to update all ancestors when hierarchy is used.
         * because their event counter is not touched.
         */
        for (; memcg; memcg = parent_mem_cgroup(memcg)) {
                mz = mem_cgroup_page_zoneinfo(memcg, page);
                excess = soft_limit_excess(memcg);
                /*
                 * We have to update the tree if mz is on RB-tree or
                 * mem is over its softlimit.
                 */
                if (excess || mz->on_tree) {
                        unsigned long flags;

                        spin_lock_irqsave(&mctz->lock, flags);
                        /* if on-tree, remove it */
                        if (mz->on_tree)
                                __mem_cgroup_remove_exceeded(mz, mctz);
                        /*
                         * Insert again. mz->usage_in_excess will be updated.
                         * If excess is 0, no tree ops.
                         */
                        __mem_cgroup_insert_exceeded(mz, mctz, excess);
                        spin_unlock_irqrestore(&mctz->lock, flags);
                }
        }
}

static void mem_cgroup_remove_from_trees(struct mem_cgroup *memcg)
{
        struct mem_cgroup_tree_per_zone *mctz;
        struct mem_cgroup_per_zone *mz;
        int nid, zid;

        for_each_node(nid) {
                for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                        mz = &memcg->nodeinfo[nid]->zoneinfo[zid];
                        mctz = soft_limit_tree_node_zone(nid, zid);
                        mem_cgroup_remove_exceeded(mz, mctz);
                }
        }
}

static struct mem_cgroup_per_zone *
__mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct rb_node *rightmost = NULL;
        struct mem_cgroup_per_zone *mz;

retry:
        mz = NULL;
        rightmost = rb_last(&mctz->rb_root);
        if (!rightmost)
                goto done;              /* Nothing to reclaim from */

        mz = rb_entry(rightmost, struct mem_cgroup_per_zone, tree_node);
        /*
         * Remove the node now but someone else can add it back,
         * we will to add it back at the end of reclaim to its correct
         * position in the tree.
         */
        __mem_cgroup_remove_exceeded(mz, mctz);
        if (!soft_limit_excess(mz->memcg) ||
            !css_tryget_online(&mz->memcg->css))
                goto retry;
done:
        return mz;
}

static struct mem_cgroup_per_zone *
mem_cgroup_largest_soft_limit_node(struct mem_cgroup_tree_per_zone *mctz)
{
        struct mem_cgroup_per_zone *mz;

        spin_lock_irq(&mctz->lock);
        mz = __mem_cgroup_largest_soft_limit_node(mctz);
        spin_unlock_irq(&mctz->lock);
        return mz;
}

/*
 * Implementation Note: reading percpu statistics for memcg.
 *
 * Both of vmstat[] and percpu_counter has threshold and do periodic
 * synchronization to implement "quick" read. There are trade-off between
 * reading cost and precision of value. Then, we may have a chance to implement
 * a periodic synchronizion of counter in memcg's counter.
 *
 * But this _read() function is used for user interface now. The user accounts
 * memory usage by memory cgroup and he _always_ requires exact value because
 * he accounts memory. Even if we provide quick-and-fuzzy read, we always
 * have to visit all online cpus and make sum. So, for now, unnecessary
 * synchronization is not implemented. (just implemented for cpu hotplug)
 *
 * If there are kernel internal actions which can make use of some not-exact
 * value, and reading all cpu value can be performance bottleneck in some
 * common workload, threashold and synchonization as vmstat[] should be
 * implemented.
 */
static long mem_cgroup_read_stat(struct mem_cgroup *memcg,
                                 enum mem_cgroup_stat_index idx)
{
        long val = 0;
        int cpu;

        get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->count[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.count[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        put_online_cpus();
        return val;
}

static unsigned long mem_cgroup_read_events(struct mem_cgroup *memcg,
                                            enum mem_cgroup_events_index idx)
{
        unsigned long val = 0;
        int cpu;

        get_online_cpus();
        for_each_online_cpu(cpu)
                val += per_cpu(memcg->stat->events[idx], cpu);
#ifdef CONFIG_HOTPLUG_CPU
        spin_lock(&memcg->pcp_counter_lock);
        val += memcg->nocpu_base.events[idx];
        spin_unlock(&memcg->pcp_counter_lock);
#endif
        put_online_cpus();
        return val;
}

static void mem_cgroup_charge_statistics(struct mem_cgroup *memcg,
                                         struct page *page,
                                         int nr_pages)
{
        /*
         * Here, RSS means 'mapped anon' and anon's SwapCache. Shmem/tmpfs is
         * counted as CACHE even if it's on ANON LRU.
         */
        if (PageAnon(page))
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS],
                                nr_pages);
        else
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_CACHE],
                                nr_pages);

        if (PageTransHuge(page))
                __this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
                                nr_pages);

        /* pagein of a big page is an event. So, ignore page size */
        if (nr_pages > 0)
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGIN]);
        else {
                __this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGOUT]);
                nr_pages = -nr_pages; /* for event */
        }

        __this_cpu_add(memcg->stat->nr_page_events, nr_pages);
}

unsigned long mem_cgroup_get_lru_size(struct lruvec *lruvec, enum lru_list lru)
{
        struct mem_cgroup_per_zone *mz;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        return mz->lru_size[lru];
}

static unsigned long mem_cgroup_node_nr_lru_pages(struct mem_cgroup *memcg,
                                                  int nid,
                                                  unsigned int lru_mask)
{
        unsigned long nr = 0;
        int zid;

        VM_BUG_ON((unsigned)nid >= nr_node_ids);

        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                struct mem_cgroup_per_zone *mz;
                enum lru_list lru;

                for_each_lru(lru) {
                        if (!(BIT(lru) & lru_mask))
                                continue;
                        mz = &memcg->nodeinfo[nid]->zoneinfo[zid];
                        nr += mz->lru_size[lru];
                }
        }
        return nr;
}

static unsigned long mem_cgroup_nr_lru_pages(struct mem_cgroup *memcg,
                        unsigned int lru_mask)
{
        unsigned long nr = 0;
        int nid;

        for_each_node_state(nid, N_MEMORY)
                nr += mem_cgroup_node_nr_lru_pages(memcg, nid, lru_mask);
        return nr;
}

static bool mem_cgroup_event_ratelimit(struct mem_cgroup *memcg,
                                       enum mem_cgroup_events_target target)
{
        unsigned long val, next;

        val = __this_cpu_read(memcg->stat->nr_page_events);
        next = __this_cpu_read(memcg->stat->targets[target]);
        /* from time_after() in jiffies.h */
        if ((long)next - (long)val < 0) {
                switch (target) {
                case MEM_CGROUP_TARGET_THRESH:
                        next = val + THRESHOLDS_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_SOFTLIMIT:
                        next = val + SOFTLIMIT_EVENTS_TARGET;
                        break;
                case MEM_CGROUP_TARGET_NUMAINFO:
                        next = val + NUMAINFO_EVENTS_TARGET;
                        break;
                default:
                        break;
                }
                __this_cpu_write(memcg->stat->targets[target], next);
                return true;
        }
        return false;
}

/*
 * Check events in order.
 *
 */
static void memcg_check_events(struct mem_cgroup *memcg, struct page *page)
{
        /* threshold event is triggered in finer grain than soft limit */
        if (unlikely(mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_THRESH))) {
                bool do_softlimit;
                bool do_numainfo __maybe_unused;

                do_softlimit = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_SOFTLIMIT);
#if MAX_NUMNODES > 1
                do_numainfo = mem_cgroup_event_ratelimit(memcg,
                                                MEM_CGROUP_TARGET_NUMAINFO);
#endif
                mem_cgroup_threshold(memcg);
                if (unlikely(do_softlimit))
                        mem_cgroup_update_tree(memcg, page);
#if MAX_NUMNODES > 1
                if (unlikely(do_numainfo))
                        atomic_inc(&memcg->numainfo_events);
#endif
        }
}

struct mem_cgroup *mem_cgroup_from_task(struct task_struct *p)
{
        /*
         * mm_update_next_owner() may clear mm->owner to NULL
         * if it races with swapoff, page migration, etc.
         * So this can be called with p == NULL.
         */
        if (unlikely(!p))
                return NULL;

        return mem_cgroup_from_css(task_css(p, memory_cgrp_id));
}

static struct mem_cgroup *get_mem_cgroup_from_mm(struct mm_struct *mm)
{
        struct mem_cgroup *memcg = NULL;

        rcu_read_lock();
        do {
                /*
                 * Page cache insertions can happen withou an
                 * actual mm context, e.g. during disk probing
                 * on boot, loopback IO, acct() writes etc.
                 */
                if (unlikely(!mm))
                        memcg = root_mem_cgroup;
                else {
                        memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
                        if (unlikely(!memcg))
                                memcg = root_mem_cgroup;
                }
        } while (!css_tryget_online(&memcg->css));
        rcu_read_unlock();
        return memcg;
}

/**
 * mem_cgroup_iter - iterate over memory cgroup hierarchy
 * @root: hierarchy root
 * @prev: previously returned memcg, NULL on first invocation
 * @reclaim: cookie for shared reclaim walks, NULL for full walks
 *
 * Returns references to children of the hierarchy below @root, or
 * @root itself, or %NULL after a full round-trip.
 *
 * Caller must pass the return value in @prev on subsequent
 * invocations for reference counting, or use mem_cgroup_iter_break()
 * to cancel a hierarchy walk before the round-trip is complete.
 *
 * Reclaimers can specify a zone and a priority level in @reclaim to
 * divide up the memcgs in the hierarchy among all concurrent
 * reclaimers operating on the same zone and priority.
 */
struct mem_cgroup *mem_cgroup_iter(struct mem_cgroup *root,
                                   struct mem_cgroup *prev,
                                   struct mem_cgroup_reclaim_cookie *reclaim)
{
        struct reclaim_iter *uninitialized_var(iter);
        struct cgroup_subsys_state *css = NULL;
        struct mem_cgroup *memcg = NULL;
        struct mem_cgroup *pos = NULL;

        if (mem_cgroup_disabled())
                return NULL;

        if (!root)
                root = root_mem_cgroup;

        if (prev && !reclaim)
                pos = prev;

        if (!root->use_hierarchy && root != root_mem_cgroup) {
                if (prev)
                        goto out;
                return root;
        }

        rcu_read_lock();

        if (reclaim) {
                struct mem_cgroup_per_zone *mz;

                mz = mem_cgroup_zone_zoneinfo(root, reclaim->zone);
                iter = &mz->iter[reclaim->priority];

                if (prev && reclaim->generation != iter->generation)
                        goto out_unlock;

                do {
                        pos = ACCESS_ONCE(iter->position);
                        /*
                         * A racing update may change the position and
                         * put the last reference, hence css_tryget(),
                         * or retry to see the updated position.
                         */
                } while (pos && !css_tryget(&pos->css));
        }

        if (pos)
                css = &pos->css;

        for (;;) {
                css = css_next_descendant_pre(css, &root->css);
                if (!css) {
                        /*
                         * Reclaimers share the hierarchy walk, and a
                         * new one might jump in right at the end of
                         * the hierarchy - make sure they see at least
                         * one group and restart from the beginning.
                         */
                        if (!prev)
                                continue;
                        break;
                }

                /*
                 * Verify the css and acquire a reference.  The root
                 * is provided by the caller, so we know it's alive
                 * and kicking, and don't take an extra reference.
                 */
                memcg = mem_cgroup_from_css(css);

                if (css == &root->css)
                        break;

                if (css_tryget(css)) {
                        /*
                         * Make sure the memcg is initialized:
                         * mem_cgroup_css_online() orders the the
                         * initialization against setting the flag.
                         */
                        if (smp_load_acquire(&memcg->initialized))
                                break;

                        css_put(css);
                }

                memcg = NULL;
        }

        if (reclaim) {
                if (cmpxchg(&iter->position, pos, memcg) == pos) {
                        if (memcg)
                                css_get(&memcg->css);
                        if (pos)
                                css_put(&pos->css);
                }

                /*
                 * pairs with css_tryget when dereferencing iter->position
                 * above.
                 */
                if (pos)
                        css_put(&pos->css);

                if (!memcg)
                        iter->generation++;
                else if (!prev)
                        reclaim->generation = iter->generation;
        }

out_unlock:
        rcu_read_unlock();
out:
        if (prev && prev != root)
                css_put(&prev->css);

        return memcg;
}

/**
 * mem_cgroup_iter_break - abort a hierarchy walk prematurely
 * @root: hierarchy root
 * @prev: last visited hierarchy member as returned by mem_cgroup_iter()
 */
void mem_cgroup_iter_break(struct mem_cgroup *root,
                           struct mem_cgroup *prev)
{
        if (!root)
                root = root_mem_cgroup;
        if (prev && prev != root)
                css_put(&prev->css);
}

/*
 * Iteration constructs for visiting all cgroups (under a tree).  If
 * loops are exited prematurely (break), mem_cgroup_iter_break() must
 * be used for reference counting.
 */
#define for_each_mem_cgroup_tree(iter, root)            \
        for (iter = mem_cgroup_iter(root, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(root, iter, NULL))

#define for_each_mem_cgroup(iter)                       \
        for (iter = mem_cgroup_iter(NULL, NULL, NULL);  \
             iter != NULL;                              \
             iter = mem_cgroup_iter(NULL, iter, NULL))

void __mem_cgroup_count_vm_event(struct mm_struct *mm, enum vm_event_item idx)
{
        struct mem_cgroup *memcg;

        rcu_read_lock();
        memcg = mem_cgroup_from_task(rcu_dereference(mm->owner));
        if (unlikely(!memcg))
                goto out;

        switch (idx) {
        case PGFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGFAULT]);
                break;
        case PGMAJFAULT:
                this_cpu_inc(memcg->stat->events[MEM_CGROUP_EVENTS_PGMAJFAULT]);
                break;
        default:
                BUG();
        }
out:
        rcu_read_unlock();
}
EXPORT_SYMBOL(__mem_cgroup_count_vm_event);

/**
 * mem_cgroup_zone_lruvec - get the lru list vector for a zone and memcg
 * @zone: zone of the wanted lruvec
 * @memcg: memcg of the wanted lruvec
 *
 * Returns the lru list vector holding pages for the given @zone and
 * @mem.  This can be the global zone lruvec, if the memory controller
 * is disabled.
 */
struct lruvec *mem_cgroup_zone_lruvec(struct zone *zone,
                                      struct mem_cgroup *memcg)
{
        struct mem_cgroup_per_zone *mz;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        mz = mem_cgroup_zone_zoneinfo(memcg, zone);
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/**
 * mem_cgroup_page_lruvec - return lruvec for isolating/putting an LRU page
 * @page: the page
 * @zone: zone of the page
 *
 * This function is only safe when following the LRU page isolation
 * and putback protocol: the LRU lock must be held, and the page must
 * either be PageLRU() or the caller must have isolated/allocated it.
 */
struct lruvec *mem_cgroup_page_lruvec(struct page *page, struct zone *zone)
{
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup *memcg;
        struct lruvec *lruvec;

        if (mem_cgroup_disabled()) {
                lruvec = &zone->lruvec;
                goto out;
        }

        memcg = page->mem_cgroup;
        /*
         * Swapcache readahead pages are added to the LRU - and
         * possibly migrated - before they are charged.
         */
        if (!memcg)
                memcg = root_mem_cgroup;

        mz = mem_cgroup_page_zoneinfo(memcg, page);
        lruvec = &mz->lruvec;
out:
        /*
         * Since a node can be onlined after the mem_cgroup was created,
         * we have to be prepared to initialize lruvec->zone here;
         * and if offlined then reonlined, we need to reinitialize it.
         */
        if (unlikely(lruvec->zone != zone))
                lruvec->zone = zone;
        return lruvec;
}

/**
 * mem_cgroup_update_lru_size - account for adding or removing an lru page
 * @lruvec: mem_cgroup per zone lru vector
 * @lru: index of lru list the page is sitting on
 * @nr_pages: positive when adding or negative when removing
 *
 * This function must be called when a page is added to or removed from an
 * lru list.
 */
void mem_cgroup_update_lru_size(struct lruvec *lruvec, enum lru_list lru,
                                int nr_pages)
{
        struct mem_cgroup_per_zone *mz;
        unsigned long *lru_size;

        if (mem_cgroup_disabled())
                return;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        lru_size = mz->lru_size + lru;
        *lru_size += nr_pages;
        VM_BUG_ON((long)(*lru_size) < 0);
}

bool mem_cgroup_is_descendant(struct mem_cgroup *memcg, struct mem_cgroup *root)
{
        if (root == memcg)
                return true;
        if (!root->use_hierarchy)
                return false;
        return cgroup_is_descendant(memcg->css.cgroup, root->css.cgroup);
}

bool task_in_mem_cgroup(struct task_struct *task, struct mem_cgroup *memcg)
{
        struct mem_cgroup *task_memcg;
        struct task_struct *p;
        bool ret;

        p = find_lock_task_mm(task);
        if (p) {
                task_memcg = get_mem_cgroup_from_mm(p->mm);
                task_unlock(p);
        } else {
                /*
                 * All threads may have already detached their mm's, but the oom
                 * killer still needs to detect if they have already been oom
                 * killed to prevent needlessly killing additional tasks.
                 */
                rcu_read_lock();
                task_memcg = mem_cgroup_from_task(task);
                css_get(&task_memcg->css);
                rcu_read_unlock();
        }
        ret = mem_cgroup_is_descendant(task_memcg, memcg);
        css_put(&task_memcg->css);
        return ret;
}

int mem_cgroup_inactive_anon_is_low(struct lruvec *lruvec)
{
        unsigned long inactive_ratio;
        unsigned long inactive;
        unsigned long active;
        unsigned long gb;

        inactive = mem_cgroup_get_lru_size(lruvec, LRU_INACTIVE_ANON);
        active = mem_cgroup_get_lru_size(lruvec, LRU_ACTIVE_ANON);

        gb = (inactive + active) >> (30 - PAGE_SHIFT);
        if (gb)
                inactive_ratio = int_sqrt(10 * gb);
        else
                inactive_ratio = 1;

        return inactive * inactive_ratio < active;
}

bool mem_cgroup_lruvec_online(struct lruvec *lruvec)
{
        struct mem_cgroup_per_zone *mz;
        struct mem_cgroup *memcg;

        if (mem_cgroup_disabled())
                return true;

        mz = container_of(lruvec, struct mem_cgroup_per_zone, lruvec);
        memcg = mz->memcg;

        return !!(memcg->css.flags & CSS_ONLINE);
}

#define mem_cgroup_from_counter(counter, member)        \
        container_of(counter, struct mem_cgroup, member)

/**
 * mem_cgroup_margin - calculate chargeable space of a memory cgroup
 * @memcg: the memory cgroup
 *
 * Returns the maximum amount of memory @mem can be charged with, in
 * pages.
 */
static unsigned long mem_cgroup_margin(struct mem_cgroup *memcg)
{
        unsigned long margin = 0;
        unsigned long count;
        unsigned long limit;

        count = page_counter_read(&memcg->memory);
        limit = ACCESS_ONCE(memcg->memory.limit);
        if (count < limit)
                margin = limit - count;

        if (do_swap_account) {
                count = page_counter_read(&memcg->memsw);
                limit = ACCESS_ONCE(memcg->memsw.limit);
                if (count <= limit)
                        margin = min(margin, limit - count);
        }

        return margin;
}

int mem_cgroup_swappiness(struct mem_cgroup *memcg)
{
        /* root ? */
        if (mem_cgroup_disabled() || !memcg->css.parent)
                return vm_swappiness;

        return memcg->swappiness;
}

/*
 * A routine for checking "mem" is under move_account() or not.
 *
 * Checking a cgroup is mc.from or mc.to or under hierarchy of
 * moving cgroups. This is for waiting at high-memory pressure
 * caused by "move".
 */
static bool mem_cgroup_under_move(struct mem_cgroup *memcg)
{
        struct mem_cgroup *from;
        struct mem_cgroup *to;
        bool ret = false;
        /*
         * Unlike task_move routines, we access mc.to, mc.from not under
         * mutual exclusion by cgroup_mutex. Here, we take spinlock instead.
         */
        spin_lock(&mc.lock);
        from = mc.from;
        to = mc.to;
        if (!from)
                goto unlock;

        ret = mem_cgroup_is_descendant(from, memcg) ||
                mem_cgroup_is_descendant(to, memcg);
unlock:
        spin_unlock(&mc.lock);
        return ret;
}

static bool mem_cgroup_wait_acct_move(struct mem_cgroup *memcg)
{
        if (mc.moving_task && current != mc.moving_task) {
                if (mem_cgroup_under_move(memcg)) {
                        DEFINE_WAIT(wait);
                        prepare_to_wait(&mc.waitq, &wait, TASK_INTERRUPTIBLE);
                        /* moving charge context might have finished. */
                        if (mc.moving_task)
                                schedule();
                        finish_wait(&mc.waitq, &wait);
                        return true;
                }
        }
        return false;
}

#define K(x) ((x) << (PAGE_SHIFT-10))
/**
 * mem_cgroup_print_oom_info: Print OOM information relevant to memory controller.
 * @memcg: The memory cgroup that went over limit
 * @p: Task that is going to be killed
 *
 * NOTE: @memcg and @p's mem_cgroup can be different when hierarchy is
 * enabled
 */
void mem_cgroup_print_oom_info(struct mem_cgroup *memcg, struct task_struct *p)
{
        /* oom_info_lock ensures that parallel ooms do not interleave */
        static DEFINE_MUTEX(oom_info_lock);
        struct mem_cgroup *iter;
        unsigned int i;

        if (!p)
                return;

        mutex_lock(&oom_info_lock);
        rcu_read_lock();

        pr_info("Task in ");
        pr_cont_cgroup_path(task_cgroup(p, memory_cgrp_id));
        pr_cont(" killed as a result of limit of ");
        pr_cont_cgroup_path(memcg->css.cgroup);
        pr_cont("\n");

        rcu_read_unlock();

        pr_info("memory: usage %llukB, limit %llukB, failcnt %lu\n",
                K((u64)page_counter_read(&memcg->memory)),
                K((u64)memcg->memory.limit), memcg->memory.failcnt);
        pr_info("memory+swap: usage %llukB, limit %llukB, failcnt %lu\n",
                K((u64)page_counter_read(&memcg->memsw)),
                K((u64)memcg->memsw.limit), memcg->memsw.failcnt);
        pr_info("kmem: usage %llukB, limit %llukB, failcnt %lu\n",
                K((u64)page_counter_read(&memcg->kmem)),
                K((u64)memcg->kmem.limit), memcg->kmem.failcnt);

        for_each_mem_cgroup_tree(iter, memcg) {
                pr_info("Memory cgroup stats for ");
                pr_cont_cgroup_path(iter->css.cgroup);
                pr_cont(":");

                for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                        if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                                continue;
                        pr_cont(" %s:%ldKB", mem_cgroup_stat_names[i],
                                K(mem_cgroup_read_stat(iter, i)));
                }

                for (i = 0; i < NR_LRU_LISTS; i++)
                        pr_cont(" %s:%luKB", mem_cgroup_lru_names[i],
                                K(mem_cgroup_nr_lru_pages(iter, BIT(i))));

                pr_cont("\n");
        }
        mutex_unlock(&oom_info_lock);
}

/*
 * This function returns the number of memcg under hierarchy tree. Returns
 * 1(self count) if no children.
 */
static int mem_cgroup_count_children(struct mem_cgroup *memcg)
{
        int num = 0;
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                num++;
        return num;
}

/*
 * Return the memory (and swap, if configured) limit for a memcg.
 */
static unsigned long mem_cgroup_get_limit(struct mem_cgroup *memcg)
{
        unsigned long limit;

        limit = memcg->memory.limit;
        if (mem_cgroup_swappiness(memcg)) {
                unsigned long memsw_limit;

                memsw_limit = memcg->memsw.limit;
                limit = min(limit + total_swap_pages, memsw_limit);
        }
        return limit;
}

static void mem_cgroup_out_of_memory(struct mem_cgroup *memcg, gfp_t gfp_mask,
                                     int order)
{
        struct mem_cgroup *iter;
        unsigned long chosen_points = 0;
        unsigned long totalpages;
        unsigned int points = 0;
        struct task_struct *chosen = NULL;

        /*
         * If current has a pending SIGKILL or is exiting, then automatically
         * select it.  The goal is to allow it to allocate so that it may
         * quickly exit and free its memory.
         */
        if (fatal_signal_pending(current) || task_will_free_mem(current)) {
                mark_tsk_oom_victim(current);
                return;
        }

        check_panic_on_oom(CONSTRAINT_MEMCG, gfp_mask, order, NULL);
        totalpages = mem_cgroup_get_limit(memcg) ? : 1;
        for_each_mem_cgroup_tree(iter, memcg) {
                struct css_task_iter it;
                struct task_struct *task;

                css_task_iter_start(&iter->css, &it);
                while ((task = css_task_iter_next(&it))) {
                        switch (oom_scan_process_thread(task, totalpages, NULL,
                                                        false)) {
                        case OOM_SCAN_SELECT:
                                if (chosen)
                                        put_task_struct(chosen);
                                chosen = task;
                                chosen_points = ULONG_MAX;
                                get_task_struct(chosen);
                                /* fall through */
                        case OOM_SCAN_CONTINUE:
                                continue;
                        case OOM_SCAN_ABORT:
                                css_task_iter_end(&it);
                                mem_cgroup_iter_break(memcg, iter);
                                if (chosen)
                                        put_task_struct(chosen);
                                return;
                        case OOM_SCAN_OK:
                                break;
                        };
                        points = oom_badness(task, memcg, NULL, totalpages);
                        if (!points || points < chosen_points)
                                continue;
                        /* Prefer thread group leaders for display purposes */
                        if (points == chosen_points &&
                            thread_group_leader(chosen))
                                continue;

                        if (chosen)
                                put_task_struct(chosen);
                        chosen = task;
                        chosen_points = points;
                        get_task_struct(chosen);
                }
                css_task_iter_end(&it);
        }

        if (!chosen)
                return;
        points = chosen_points * 1000 / totalpages;
        oom_kill_process(chosen, gfp_mask, order, points, totalpages, memcg,
                         NULL, "Memory cgroup out of memory");
}

#if MAX_NUMNODES > 1

/**
 * test_mem_cgroup_node_reclaimable
 * @memcg: the target memcg
 * @nid: the node ID to be checked.
 * @noswap : specify true here if the user wants flle only information.
 *
 * This function returns whether the specified memcg contains any
 * reclaimable pages on a node. Returns true if there are any reclaimable
 * pages in the node.
 */
static bool test_mem_cgroup_node_reclaimable(struct mem_cgroup *memcg,
                int nid, bool noswap)
{
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_FILE))
                return true;
        if (noswap || !total_swap_pages)
                return false;
        if (mem_cgroup_node_nr_lru_pages(memcg, nid, LRU_ALL_ANON))
                return true;
        return false;

}

/*
 * Always updating the nodemask is not very good - even if we have an empty
 * list or the wrong list here, we can start from some node and traverse all
 * nodes based on the zonelist. So update the list loosely once per 10 secs.
 *
 */
static void mem_cgroup_may_update_nodemask(struct mem_cgroup *memcg)
{
        int nid;
        /*
         * numainfo_events > 0 means there was at least NUMAINFO_EVENTS_TARGET
         * pagein/pageout changes since the last update.
         */
        if (!atomic_read(&memcg->numainfo_events))
                return;
        if (atomic_inc_return(&memcg->numainfo_updating) > 1)
                return;

        /* make a nodemask where this memcg uses memory from */
        memcg->scan_nodes = node_states[N_MEMORY];

        for_each_node_mask(nid, node_states[N_MEMORY]) {

                if (!test_mem_cgroup_node_reclaimable(memcg, nid, false))
                        node_clear(nid, memcg->scan_nodes);
        }

        atomic_set(&memcg->numainfo_events, 0);
        atomic_set(&memcg->numainfo_updating, 0);
}

/*
 * Selecting a node where we start reclaim from. Because what we need is just
 * reducing usage counter, start from anywhere is O,K. Considering
 * memory reclaim from current node, there are pros. and cons.
 *
 * Freeing memory from current node means freeing memory from a node which
 * we'll use or we've used. So, it may make LRU bad. And if several threads
 * hit limits, it will see a contention on a node. But freeing from remote
 * node means more costs for memory reclaim because of memory latency.
 *
 * Now, we use round-robin. Better algorithm is welcomed.
 */
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        int node;

        mem_cgroup_may_update_nodemask(memcg);
        node = memcg->last_scanned_node;

        node = next_node(node, memcg->scan_nodes);
        if (node == MAX_NUMNODES)
                node = first_node(memcg->scan_nodes);
        /*
         * We call this when we hit limit, not when pages are added to LRU.
         * No LRU may hold pages because all pages are UNEVICTABLE or
         * memcg is too small and all pages are not on LRU. In that case,
         * we use curret node.
         */
        if (unlikely(node == MAX_NUMNODES))
                node = numa_node_id();

        memcg->last_scanned_node = node;
        return node;
}
#else
int mem_cgroup_select_victim_node(struct mem_cgroup *memcg)
{
        return 0;
}
#endif

static int mem_cgroup_soft_reclaim(struct mem_cgroup *root_memcg,
                                   struct zone *zone,
                                   gfp_t gfp_mask,
                                   unsigned long *total_scanned)
{
        struct mem_cgroup *victim = NULL;
        int total = 0;
        int loop = 0;
        unsigned long excess;
        unsigned long nr_scanned;
        struct mem_cgroup_reclaim_cookie reclaim = {
                .zone = zone,
                .priority = 0,
        };

        excess = soft_limit_excess(root_memcg);

        while (1) {
                victim = mem_cgroup_iter(root_memcg, victim, &reclaim);
                if (!victim) {
                        loop++;
                        if (loop >= 2) {
                                /*
                                 * If we have not been able to reclaim
                                 * anything, it might because there are
                                 * no reclaimable pages under this hierarchy
                                 */
                                if (!total)
                                        break;
                                /*
                                 * We want to do more targeted reclaim.
                                 * excess >> 2 is not to excessive so as to
                                 * reclaim too much, nor too less that we keep
                                 * coming back to reclaim from this cgroup
                                 */
                                if (total >= (excess >> 2) ||
                                        (loop > MEM_CGROUP_MAX_RECLAIM_LOOPS))
                                        break;
                        }
                        continue;
                }
                total += mem_cgroup_shrink_node_zone(victim, gfp_mask, false,
                                                     zone, &nr_scanned);
                *total_scanned += nr_scanned;
                if (!soft_limit_excess(root_memcg))
                        break;
        }
        mem_cgroup_iter_break(root_memcg, victim);
        return total;
}

#ifdef CONFIG_LOCKDEP
static struct lockdep_map memcg_oom_lock_dep_map = {
        .name = "memcg_oom_lock",
};
#endif

static DEFINE_SPINLOCK(memcg_oom_lock);

/*
 * Check OOM-Killer is already running under our hierarchy.
 * If someone is running, return false.
 */
static bool mem_cgroup_oom_trylock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter, *failed = NULL;

        spin_lock(&memcg_oom_lock);

        for_each_mem_cgroup_tree(iter, memcg) {
                if (iter->oom_lock) {
                        /*
                         * this subtree of our hierarchy is already locked
                         * so we cannot give a lock.
                         */
                        failed = iter;
                        mem_cgroup_iter_break(memcg, iter);
                        break;
                } else
                        iter->oom_lock = true;
        }

        if (failed) {
                /*
                 * OK, we failed to lock the whole subtree so we have
                 * to clean up what we set up to the failing subtree
                 */
                for_each_mem_cgroup_tree(iter, memcg) {
                        if (iter == failed) {
                                mem_cgroup_iter_break(memcg, iter);
                                break;
                        }
                        iter->oom_lock = false;
                }
        } else
                mutex_acquire(&memcg_oom_lock_dep_map, 0, 1, _RET_IP_);

        spin_unlock(&memcg_oom_lock);

        return !failed;
}

static void mem_cgroup_oom_unlock(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        spin_lock(&memcg_oom_lock);
        mutex_release(&memcg_oom_lock_dep_map, 1, _RET_IP_);
        for_each_mem_cgroup_tree(iter, memcg)
                iter->oom_lock = false;
        spin_unlock(&memcg_oom_lock);
}

static void mem_cgroup_mark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                atomic_inc(&iter->under_oom);
}

static void mem_cgroup_unmark_under_oom(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        /*
         * When a new child is created while the hierarchy is under oom,
         * mem_cgroup_oom_lock() may not be called. We have to use
         * atomic_add_unless() here.
         */
        for_each_mem_cgroup_tree(iter, memcg)
                atomic_add_unless(&iter->under_oom, -1, 0);
}

static DECLARE_WAIT_QUEUE_HEAD(memcg_oom_waitq);

struct oom_wait_info {
        struct mem_cgroup *memcg;
        wait_queue_t    wait;
};

static int memcg_oom_wake_function(wait_queue_t *wait,
        unsigned mode, int sync, void *arg)
{
        struct mem_cgroup *wake_memcg = (struct mem_cgroup *)arg;
        struct mem_cgroup *oom_wait_memcg;
        struct oom_wait_info *oom_wait_info;

        oom_wait_info = container_of(wait, struct oom_wait_info, wait);
        oom_wait_memcg = oom_wait_info->memcg;

        if (!mem_cgroup_is_descendant(wake_memcg, oom_wait_memcg) &&
            !mem_cgroup_is_descendant(oom_wait_memcg, wake_memcg))
                return 0;
        return autoremove_wake_function(wait, mode, sync, arg);
}

static void memcg_wakeup_oom(struct mem_cgroup *memcg)
{
        atomic_inc(&memcg->oom_wakeups);
        /* for filtering, pass "memcg" as argument. */
        __wake_up(&memcg_oom_waitq, TASK_NORMAL, 0, memcg);
}

static void memcg_oom_recover(struct mem_cgroup *memcg)
{
        if (memcg && atomic_read(&memcg->under_oom))
                memcg_wakeup_oom(memcg);
}

static void mem_cgroup_oom(struct mem_cgroup *memcg, gfp_t mask, int order)
{
        if (!current->memcg_oom.may_oom)
                return;
        /*
         * We are in the middle of the charge context here, so we
         * don't want to block when potentially sitting on a callstack
         * that holds all kinds of filesystem and mm locks.
         *
         * Also, the caller may handle a failed allocation gracefully
         * (like optional page cache readahead) and so an OOM killer
         * invocation might not even be necessary.
         *
         * That's why we don't do anything here except remember the
         * OOM context and then deal with it at the end of the page
         * fault when the stack is unwound, the locks are released,
         * and when we know whether the fault was overall successful.
         */
        css_get(&memcg->css);
        current->memcg_oom.memcg = memcg;
        current->memcg_oom.gfp_mask = mask;
        current->memcg_oom.order = order;
}

/**
 * mem_cgroup_oom_synchronize - complete memcg OOM handling
 * @handle: actually kill/wait or just clean up the OOM state
 *
 * This has to be called at the end of a page fault if the memcg OOM
 * handler was enabled.
 *
 * Memcg supports userspace OOM handling where failed allocations must
 * sleep on a waitqueue until the userspace task resolves the
 * situation.  Sleeping directly in the charge context with all kinds
 * of locks held is not a good idea, instead we remember an OOM state
 * in the task and mem_cgroup_oom_synchronize() has to be called at
 * the end of the page fault to complete the OOM handling.
 *
 * Returns %true if an ongoing memcg OOM situation was detected and
 * completed, %false otherwise.
 */
bool mem_cgroup_oom_synchronize(bool handle)
{
        struct mem_cgroup *memcg = current->memcg_oom.memcg;
        struct oom_wait_info owait;
        bool locked;

        /* OOM is global, do not handle */
        if (!memcg)
                return false;

        if (!handle || oom_killer_disabled)
                goto cleanup;

        owait.memcg = memcg;
        owait.wait.flags = 0;
        owait.wait.func = memcg_oom_wake_function;
        owait.wait.private = current;
        INIT_LIST_HEAD(&owait.wait.task_list);

        prepare_to_wait(&memcg_oom_waitq, &owait.wait, TASK_KILLABLE);
        mem_cgroup_mark_under_oom(memcg);

        locked = mem_cgroup_oom_trylock(memcg);

        if (locked)
                mem_cgroup_oom_notify(memcg);

        if (locked && !memcg->oom_kill_disable) {
                mem_cgroup_unmark_under_oom(memcg);
                finish_wait(&memcg_oom_waitq, &owait.wait);
                mem_cgroup_out_of_memory(memcg, current->memcg_oom.gfp_mask,
                                         current->memcg_oom.order);
        } else {
                schedule();
                mem_cgroup_unmark_under_oom(memcg);
                finish_wait(&memcg_oom_waitq, &owait.wait);
        }

        if (locked) {
                mem_cgroup_oom_unlock(memcg);
                /*
                 * There is no guarantee that an OOM-lock contender
                 * sees the wakeups triggered by the OOM kill
                 * uncharges.  Wake any sleepers explicitely.
                 */
                memcg_oom_recover(memcg);
        }
cleanup:
        current->memcg_oom.memcg = NULL;
        css_put(&memcg->css);
        return true;
}

/**
 * mem_cgroup_begin_page_stat - begin a page state statistics transaction
 * @page: page that is going to change accounted state
 *
 * This function must mark the beginning of an accounted page state
 * change to prevent double accounting when the page is concurrently
 * being moved to another memcg:
 *
 *   memcg = mem_cgroup_begin_page_stat(page);
 *   if (TestClearPageState(page))
 *     mem_cgroup_update_page_stat(memcg, state, -1);
 *   mem_cgroup_end_page_stat(memcg);
 */
struct mem_cgroup *mem_cgroup_begin_page_stat(struct page *page)
{
        struct mem_cgroup *memcg;
        unsigned long flags;

        /*
         * The RCU lock is held throughout the transaction.  The fast
         * path can get away without acquiring the memcg->move_lock
         * because page moving starts with an RCU grace period.
         *
         * The RCU lock also protects the memcg from being freed when
         * the page state that is going to change is the only thing
         * preventing the page from being uncharged.
         * E.g. end-writeback clearing PageWriteback(), which allows
         * migration to go ahead and uncharge the page before the
         * account transaction might be complete.
         */
        rcu_read_lock();

        if (mem_cgroup_disabled())
                return NULL;
again:
        memcg = page->mem_cgroup;
        if (unlikely(!memcg))
                return NULL;

        if (atomic_read(&memcg->moving_account) <= 0)
                return memcg;

        spin_lock_irqsave(&memcg->move_lock, flags);
        if (memcg != page->mem_cgroup) {
                spin_unlock_irqrestore(&memcg->move_lock, flags);
                goto again;
        }

        /*
         * When charge migration first begins, we can have locked and
         * unlocked page stat updates happening concurrently.  Track
         * the task who has the lock for mem_cgroup_end_page_stat().
         */
        memcg->move_lock_task = current;
        memcg->move_lock_flags = flags;

        return memcg;
}

/**
 * mem_cgroup_end_page_stat - finish a page state statistics transaction
 * @memcg: the memcg that was accounted against
 */
void mem_cgroup_end_page_stat(struct mem_cgroup *memcg)
{
        if (memcg && memcg->move_lock_task == current) {
                unsigned long flags = memcg->move_lock_flags;

                memcg->move_lock_task = NULL;
                memcg->move_lock_flags = 0;

                spin_unlock_irqrestore(&memcg->move_lock, flags);
        }

        rcu_read_unlock();
}

/**
 * mem_cgroup_update_page_stat - update page state statistics
 * @memcg: memcg to account against
 * @idx: page state item to account
 * @val: number of pages (positive or negative)
 *
 * See mem_cgroup_begin_page_stat() for locking requirements.
 */
void mem_cgroup_update_page_stat(struct mem_cgroup *memcg,
                                 enum mem_cgroup_stat_index idx, int val)
{
        VM_BUG_ON(!rcu_read_lock_held());

        if (memcg)
                this_cpu_add(memcg->stat->count[idx], val);
}

/*
 * size of first charge trial. "32" comes from vmscan.c's magic value.
 * TODO: maybe necessary to use big numbers in big irons.
 */
#define CHARGE_BATCH    32U
struct memcg_stock_pcp {
        struct mem_cgroup *cached; /* this never be root cgroup */
        unsigned int nr_pages;
        struct work_struct work;
        unsigned long flags;
#define FLUSHING_CACHED_CHARGE  0
};
static DEFINE_PER_CPU(struct memcg_stock_pcp, memcg_stock);
static DEFINE_MUTEX(percpu_charge_mutex);

/**
 * consume_stock: Try to consume stocked charge on this cpu.
 * @memcg: memcg to consume from.
 * @nr_pages: how many pages to charge.
 *
 * The charges will only happen if @memcg matches the current cpu's memcg
 * stock, and at least @nr_pages are available in that stock.  Failure to
 * service an allocation will refill the stock.
 *
 * returns true if successful, false otherwise.
 */
static bool consume_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        struct memcg_stock_pcp *stock;
        bool ret = false;

        if (nr_pages > CHARGE_BATCH)
                return ret;

        stock = &get_cpu_var(memcg_stock);
        if (memcg == stock->cached && stock->nr_pages >= nr_pages) {
                stock->nr_pages -= nr_pages;
                ret = true;
        }
        put_cpu_var(memcg_stock);
        return ret;
}

/*
 * Returns stocks cached in percpu and reset cached information.
 */
static void drain_stock(struct memcg_stock_pcp *stock)
{
        struct mem_cgroup *old = stock->cached;

        if (stock->nr_pages) {
                page_counter_uncharge(&old->memory, stock->nr_pages);
                if (do_swap_account)
                        page_counter_uncharge(&old->memsw, stock->nr_pages);
                css_put_many(&old->css, stock->nr_pages);
                stock->nr_pages = 0;
        }
        stock->cached = NULL;
}

/*
 * This must be called under preempt disabled or must be called by
 * a thread which is pinned to local cpu.
 */
static void drain_local_stock(struct work_struct *dummy)
{
        struct memcg_stock_pcp *stock = this_cpu_ptr(&memcg_stock);
        drain_stock(stock);
        clear_bit(FLUSHING_CACHED_CHARGE, &stock->flags);
}

static void __init memcg_stock_init(void)
{
        int cpu;

        for_each_possible_cpu(cpu) {
                struct memcg_stock_pcp *stock =
                                        &per_cpu(memcg_stock, cpu);
                INIT_WORK(&stock->work, drain_local_stock);
        }
}

/*
 * Cache charges(val) to local per_cpu area.
 * This will be consumed by consume_stock() function, later.
 */
static void refill_stock(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        struct memcg_stock_pcp *stock = &get_cpu_var(memcg_stock);

        if (stock->cached != memcg) { /* reset if necessary */
                drain_stock(stock);
                stock->cached = memcg;
        }
        stock->nr_pages += nr_pages;
        put_cpu_var(memcg_stock);
}

/*
 * Drains all per-CPU charge caches for given root_memcg resp. subtree
 * of the hierarchy under it.
 */
static void drain_all_stock(struct mem_cgroup *root_memcg)
{
        int cpu, curcpu;

        /* If someone's already draining, avoid adding running more workers. */
        if (!mutex_trylock(&percpu_charge_mutex))
                return;
        /* Notify other cpus that system-wide "drain" is running */
        get_online_cpus();
        curcpu = get_cpu();
        for_each_online_cpu(cpu) {
                struct memcg_stock_pcp *stock = &per_cpu(memcg_stock, cpu);
                struct mem_cgroup *memcg;

                memcg = stock->cached;
                if (!memcg || !stock->nr_pages)
                        continue;
                if (!mem_cgroup_is_descendant(memcg, root_memcg))
                        continue;
                if (!test_and_set_bit(FLUSHING_CACHED_CHARGE, &stock->flags)) {
                        if (cpu == curcpu)
                                drain_local_stock(&stock->work);
                        else
                                schedule_work_on(cpu, &stock->work);
                }
        }
        put_cpu();
        put_online_cpus();
        mutex_unlock(&percpu_charge_mutex);
}

/*
 * This function drains percpu counter value from DEAD cpu and
 * move it to local cpu. Note that this function can be preempted.
 */
static void mem_cgroup_drain_pcp_counter(struct mem_cgroup *memcg, int cpu)
{
        int i;

        spin_lock(&memcg->pcp_counter_lock);
        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                long x = per_cpu(memcg->stat->count[i], cpu);

                per_cpu(memcg->stat->count[i], cpu) = 0;
                memcg->nocpu_base.count[i] += x;
        }
        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
                unsigned long x = per_cpu(memcg->stat->events[i], cpu);

                per_cpu(memcg->stat->events[i], cpu) = 0;
                memcg->nocpu_base.events[i] += x;
        }
        spin_unlock(&memcg->pcp_counter_lock);
}

static int memcg_cpu_hotplug_callback(struct notifier_block *nb,
                                        unsigned long action,
                                        void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        struct memcg_stock_pcp *stock;
        struct mem_cgroup *iter;

        if (action == CPU_ONLINE)
                return NOTIFY_OK;

        if (action != CPU_DEAD && action != CPU_DEAD_FROZEN)
                return NOTIFY_OK;

        for_each_mem_cgroup(iter)
                mem_cgroup_drain_pcp_counter(iter, cpu);

        stock = &per_cpu(memcg_stock, cpu);
        drain_stock(stock);
        return NOTIFY_OK;
}

static int try_charge(struct mem_cgroup *memcg, gfp_t gfp_mask,
                      unsigned int nr_pages)
{
        unsigned int batch = max(CHARGE_BATCH, nr_pages);
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;
        struct mem_cgroup *mem_over_limit;
        struct page_counter *counter;
        unsigned long nr_reclaimed;
        bool may_swap = true;
        bool drained = false;
        int ret = 0;

        if (mem_cgroup_is_root(memcg))
                goto done;
retry:
        if (consume_stock(memcg, nr_pages))
                goto done;

        if (!do_swap_account ||
            !page_counter_try_charge(&memcg->memsw, batch, &counter)) {
                if (!page_counter_try_charge(&memcg->memory, batch, &counter))
                        goto done_restock;
                if (do_swap_account)
                        page_counter_uncharge(&memcg->memsw, batch);
                mem_over_limit = mem_cgroup_from_counter(counter, memory);
        } else {
                mem_over_limit = mem_cgroup_from_counter(counter, memsw);
                may_swap = false;
        }

        if (batch > nr_pages) {
                batch = nr_pages;
                goto retry;
        }

        /*
         * Unlike in global OOM situations, memcg is not in a physical
         * memory shortage.  Allow dying and OOM-killed tasks to
         * bypass the last charges so that they can exit quickly and
         * free their memory.
         */
        if (unlikely(test_thread_flag(TIF_MEMDIE) ||
                     fatal_signal_pending(current) ||
                     current->flags & PF_EXITING))
                goto bypass;

        if (unlikely(task_in_memcg_oom(current)))
                goto nomem;

        if (!(gfp_mask & __GFP_WAIT))
                goto nomem;

        mem_cgroup_events(mem_over_limit, MEMCG_MAX, 1);

        nr_reclaimed = try_to_free_mem_cgroup_pages(mem_over_limit, nr_pages,
                                                    gfp_mask, may_swap);

        if (mem_cgroup_margin(mem_over_limit) >= nr_pages)
                goto retry;

        if (!drained) {
                drain_all_stock(mem_over_limit);
                drained = true;
                goto retry;
        }

        if (gfp_mask & __GFP_NORETRY)
                goto nomem;
        /*
         * Even though the limit is exceeded at this point, reclaim
         * may have been able to free some pages.  Retry the charge
         * before killing the task.
         *
         * Only for regular pages, though: huge pages are rather
         * unlikely to succeed so close to the limit, and we fall back
         * to regular pages anyway in case of failure.
         */
        if (nr_reclaimed && nr_pages <= (1 << PAGE_ALLOC_COSTLY_ORDER))
                goto retry;
        /*
         * At task move, charge accounts can be doubly counted. So, it's
         * better to wait until the end of task_move if something is going on.
         */
        if (mem_cgroup_wait_acct_move(mem_over_limit))
                goto retry;

        if (nr_retries--)
                goto retry;

        if (gfp_mask & __GFP_NOFAIL)
                goto bypass;

        if (fatal_signal_pending(current))
                goto bypass;

        mem_cgroup_events(mem_over_limit, MEMCG_OOM, 1);

        mem_cgroup_oom(mem_over_limit, gfp_mask, get_order(nr_pages));
nomem:
        if (!(gfp_mask & __GFP_NOFAIL))
                return -ENOMEM;
bypass:
        return -EINTR;

done_restock:
        css_get_many(&memcg->css, batch);
        if (batch > nr_pages)
                refill_stock(memcg, batch - nr_pages);
        /*
         * If the hierarchy is above the normal consumption range,
         * make the charging task trim their excess contribution.
         */
        do {
                if (page_counter_read(&memcg->memory) <= memcg->high)
                        continue;
                mem_cgroup_events(memcg, MEMCG_HIGH, 1);
                try_to_free_mem_cgroup_pages(memcg, nr_pages, gfp_mask, true);
        } while ((memcg = parent_mem_cgroup(memcg)));
done:
        return ret;
}

static void cancel_charge(struct mem_cgroup *memcg, unsigned int nr_pages)
{
        if (mem_cgroup_is_root(memcg))
                return;

        page_counter_uncharge(&memcg->memory, nr_pages);
        if (do_swap_account)
                page_counter_uncharge(&memcg->memsw, nr_pages);

        css_put_many(&memcg->css, nr_pages);
}

/*
 * A helper function to get mem_cgroup from ID. must be called under
 * rcu_read_lock().  The caller is responsible for calling
 * css_tryget_online() if the mem_cgroup is used for charging. (dropping
 * refcnt from swap can be called against removed memcg.)
 */
static struct mem_cgroup *mem_cgroup_lookup(unsigned short id)
{
        /* ID 0 is unused ID */
        if (!id)
                return NULL;
        return mem_cgroup_from_id(id);
}

/*
 * try_get_mem_cgroup_from_page - look up page's memcg association
 * @page: the page
 *
 * Look up, get a css reference, and return the memcg that owns @page.
 *
 * The page must be locked to prevent racing with swap-in and page
 * cache charges.  If coming from an unlocked page table, the caller
 * must ensure the page is on the LRU or this can race with charging.
 */
struct mem_cgroup *try_get_mem_cgroup_from_page(struct page *page)
{
        struct mem_cgroup *memcg;
        unsigned short id;
        swp_entry_t ent;

        VM_BUG_ON_PAGE(!PageLocked(page), page);

        memcg = page->mem_cgroup;
        if (memcg) {
                if (!css_tryget_online(&memcg->css))
                        memcg = NULL;
        } else if (PageSwapCache(page)) {
                ent.val = page_private(page);
                id = lookup_swap_cgroup_id(ent);
                rcu_read_lock();
                memcg = mem_cgroup_lookup(id);
                if (memcg && !css_tryget_online(&memcg->css))
                        memcg = NULL;
                rcu_read_unlock();
        }
        return memcg;
}

static void lock_page_lru(struct page *page, int *isolated)
{
        struct zone *zone = page_zone(page);

        spin_lock_irq(&zone->lru_lock);
        if (PageLRU(page)) {
                struct lruvec *lruvec;

                lruvec = mem_cgroup_page_lruvec(page, zone);
                ClearPageLRU(page);
                del_page_from_lru_list(page, lruvec, page_lru(page));
                *isolated = 1;
        } else
                *isolated = 0;
}

static void unlock_page_lru(struct page *page, int isolated)
{
        struct zone *zone = page_zone(page);

        if (isolated) {
                struct lruvec *lruvec;

                lruvec = mem_cgroup_page_lruvec(page, zone);
                VM_BUG_ON_PAGE(PageLRU(page), page);
                SetPageLRU(page);
                add_page_to_lru_list(page, lruvec, page_lru(page));
        }
        spin_unlock_irq(&zone->lru_lock);
}

static void commit_charge(struct page *page, struct mem_cgroup *memcg,
                          bool lrucare)
{
        int isolated;

        VM_BUG_ON_PAGE(page->mem_cgroup, page);

        /*
         * In some cases, SwapCache and FUSE(splice_buf->radixtree), the page
         * may already be on some other mem_cgroup's LRU.  Take care of it.
         */
        if (lrucare)
                lock_page_lru(page, &isolated);

        /*
         * Nobody should be changing or seriously looking at
         * page->mem_cgroup at this point:
         *
         * - the page is uncharged
         *
         * - the page is off-LRU
         *
         * - an anonymous fault has exclusive page access, except for
         *   a locked page table
         *
         * - a page cache insertion, a swapin fault, or a migration
         *   have the page locked
         */
        page->mem_cgroup = memcg;

        if (lrucare)
                unlock_page_lru(page, isolated);
}

#ifdef CONFIG_MEMCG_KMEM
int memcg_charge_kmem(struct mem_cgroup *memcg, gfp_t gfp,
                      unsigned long nr_pages)
{
        struct page_counter *counter;
        int ret = 0;

        ret = page_counter_try_charge(&memcg->kmem, nr_pages, &counter);
        if (ret < 0)
                return ret;

        ret = try_charge(memcg, gfp, nr_pages);
        if (ret == -EINTR)  {
                /*
                 * try_charge() chose to bypass to root due to OOM kill or
                 * fatal signal.  Since our only options are to either fail
                 * the allocation or charge it to this cgroup, do it as a
                 * temporary condition. But we can't fail. From a kmem/slab
                 * perspective, the cache has already been selected, by
                 * mem_cgroup_kmem_get_cache(), so it is too late to change
                 * our minds.
                 *
                 * This condition will only trigger if the task entered
                 * memcg_charge_kmem in a sane state, but was OOM-killed
                 * during try_charge() above. Tasks that were already dying
                 * when the allocation triggers should have been already
                 * directed to the root cgroup in memcontrol.h
                 */
                page_counter_charge(&memcg->memory, nr_pages);
                if (do_swap_account)
                        page_counter_charge(&memcg->memsw, nr_pages);
                css_get_many(&memcg->css, nr_pages);
                ret = 0;
        } else if (ret)
                page_counter_uncharge(&memcg->kmem, nr_pages);

        return ret;
}

void memcg_uncharge_kmem(struct mem_cgroup *memcg, unsigned long nr_pages)
{
        page_counter_uncharge(&memcg->memory, nr_pages);
        if (do_swap_account)
                page_counter_uncharge(&memcg->memsw, nr_pages);

        page_counter_uncharge(&memcg->kmem, nr_pages);

        css_put_many(&memcg->css, nr_pages);
}

/*
 * helper for acessing a memcg's index. It will be used as an index in the
 * child cache array in kmem_cache, and also to derive its name. This function
 * will return -1 when this is not a kmem-limited memcg.
 */
int memcg_cache_id(struct mem_cgroup *memcg)
{
        return memcg ? memcg->kmemcg_id : -1;
}

static int memcg_alloc_cache_id(void)
{
        int id, size;
        int err;

        id = ida_simple_get(&kmem_limited_groups,
                            0, MEMCG_CACHES_MAX_SIZE, GFP_KERNEL);
        if (id < 0)
                return id;

        if (id < memcg_limited_groups_array_size)
                return id;

        /*
         * There's no space for the new id in memcg_caches arrays,
         * so we have to grow them.
         */

        size = 2 * (id + 1);
        if (size < MEMCG_CACHES_MIN_SIZE)
                size = MEMCG_CACHES_MIN_SIZE;
        else if (size > MEMCG_CACHES_MAX_SIZE)
                size = MEMCG_CACHES_MAX_SIZE;

        err = memcg_update_all_caches(size);
        if (err) {
                ida_simple_remove(&kmem_limited_groups, id);
                return err;
        }
        return id;
}

static void memcg_free_cache_id(int id)
{
        ida_simple_remove(&kmem_limited_groups, id);
}

/*
 * We should update the current array size iff all caches updates succeed. This
 * can only be done from the slab side. The slab mutex needs to be held when
 * calling this.
 */
void memcg_update_array_size(int num)
{
        memcg_limited_groups_array_size = num;
}

struct memcg_kmem_cache_create_work {
        struct mem_cgroup *memcg;
        struct kmem_cache *cachep;
        struct work_struct work;
};

static void memcg_kmem_cache_create_func(struct work_struct *w)
{
        struct memcg_kmem_cache_create_work *cw =
                container_of(w, struct memcg_kmem_cache_create_work, work);
        struct mem_cgroup *memcg = cw->memcg;
        struct kmem_cache *cachep = cw->cachep;

        memcg_create_kmem_cache(memcg, cachep);

        css_put(&memcg->css);
        kfree(cw);
}

/*
 * Enqueue the creation of a per-memcg kmem_cache.
 */
static void __memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
                                               struct kmem_cache *cachep)
{
        struct memcg_kmem_cache_create_work *cw;

        cw = kmalloc(sizeof(*cw), GFP_NOWAIT);
        if (!cw)
                return;

        css_get(&memcg->css);

        cw->memcg = memcg;
        cw->cachep = cachep;
        INIT_WORK(&cw->work, memcg_kmem_cache_create_func);

        schedule_work(&cw->work);
}

static void memcg_schedule_kmem_cache_create(struct mem_cgroup *memcg,
                                             struct kmem_cache *cachep)
{
        /*
         * We need to stop accounting when we kmalloc, because if the
         * corresponding kmalloc cache is not yet created, the first allocation
         * in __memcg_schedule_kmem_cache_create will recurse.
         *
         * However, it is better to enclose the whole function. Depending on
         * the debugging options enabled, INIT_WORK(), for instance, can
         * trigger an allocation. This too, will make us recurse. Because at
         * this point we can't allow ourselves back into memcg_kmem_get_cache,
         * the safest choice is to do it like this, wrapping the whole function.
         */
        current->memcg_kmem_skip_account = 1;
        __memcg_schedule_kmem_cache_create(memcg, cachep);
        current->memcg_kmem_skip_account = 0;
}

/*
 * Return the kmem_cache we're supposed to use for a slab allocation.
 * We try to use the current memcg's version of the cache.
 *
 * If the cache does not exist yet, if we are the first user of it,
 * we either create it immediately, if possible, or create it asynchronously
 * in a workqueue.
 * In the latter case, we will let the current allocation go through with
 * the original cache.
 *
 * Can't be called in interrupt context or from kernel threads.
 * This function needs to be called with rcu_read_lock() held.
 */
struct kmem_cache *__memcg_kmem_get_cache(struct kmem_cache *cachep)
{
        struct mem_cgroup *memcg;
        struct kmem_cache *memcg_cachep;

        VM_BUG_ON(!cachep->memcg_params);
        VM_BUG_ON(!cachep->memcg_params->is_root_cache);

        if (current->memcg_kmem_skip_account)
                return cachep;

        memcg = get_mem_cgroup_from_mm(current->mm);
        if (!memcg_kmem_is_active(memcg))
                goto out;

        memcg_cachep = cache_from_memcg_idx(cachep, memcg_cache_id(memcg));
        if (likely(memcg_cachep))
                return memcg_cachep;

        /*
         * If we are in a safe context (can wait, and not in interrupt
         * context), we could be be predictable and return right away.
         * This would guarantee that the allocation being performed
         * already belongs in the new cache.
         *
         * However, there are some clashes that can arrive from locking.
         * For instance, because we acquire the slab_mutex while doing
         * memcg_create_kmem_cache, this means no further allocation
         * could happen with the slab_mutex held. So it's better to
         * defer everything.
         */
        memcg_schedule_kmem_cache_create(memcg, cachep);
out:
        css_put(&memcg->css);
        return cachep;
}

void __memcg_kmem_put_cache(struct kmem_cache *cachep)
{
        if (!is_root_cache(cachep))
                css_put(&cachep->memcg_params->memcg->css);
}

/*
 * We need to verify if the allocation against current->mm->owner's memcg is
 * possible for the given order. But the page is not allocated yet, so we'll
 * need a further commit step to do the final arrangements.
 *
 * It is possible for the task to switch cgroups in this mean time, so at
 * commit time, we can't rely on task conversion any longer.  We'll then use
 * the handle argument to return to the caller which cgroup we should commit
 * against. We could also return the memcg directly and avoid the pointer
 * passing, but a boolean return value gives better semantics considering
 * the compiled-out case as well.
 *
 * Returning true means the allocation is possible.
 */
bool
__memcg_kmem_newpage_charge(gfp_t gfp, struct mem_cgroup **_memcg, int order)
{
        struct mem_cgroup *memcg;
        int ret;

        *_memcg = NULL;

        memcg = get_mem_cgroup_from_mm(current->mm);

        if (!memcg_kmem_is_active(memcg)) {
                css_put(&memcg->css);
                return true;
        }

        ret = memcg_charge_kmem(memcg, gfp, 1 << order);
        if (!ret)
                *_memcg = memcg;

        css_put(&memcg->css);
        return (ret == 0);
}

void __memcg_kmem_commit_charge(struct page *page, struct mem_cgroup *memcg,
                              int order)
{
        VM_BUG_ON(mem_cgroup_is_root(memcg));

        /* The page allocation failed. Revert */
        if (!page) {
                memcg_uncharge_kmem(memcg, 1 << order);
                return;
        }
        page->mem_cgroup = memcg;
}

void __memcg_kmem_uncharge_pages(struct page *page, int order)
{
        struct mem_cgroup *memcg = page->mem_cgroup;

        if (!memcg)
                return;

        VM_BUG_ON_PAGE(mem_cgroup_is_root(memcg), page);

        memcg_uncharge_kmem(memcg, 1 << order);
        page->mem_cgroup = NULL;
}
#endif /* CONFIG_MEMCG_KMEM */

#ifdef CONFIG_TRANSPARENT_HUGEPAGE

/*
 * Because tail pages are not marked as "used", set it. We're under
 * zone->lru_lock, 'splitting on pmd' and compound_lock.
 * charge/uncharge will be never happen and move_account() is done under
 * compound_lock(), so we don't have to take care of races.
 */
void mem_cgroup_split_huge_fixup(struct page *head)
{
        int i;

        if (mem_cgroup_disabled())
                return;

        for (i = 1; i < HPAGE_PMD_NR; i++)
                head[i].mem_cgroup = head->mem_cgroup;

        __this_cpu_sub(head->mem_cgroup->stat->count[MEM_CGROUP_STAT_RSS_HUGE],
                       HPAGE_PMD_NR);
}
#endif /* CONFIG_TRANSPARENT_HUGEPAGE */

/**
 * mem_cgroup_move_account - move account of the page
 * @page: the page
 * @nr_pages: number of regular pages (>1 for huge pages)
 * @from: mem_cgroup which the page is moved from.
 * @to: mem_cgroup which the page is moved to. @from != @to.
 *
 * The caller must confirm following.
 * - page is not on LRU (isolate_page() is useful.)
 * - compound_lock is held when nr_pages > 1
 *
 * This function doesn't do "charge" to new cgroup and doesn't do "uncharge"
 * from old cgroup.
 */
static int mem_cgroup_move_account(struct page *page,
                                   unsigned int nr_pages,
                                   struct mem_cgroup *from,
                                   struct mem_cgroup *to)
{
        unsigned long flags;
        int ret;

        VM_BUG_ON(from == to);
        VM_BUG_ON_PAGE(PageLRU(page), page);
        /*
         * The page is isolated from LRU. So, collapse function
         * will not handle this page. But page splitting can happen.
         * Do this check under compound_page_lock(). The caller should
         * hold it.
         */
        ret = -EBUSY;
        if (nr_pages > 1 && !PageTransHuge(page))
                goto out;

        /*
         * Prevent mem_cgroup_migrate() from looking at page->mem_cgroup
         * of its source page while we change it: page migration takes
         * both pages off the LRU, but page cache replacement doesn't.
         */
        if (!trylock_page(page))
                goto out;

        ret = -EINVAL;
        if (page->mem_cgroup != from)
                goto out_unlock;

        spin_lock_irqsave(&from->move_lock, flags);

        if (!PageAnon(page) && page_mapped(page)) {
                __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
                               nr_pages);
                __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_FILE_MAPPED],
                               nr_pages);
        }

        if (PageWriteback(page)) {
                __this_cpu_sub(from->stat->count[MEM_CGROUP_STAT_WRITEBACK],
                               nr_pages);
                __this_cpu_add(to->stat->count[MEM_CGROUP_STAT_WRITEBACK],
                               nr_pages);
        }

        /*
         * It is safe to change page->mem_cgroup here because the page
         * is referenced, charged, and isolated - we can't race with
         * uncharging, charging, migration, or LRU putback.
         */

        /* caller should have done css_get */
        page->mem_cgroup = to;
        spin_unlock_irqrestore(&from->move_lock, flags);

        ret = 0;

        local_irq_disable();
        mem_cgroup_charge_statistics(to, page, nr_pages);
        memcg_check_events(to, page);
        mem_cgroup_charge_statistics(from, page, -nr_pages);
        memcg_check_events(from, page);
        local_irq_enable();
out_unlock:
        unlock_page(page);
out:
        return ret;
}

#ifdef CONFIG_MEMCG_SWAP
static void mem_cgroup_swap_statistics(struct mem_cgroup *memcg,
                                         bool charge)
{
        int val = (charge) ? 1 : -1;
        this_cpu_add(memcg->stat->count[MEM_CGROUP_STAT_SWAP], val);
}

/**
 * mem_cgroup_move_swap_account - move swap charge and swap_cgroup's record.
 * @entry: swap entry to be moved
 * @from:  mem_cgroup which the entry is moved from
 * @to:  mem_cgroup which the entry is moved to
 *
 * It succeeds only when the swap_cgroup's record for this entry is the same
 * as the mem_cgroup's id of @from.
 *
 * Returns 0 on success, -EINVAL on failure.
 *
 * The caller must have charged to @to, IOW, called page_counter_charge() about
 * both res and memsw, and called css_get().
 */
static int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        unsigned short old_id, new_id;

        old_id = mem_cgroup_id(from);
        new_id = mem_cgroup_id(to);

        if (swap_cgroup_cmpxchg(entry, old_id, new_id) == old_id) {
                mem_cgroup_swap_statistics(from, false);
                mem_cgroup_swap_statistics(to, true);
                return 0;
        }
        return -EINVAL;
}
#else
static inline int mem_cgroup_move_swap_account(swp_entry_t entry,
                                struct mem_cgroup *from, struct mem_cgroup *to)
{
        return -EINVAL;
}
#endif

static DEFINE_MUTEX(memcg_limit_mutex);

static int mem_cgroup_resize_limit(struct mem_cgroup *memcg,
                                   unsigned long limit)
{
        unsigned long curusage;
        unsigned long oldusage;
        bool enlarge = false;
        int retry_count;
        int ret;

        /*
         * For keeping hierarchical_reclaim simple, how long we should retry
         * is depends on callers. We set our retry-count to be function
         * of # of children which we should visit in this loop.
         */
        retry_count = MEM_CGROUP_RECLAIM_RETRIES *
                      mem_cgroup_count_children(memcg);

        oldusage = page_counter_read(&memcg->memory);

        do {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }

                mutex_lock(&memcg_limit_mutex);
                if (limit > memcg->memsw.limit) {
                        mutex_unlock(&memcg_limit_mutex);
                        ret = -EINVAL;
                        break;
                }
                if (limit > memcg->memory.limit)
                        enlarge = true;
                ret = page_counter_limit(&memcg->memory, limit);
                mutex_unlock(&memcg_limit_mutex);

                if (!ret)
                        break;

                try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, true);

                curusage = page_counter_read(&memcg->memory);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        } while (retry_count);

        if (!ret && enlarge)
                memcg_oom_recover(memcg);

        return ret;
}

static int mem_cgroup_resize_memsw_limit(struct mem_cgroup *memcg,
                                         unsigned long limit)
{
        unsigned long curusage;
        unsigned long oldusage;
        bool enlarge = false;
        int retry_count;
        int ret;

        /* see mem_cgroup_resize_res_limit */
        retry_count = MEM_CGROUP_RECLAIM_RETRIES *
                      mem_cgroup_count_children(memcg);

        oldusage = page_counter_read(&memcg->memsw);

        do {
                if (signal_pending(current)) {
                        ret = -EINTR;
                        break;
                }

                mutex_lock(&memcg_limit_mutex);
                if (limit < memcg->memory.limit) {
                        mutex_unlock(&memcg_limit_mutex);
                        ret = -EINVAL;
                        break;
                }
                if (limit > memcg->memsw.limit)
                        enlarge = true;
                ret = page_counter_limit(&memcg->memsw, limit);
                mutex_unlock(&memcg_limit_mutex);

                if (!ret)
                        break;

                try_to_free_mem_cgroup_pages(memcg, 1, GFP_KERNEL, false);

                curusage = page_counter_read(&memcg->memsw);
                /* Usage is reduced ? */
                if (curusage >= oldusage)
                        retry_count--;
                else
                        oldusage = curusage;
        } while (retry_count);

        if (!ret && enlarge)
                memcg_oom_recover(memcg);

        return ret;
}

unsigned long mem_cgroup_soft_limit_reclaim(struct zone *zone, int order,
                                            gfp_t gfp_mask,
                                            unsigned long *total_scanned)
{
        unsigned long nr_reclaimed = 0;
        struct mem_cgroup_per_zone *mz, *next_mz = NULL;
        unsigned long reclaimed;
        int loop = 0;
        struct mem_cgroup_tree_per_zone *mctz;
        unsigned long excess;
        unsigned long nr_scanned;

        if (order > 0)
                return 0;

        mctz = soft_limit_tree_node_zone(zone_to_nid(zone), zone_idx(zone));
        /*
         * This loop can run a while, specially if mem_cgroup's continuously
         * keep exceeding their soft limit and putting the system under
         * pressure
         */
        do {
                if (next_mz)
                        mz = next_mz;
                else
                        mz = mem_cgroup_largest_soft_limit_node(mctz);
                if (!mz)
                        break;

                nr_scanned = 0;
                reclaimed = mem_cgroup_soft_reclaim(mz->memcg, zone,
                                                    gfp_mask, &nr_scanned);
                nr_reclaimed += reclaimed;
                *total_scanned += nr_scanned;
                spin_lock_irq(&mctz->lock);
                __mem_cgroup_remove_exceeded(mz, mctz);

                /*
                 * If we failed to reclaim anything from this memory cgroup
                 * it is time to move on to the next cgroup
                 */
                next_mz = NULL;
                if (!reclaimed)
                        next_mz = __mem_cgroup_largest_soft_limit_node(mctz);

                excess = soft_limit_excess(mz->memcg);
                /*
                 * One school of thought says that we should not add
                 * back the node to the tree if reclaim returns 0.
                 * But our reclaim could return 0, simply because due
                 * to priority we are exposing a smaller subset of
                 * memory to reclaim from. Consider this as a longer
                 * term TODO.
                 */
                /* If excess == 0, no tree ops */
                __mem_cgroup_insert_exceeded(mz, mctz, excess);
                spin_unlock_irq(&mctz->lock);
                css_put(&mz->memcg->css);
                loop++;
                /*
                 * Could not reclaim anything and there are no more
                 * mem cgroups to try or we seem to be looping without
                 * reclaiming anything.
                 */
                if (!nr_reclaimed &&
                        (next_mz == NULL ||
                        loop > MEM_CGROUP_MAX_SOFT_LIMIT_RECLAIM_LOOPS))
                        break;
        } while (!nr_reclaimed);
        if (next_mz)
                css_put(&next_mz->memcg->css);
        return nr_reclaimed;
}

/*
 * Test whether @memcg has children, dead or alive.  Note that this
 * function doesn't care whether @memcg has use_hierarchy enabled and
 * returns %true if there are child csses according to the cgroup
 * hierarchy.  Testing use_hierarchy is the caller's responsiblity.
 */
static inline bool memcg_has_children(struct mem_cgroup *memcg)
{
        bool ret;

        /*
         * The lock does not prevent addition or deletion of children, but
         * it prevents a new child from being initialized based on this
         * parent in css_online(), so it's enough to decide whether
         * hierarchically inherited attributes can still be changed or not.
         */
        lockdep_assert_held(&memcg_create_mutex);

        rcu_read_lock();
        ret = css_next_child(NULL, &memcg->css);
        rcu_read_unlock();
        return ret;
}

/*
 * Reclaims as many pages from the given memcg as possible and moves
 * the rest to the parent.
 *
 * Caller is responsible for holding css reference for memcg.
 */
static int mem_cgroup_force_empty(struct mem_cgroup *memcg)
{
        int nr_retries = MEM_CGROUP_RECLAIM_RETRIES;

        /* we call try-to-free pages for make this cgroup empty */
        lru_add_drain_all();
        /* try to free all pages in this cgroup */
        while (nr_retries && page_counter_read(&memcg->memory)) {
                int progress;

                if (signal_pending(current))
                        return -EINTR;

                progress = try_to_free_mem_cgroup_pages(memcg, 1,
                                                        GFP_KERNEL, true);
                if (!progress) {
                        nr_retries--;
                        /* maybe some writeback is necessary */
                        congestion_wait(BLK_RW_ASYNC, HZ/10);
                }

        }

        return 0;
}

static ssize_t mem_cgroup_force_empty_write(struct kernfs_open_file *of,
                                            char *buf, size_t nbytes,
                                            loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));

        if (mem_cgroup_is_root(memcg))
                return -EINVAL;
        return mem_cgroup_force_empty(memcg) ?: nbytes;
}

static u64 mem_cgroup_hierarchy_read(struct cgroup_subsys_state *css,
                                     struct cftype *cft)
{
        return mem_cgroup_from_css(css)->use_hierarchy;
}

static int mem_cgroup_hierarchy_write(struct cgroup_subsys_state *css,
                                      struct cftype *cft, u64 val)
{
        int retval = 0;
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent_memcg = mem_cgroup_from_css(memcg->css.parent);

        mutex_lock(&memcg_create_mutex);

        if (memcg->use_hierarchy == val)
                goto out;

        /*
         * If parent's use_hierarchy is set, we can't make any modifications
         * in the child subtrees. If it is unset, then the change can
         * occur, provided the current cgroup has no children.
         *
         * For the root cgroup, parent_mem is NULL, we allow value to be
         * set if there are no children.
         */
        if ((!parent_memcg || !parent_memcg->use_hierarchy) &&
                                (val == 1 || val == 0)) {
                if (!memcg_has_children(memcg))
                        memcg->use_hierarchy = val;
                else
                        retval = -EBUSY;
        } else
                retval = -EINVAL;

out:
        mutex_unlock(&memcg_create_mutex);

        return retval;
}

static unsigned long tree_stat(struct mem_cgroup *memcg,
                               enum mem_cgroup_stat_index idx)
{
        struct mem_cgroup *iter;
        long val = 0;

        /* Per-cpu values can be negative, use a signed accumulator */
        for_each_mem_cgroup_tree(iter, memcg)
                val += mem_cgroup_read_stat(iter, idx);

        if (val < 0) /* race ? */
                val = 0;
        return val;
}

static inline u64 mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
{
        u64 val;

        if (mem_cgroup_is_root(memcg)) {
                val = tree_stat(memcg, MEM_CGROUP_STAT_CACHE);
                val += tree_stat(memcg, MEM_CGROUP_STAT_RSS);
                if (swap)
                        val += tree_stat(memcg, MEM_CGROUP_STAT_SWAP);
        } else {
                if (!swap)
                        val = page_counter_read(&memcg->memory);
                else
                        val = page_counter_read(&memcg->memsw);
        }
        return val << PAGE_SHIFT;
}

enum {
        RES_USAGE,
        RES_LIMIT,
        RES_MAX_USAGE,
        RES_FAILCNT,
        RES_SOFT_LIMIT,
};

static u64 mem_cgroup_read_u64(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct page_counter *counter;

        switch (MEMFILE_TYPE(cft->private)) {
        case _MEM:
                counter = &memcg->memory;
                break;
        case _MEMSWAP:
                counter = &memcg->memsw;
                break;
        case _KMEM:
                counter = &memcg->kmem;
                break;
        default:
                BUG();
        }

        switch (MEMFILE_ATTR(cft->private)) {
        case RES_USAGE:
                if (counter == &memcg->memory)
                        return mem_cgroup_usage(memcg, false);
                if (counter == &memcg->memsw)
                        return mem_cgroup_usage(memcg, true);
                return (u64)page_counter_read(counter) * PAGE_SIZE;
        case RES_LIMIT:
                return (u64)counter->limit * PAGE_SIZE;
        case RES_MAX_USAGE:
                return (u64)counter->watermark * PAGE_SIZE;
        case RES_FAILCNT:
                return counter->failcnt;
        case RES_SOFT_LIMIT:
                return (u64)memcg->soft_limit * PAGE_SIZE;
        default:
                BUG();
        }
}

#ifdef CONFIG_MEMCG_KMEM
static int memcg_activate_kmem(struct mem_cgroup *memcg,
                               unsigned long nr_pages)
{
        int err = 0;
        int memcg_id;

        if (memcg_kmem_is_active(memcg))
                return 0;

        /*
         * For simplicity, we won't allow this to be disabled.  It also can't
         * be changed if the cgroup has children already, or if tasks had
         * already joined.
         *
         * If tasks join before we set the limit, a person looking at
         * kmem.usage_in_bytes will have no way to determine when it took
         * place, which makes the value quite meaningless.
         *
         * After it first became limited, changes in the value of the limit are
         * of course permitted.
         */
        mutex_lock(&memcg_create_mutex);
        if (cgroup_has_tasks(memcg->css.cgroup) ||
            (memcg->use_hierarchy && memcg_has_children(memcg)))
                err = -EBUSY;
        mutex_unlock(&memcg_create_mutex);
        if (err)
                goto out;

        memcg_id = memcg_alloc_cache_id();
        if (memcg_id < 0) {
                err = memcg_id;
                goto out;
        }

        /*
         * We couldn't have accounted to this cgroup, because it hasn't got
         * activated yet, so this should succeed.
         */
        err = page_counter_limit(&memcg->kmem, nr_pages);
        VM_BUG_ON(err);

        static_key_slow_inc(&memcg_kmem_enabled_key);
        /*
         * A memory cgroup is considered kmem-active as soon as it gets
         * kmemcg_id. Setting the id after enabling static branching will
         * guarantee no one starts accounting before all call sites are
         * patched.
         */
        memcg->kmemcg_id = memcg_id;
out:
        return err;
}

static int memcg_update_kmem_limit(struct mem_cgroup *memcg,
                                   unsigned long limit)
{
        int ret;

        mutex_lock(&memcg_limit_mutex);
        if (!memcg_kmem_is_active(memcg))
                ret = memcg_activate_kmem(memcg, limit);
        else
                ret = page_counter_limit(&memcg->kmem, limit);
        mutex_unlock(&memcg_limit_mutex);
        return ret;
}

static int memcg_propagate_kmem(struct mem_cgroup *memcg)
{
        int ret = 0;
        struct mem_cgroup *parent = parent_mem_cgroup(memcg);

        if (!parent)
                return 0;

        mutex_lock(&memcg_limit_mutex);
        /*
         * If the parent cgroup is not kmem-active now, it cannot be activated
         * after this point, because it has at least one child already.
         */
        if (memcg_kmem_is_active(parent))
                ret = memcg_activate_kmem(memcg, PAGE_COUNTER_MAX);
        mutex_unlock(&memcg_limit_mutex);
        return ret;
}
#else
static int memcg_update_kmem_limit(struct mem_cgroup *memcg,
                                   unsigned long limit)
{
        return -EINVAL;
}
#endif /* CONFIG_MEMCG_KMEM */

/*
 * The user of this function is...
 * RES_LIMIT.
 */
static ssize_t mem_cgroup_write(struct kernfs_open_file *of,
                                char *buf, size_t nbytes, loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
        unsigned long nr_pages;
        int ret;

        buf = strstrip(buf);
        ret = page_counter_memparse(buf, "-1", &nr_pages);
        if (ret)
                return ret;

        switch (MEMFILE_ATTR(of_cft(of)->private)) {
        case RES_LIMIT:
                if (mem_cgroup_is_root(memcg)) { /* Can't set limit on root */
                        ret = -EINVAL;
                        break;
                }
                switch (MEMFILE_TYPE(of_cft(of)->private)) {
                case _MEM:
                        ret = mem_cgroup_resize_limit(memcg, nr_pages);
                        break;
                case _MEMSWAP:
                        ret = mem_cgroup_resize_memsw_limit(memcg, nr_pages);
                        break;
                case _KMEM:
                        ret = memcg_update_kmem_limit(memcg, nr_pages);
                        break;
                }
                break;
        case RES_SOFT_LIMIT:
                memcg->soft_limit = nr_pages;
                ret = 0;
                break;
        }
        return ret ?: nbytes;
}

static ssize_t mem_cgroup_reset(struct kernfs_open_file *of, char *buf,
                                size_t nbytes, loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
        struct page_counter *counter;

        switch (MEMFILE_TYPE(of_cft(of)->private)) {
        case _MEM:
                counter = &memcg->memory;
                break;
        case _MEMSWAP:
                counter = &memcg->memsw;
                break;
        case _KMEM:
                counter = &memcg->kmem;
                break;
        default:
                BUG();
        }

        switch (MEMFILE_ATTR(of_cft(of)->private)) {
        case RES_MAX_USAGE:
                page_counter_reset_watermark(counter);
                break;
        case RES_FAILCNT:
                counter->failcnt = 0;
                break;
        default:
                BUG();
        }

        return nbytes;
}

static u64 mem_cgroup_move_charge_read(struct cgroup_subsys_state *css,
                                        struct cftype *cft)
{
        return mem_cgroup_from_css(css)->move_charge_at_immigrate;
}

#ifdef CONFIG_MMU
static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
                                        struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        if (val & ~MOVE_MASK)
                return -EINVAL;

        /*
         * No kind of locking is needed in here, because ->can_attach() will
         * check this value once in the beginning of the process, and then carry
         * on with stale data. This means that changes to this value will only
         * affect task migrations starting after the change.
         */
        memcg->move_charge_at_immigrate = val;
        return 0;
}
#else
static int mem_cgroup_move_charge_write(struct cgroup_subsys_state *css,
                                        struct cftype *cft, u64 val)
{
        return -ENOSYS;
}
#endif

#ifdef CONFIG_NUMA
static int memcg_numa_stat_show(struct seq_file *m, void *v)
{
        struct numa_stat {
                const char *name;
                unsigned int lru_mask;
        };

        static const struct numa_stat stats[] = {
                { "total", LRU_ALL },
                { "file", LRU_ALL_FILE },
                { "anon", LRU_ALL_ANON },
                { "unevictable", BIT(LRU_UNEVICTABLE) },
        };
        const struct numa_stat *stat;
        int nid;
        unsigned long nr;
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));

        for (stat = stats; stat < stats + ARRAY_SIZE(stats); stat++) {
                nr = mem_cgroup_nr_lru_pages(memcg, stat->lru_mask);
                seq_printf(m, "%s=%lu", stat->name, nr);
                for_each_node_state(nid, N_MEMORY) {
                        nr = mem_cgroup_node_nr_lru_pages(memcg, nid,
                                                          stat->lru_mask);
                        seq_printf(m, " N%d=%lu", nid, nr);
                }
                seq_putc(m, '\n');
        }

        for (stat = stats; stat < stats + ARRAY_SIZE(stats); stat++) {
                struct mem_cgroup *iter;

                nr = 0;
                for_each_mem_cgroup_tree(iter, memcg)
                        nr += mem_cgroup_nr_lru_pages(iter, stat->lru_mask);
                seq_printf(m, "hierarchical_%s=%lu", stat->name, nr);
                for_each_node_state(nid, N_MEMORY) {
                        nr = 0;
                        for_each_mem_cgroup_tree(iter, memcg)
                                nr += mem_cgroup_node_nr_lru_pages(
                                        iter, nid, stat->lru_mask);
                        seq_printf(m, " N%d=%lu", nid, nr);
                }
                seq_putc(m, '\n');
        }

        return 0;
}
#endif /* CONFIG_NUMA */

static int memcg_stat_show(struct seq_file *m, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
        unsigned long memory, memsw;
        struct mem_cgroup *mi;
        unsigned int i;

        BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_stat_names) !=
                     MEM_CGROUP_STAT_NSTATS);
        BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_events_names) !=
                     MEM_CGROUP_EVENTS_NSTATS);
        BUILD_BUG_ON(ARRAY_SIZE(mem_cgroup_lru_names) != NR_LRU_LISTS);

        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                        continue;
                seq_printf(m, "%s %ld\n", mem_cgroup_stat_names[i],
                           mem_cgroup_read_stat(memcg, i) * PAGE_SIZE);
        }

        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++)
                seq_printf(m, "%s %lu\n", mem_cgroup_events_names[i],
                           mem_cgroup_read_events(memcg, i));

        for (i = 0; i < NR_LRU_LISTS; i++)
                seq_printf(m, "%s %lu\n", mem_cgroup_lru_names[i],
                           mem_cgroup_nr_lru_pages(memcg, BIT(i)) * PAGE_SIZE);

        /* Hierarchical information */
        memory = memsw = PAGE_COUNTER_MAX;
        for (mi = memcg; mi; mi = parent_mem_cgroup(mi)) {
                memory = min(memory, mi->memory.limit);
                memsw = min(memsw, mi->memsw.limit);
        }
        seq_printf(m, "hierarchical_memory_limit %llu\n",
                   (u64)memory * PAGE_SIZE);
        if (do_swap_account)
                seq_printf(m, "hierarchical_memsw_limit %llu\n",
                           (u64)memsw * PAGE_SIZE);

        for (i = 0; i < MEM_CGROUP_STAT_NSTATS; i++) {
                long long val = 0;

                if (i == MEM_CGROUP_STAT_SWAP && !do_swap_account)
                        continue;
                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_read_stat(mi, i) * PAGE_SIZE;
                seq_printf(m, "total_%s %lld\n", mem_cgroup_stat_names[i], val);
        }

        for (i = 0; i < MEM_CGROUP_EVENTS_NSTATS; i++) {
                unsigned long long val = 0;

                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_read_events(mi, i);
                seq_printf(m, "total_%s %llu\n",
                           mem_cgroup_events_names[i], val);
        }

        for (i = 0; i < NR_LRU_LISTS; i++) {
                unsigned long long val = 0;

                for_each_mem_cgroup_tree(mi, memcg)
                        val += mem_cgroup_nr_lru_pages(mi, BIT(i)) * PAGE_SIZE;
                seq_printf(m, "total_%s %llu\n", mem_cgroup_lru_names[i], val);
        }

#ifdef CONFIG_DEBUG_VM
        {
                int nid, zid;
                struct mem_cgroup_per_zone *mz;
                struct zone_reclaim_stat *rstat;
                unsigned long recent_rotated[2] = {0, 0};
                unsigned long recent_scanned[2] = {0, 0};

                for_each_online_node(nid)
                        for (zid = 0; zid < MAX_NR_ZONES; zid++) {
                                mz = &memcg->nodeinfo[nid]->zoneinfo[zid];
                                rstat = &mz->lruvec.reclaim_stat;

                                recent_rotated[0] += rstat->recent_rotated[0];
                                recent_rotated[1] += rstat->recent_rotated[1];
                                recent_scanned[0] += rstat->recent_scanned[0];
                                recent_scanned[1] += rstat->recent_scanned[1];
                        }
                seq_printf(m, "recent_rotated_anon %lu\n", recent_rotated[0]);
                seq_printf(m, "recent_rotated_file %lu\n", recent_rotated[1]);
                seq_printf(m, "recent_scanned_anon %lu\n", recent_scanned[0]);
                seq_printf(m, "recent_scanned_file %lu\n", recent_scanned[1]);
        }
#endif

        return 0;
}

static u64 mem_cgroup_swappiness_read(struct cgroup_subsys_state *css,
                                      struct cftype *cft)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        return mem_cgroup_swappiness(memcg);
}

static int mem_cgroup_swappiness_write(struct cgroup_subsys_state *css,
                                       struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        if (val > 100)
                return -EINVAL;

        if (css->parent)
                memcg->swappiness = val;
        else
                vm_swappiness = val;

        return 0;
}

static void __mem_cgroup_threshold(struct mem_cgroup *memcg, bool swap)
{
        struct mem_cgroup_threshold_ary *t;
        unsigned long usage;
        int i;

        rcu_read_lock();
        if (!swap)
                t = rcu_dereference(memcg->thresholds.primary);
        else
                t = rcu_dereference(memcg->memsw_thresholds.primary);

        if (!t)
                goto unlock;

        usage = mem_cgroup_usage(memcg, swap);

        /*
         * current_threshold points to threshold just below or equal to usage.
         * If it's not true, a threshold was crossed after last
         * call of __mem_cgroup_threshold().
         */
        i = t->current_threshold;

        /*
         * Iterate backward over array of thresholds starting from
         * current_threshold and check if a threshold is crossed.
         * If none of thresholds below usage is crossed, we read
         * only one element of the array here.
         */
        for (; i >= 0 && unlikely(t->entries[i].threshold > usage); i--)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* i = current_threshold + 1 */
        i++;

        /*
         * Iterate forward over array of thresholds starting from
         * current_threshold+1 and check if a threshold is crossed.
         * If none of thresholds above usage is crossed, we read
         * only one element of the array here.
         */
        for (; i < t->size && unlikely(t->entries[i].threshold <= usage); i++)
                eventfd_signal(t->entries[i].eventfd, 1);

        /* Update current_threshold */
        t->current_threshold = i - 1;
unlock:
        rcu_read_unlock();
}

static void mem_cgroup_threshold(struct mem_cgroup *memcg)
{
        while (memcg) {
                __mem_cgroup_threshold(memcg, false);
                if (do_swap_account)
                        __mem_cgroup_threshold(memcg, true);

                memcg = parent_mem_cgroup(memcg);
        }
}

static int compare_thresholds(const void *a, const void *b)
{
        const struct mem_cgroup_threshold *_a = a;
        const struct mem_cgroup_threshold *_b = b;

        if (_a->threshold > _b->threshold)
                return 1;

        if (_a->threshold < _b->threshold)
                return -1;

        return 0;
}

static int mem_cgroup_oom_notify_cb(struct mem_cgroup *memcg)
{
        struct mem_cgroup_eventfd_list *ev;

        spin_lock(&memcg_oom_lock);

        list_for_each_entry(ev, &memcg->oom_notify, list)
                eventfd_signal(ev->eventfd, 1);

        spin_unlock(&memcg_oom_lock);
        return 0;
}

static void mem_cgroup_oom_notify(struct mem_cgroup *memcg)
{
        struct mem_cgroup *iter;

        for_each_mem_cgroup_tree(iter, memcg)
                mem_cgroup_oom_notify_cb(iter);
}

static int __mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd, const char *args, enum res_type type)
{
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        unsigned long threshold;
        unsigned long usage;
        int i, size, ret;

        ret = page_counter_memparse(args, "-1", &threshold);
        if (ret)
                return ret;

        mutex_lock(&memcg->thresholds_lock);

        if (type == _MEM) {
                thresholds = &memcg->thresholds;
                usage = mem_cgroup_usage(memcg, false);
        } else if (type == _MEMSWAP) {
                thresholds = &memcg->memsw_thresholds;
                usage = mem_cgroup_usage(memcg, true);
        } else
                BUG();

        /* Check if a threshold crossed before adding a new one */
        if (thresholds->primary)
                __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        size = thresholds->primary ? thresholds->primary->size + 1 : 1;

        /* Allocate memory for new array of thresholds */
        new = kmalloc(sizeof(*new) + size * sizeof(struct mem_cgroup_threshold),
                        GFP_KERNEL);
        if (!new) {
                ret = -ENOMEM;
                goto unlock;
        }
        new->size = size;

        /* Copy thresholds (if any) to new array */
        if (thresholds->primary) {
                memcpy(new->entries, thresholds->primary->entries, (size - 1) *
                                sizeof(struct mem_cgroup_threshold));
        }

        /* Add new threshold */
        new->entries[size - 1].eventfd = eventfd;
        new->entries[size - 1].threshold = threshold;

        /* Sort thresholds. Registering of new threshold isn't time-critical */
        sort(new->entries, size, sizeof(struct mem_cgroup_threshold),
                        compare_thresholds, NULL);

        /* Find current threshold */
        new->current_threshold = -1;
        for (i = 0; i < size; i++) {
                if (new->entries[i].threshold <= usage) {
                        /*
                         * new->current_threshold will not be used until
                         * rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                } else
                        break;
        }

        /* Free old spare buffer and save old primary buffer as spare */
        kfree(thresholds->spare);
        thresholds->spare = thresholds->primary;

        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();

unlock:
        mutex_unlock(&memcg->thresholds_lock);

        return ret;
}

static int mem_cgroup_usage_register_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd, const char *args)
{
        return __mem_cgroup_usage_register_event(memcg, eventfd, args, _MEM);
}

static int memsw_cgroup_usage_register_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd, const char *args)
{
        return __mem_cgroup_usage_register_event(memcg, eventfd, args, _MEMSWAP);
}

static void __mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd, enum res_type type)
{
        struct mem_cgroup_thresholds *thresholds;
        struct mem_cgroup_threshold_ary *new;
        unsigned long usage;
        int i, j, size;

        mutex_lock(&memcg->thresholds_lock);

        if (type == _MEM) {
                thresholds = &memcg->thresholds;
                usage = mem_cgroup_usage(memcg, false);
        } else if (type == _MEMSWAP) {
                thresholds = &memcg->memsw_thresholds;
                usage = mem_cgroup_usage(memcg, true);
        } else
                BUG();

        if (!thresholds->primary)
                goto unlock;

        /* Check if a threshold crossed before removing */
        __mem_cgroup_threshold(memcg, type == _MEMSWAP);

        /* Calculate new number of threshold */
        size = 0;
        for (i = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd != eventfd)
                        size++;
        }

        new = thresholds->spare;

        /* Set thresholds array to NULL if we don't have thresholds */
        if (!size) {
                kfree(new);
                new = NULL;
                goto swap_buffers;
        }

        new->size = size;

        /* Copy thresholds and find current threshold */
        new->current_threshold = -1;
        for (i = 0, j = 0; i < thresholds->primary->size; i++) {
                if (thresholds->primary->entries[i].eventfd == eventfd)
                        continue;

                new->entries[j] = thresholds->primary->entries[i];
                if (new->entries[j].threshold <= usage) {
                        /*
                         * new->current_threshold will not be used
                         * until rcu_assign_pointer(), so it's safe to increment
                         * it here.
                         */
                        ++new->current_threshold;
                }
                j++;
        }

swap_buffers:
        /* Swap primary and spare array */
        thresholds->spare = thresholds->primary;
        /* If all events are unregistered, free the spare array */
        if (!new) {
                kfree(thresholds->spare);
                thresholds->spare = NULL;
        }

        rcu_assign_pointer(thresholds->primary, new);

        /* To be sure that nobody uses thresholds */
        synchronize_rcu();
unlock:
        mutex_unlock(&memcg->thresholds_lock);
}

static void mem_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd)
{
        return __mem_cgroup_usage_unregister_event(memcg, eventfd, _MEM);
}

static void memsw_cgroup_usage_unregister_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd)
{
        return __mem_cgroup_usage_unregister_event(memcg, eventfd, _MEMSWAP);
}

static int mem_cgroup_oom_register_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd, const char *args)
{
        struct mem_cgroup_eventfd_list *event;

        event = kmalloc(sizeof(*event), GFP_KERNEL);
        if (!event)
                return -ENOMEM;

        spin_lock(&memcg_oom_lock);

        event->eventfd = eventfd;
        list_add(&event->list, &memcg->oom_notify);

        /* already in OOM ? */
        if (atomic_read(&memcg->under_oom))
                eventfd_signal(eventfd, 1);
        spin_unlock(&memcg_oom_lock);

        return 0;
}

static void mem_cgroup_oom_unregister_event(struct mem_cgroup *memcg,
        struct eventfd_ctx *eventfd)
{
        struct mem_cgroup_eventfd_list *ev, *tmp;

        spin_lock(&memcg_oom_lock);

        list_for_each_entry_safe(ev, tmp, &memcg->oom_notify, list) {
                if (ev->eventfd == eventfd) {
                        list_del(&ev->list);
                        kfree(ev);
                }
        }

        spin_unlock(&memcg_oom_lock);
}

static int mem_cgroup_oom_control_read(struct seq_file *sf, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(sf));

        seq_printf(sf, "oom_kill_disable %d\n", memcg->oom_kill_disable);
        seq_printf(sf, "under_oom %d\n", (bool)atomic_read(&memcg->under_oom));
        return 0;
}

static int mem_cgroup_oom_control_write(struct cgroup_subsys_state *css,
        struct cftype *cft, u64 val)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        /* cannot set to root cgroup and only 0 and 1 are allowed */
        if (!css->parent || !((val == 0) || (val == 1)))
                return -EINVAL;

        memcg->oom_kill_disable = val;
        if (!val)
                memcg_oom_recover(memcg);

        return 0;
}

#ifdef CONFIG_MEMCG_KMEM
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
        int ret;

        ret = memcg_propagate_kmem(memcg);
        if (ret)
                return ret;

        return mem_cgroup_sockets_init(memcg, ss);
}

static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
        memcg_destroy_kmem_caches(memcg);
        mem_cgroup_sockets_destroy(memcg);
}
#else
static int memcg_init_kmem(struct mem_cgroup *memcg, struct cgroup_subsys *ss)
{
        return 0;
}

static void memcg_destroy_kmem(struct mem_cgroup *memcg)
{
}
#endif

/*
 * DO NOT USE IN NEW FILES.
 *
 * "cgroup.event_control" implementation.
 *
 * This is way over-engineered.  It tries to support fully configurable
 * events for each user.  Such level of flexibility is completely
 * unnecessary especially in the light of the planned unified hierarchy.
 *
 * Please deprecate this and replace with something simpler if at all
 * possible.
 */

/*
 * Unregister event and free resources.
 *
 * Gets called from workqueue.
 */
static void memcg_event_remove(struct work_struct *work)
{
        struct mem_cgroup_event *event =
                container_of(work, struct mem_cgroup_event, remove);
        struct mem_cgroup *memcg = event->memcg;

        remove_wait_queue(event->wqh, &event->wait);

        event->unregister_event(memcg, event->eventfd);

        /* Notify userspace the event is going away. */
        eventfd_signal(event->eventfd, 1);

        eventfd_ctx_put(event->eventfd);
        kfree(event);
        css_put(&memcg->css);
}

/*
 * Gets called on POLLHUP on eventfd when user closes it.
 *
 * Called with wqh->lock held and interrupts disabled.
 */
static int memcg_event_wake(wait_queue_t *wait, unsigned mode,
                            int sync, void *key)
{
        struct mem_cgroup_event *event =
                container_of(wait, struct mem_cgroup_event, wait);
        struct mem_cgroup *memcg = event->memcg;
        unsigned long flags = (unsigned long)key;

        if (flags & POLLHUP) {
                /*
                 * If the event has been detached at cgroup removal, we
                 * can simply return knowing the other side will cleanup
                 * for us.
                 *
                 * We can't race against event freeing since the other
                 * side will require wqh->lock via remove_wait_queue(),
                 * which we hold.
                 */
                spin_lock(&memcg->event_list_lock);
                if (!list_empty(&event->list)) {
                        list_del_init(&event->list);
                        /*
                         * We are in atomic context, but cgroup_event_remove()
                         * may sleep, so we have to call it in workqueue.
                         */
                        schedule_work(&event->remove);
                }
                spin_unlock(&memcg->event_list_lock);
        }

        return 0;
}

static void memcg_event_ptable_queue_proc(struct file *file,
                wait_queue_head_t *wqh, poll_table *pt)
{
        struct mem_cgroup_event *event =
                container_of(pt, struct mem_cgroup_event, pt);

        event->wqh = wqh;
        add_wait_queue(wqh, &event->wait);
}

/*
 * DO NOT USE IN NEW FILES.
 *
 * Parse input and register new cgroup event handler.
 *
 * Input must be in format '<event_fd> <control_fd> <args>'.
 * Interpretation of args is defined by control file implementation.
 */
static ssize_t memcg_write_event_control(struct kernfs_open_file *of,
                                         char *buf, size_t nbytes, loff_t off)
{
        struct cgroup_subsys_state *css = of_css(of);
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_event *event;
        struct cgroup_subsys_state *cfile_css;
        unsigned int efd, cfd;
        struct fd efile;
        struct fd cfile;
        const char *name;
        char *endp;
        int ret;

        buf = strstrip(buf);

        efd = simple_strtoul(buf, &endp, 10);
        if (*endp != ' ')
                return -EINVAL;
        buf = endp + 1;

        cfd = simple_strtoul(buf, &endp, 10);
        if ((*endp != ' ') && (*endp != '\0'))
                return -EINVAL;
        buf = endp + 1;

        event = kzalloc(sizeof(*event), GFP_KERNEL);
        if (!event)
                return -ENOMEM;

        event->memcg = memcg;
        INIT_LIST_HEAD(&event->list);
        init_poll_funcptr(&event->pt, memcg_event_ptable_queue_proc);
        init_waitqueue_func_entry(&event->wait, memcg_event_wake);
        INIT_WORK(&event->remove, memcg_event_remove);

        efile = fdget(efd);
        if (!efile.file) {
                ret = -EBADF;
                goto out_kfree;
        }

        event->eventfd = eventfd_ctx_fileget(efile.file);
        if (IS_ERR(event->eventfd)) {
                ret = PTR_ERR(event->eventfd);
                goto out_put_efile;
        }

        cfile = fdget(cfd);
        if (!cfile.file) {
                ret = -EBADF;
                goto out_put_eventfd;
        }

        /* the process need read permission on control file */
        /* AV: shouldn't we check that it's been opened for read instead? */
        ret = inode_permission(file_inode(cfile.file), MAY_READ);
        if (ret < 0)
                goto out_put_cfile;

        /*
         * Determine the event callbacks and set them in @event.  This used
         * to be done via struct cftype but cgroup core no longer knows
         * about these events.  The following is crude but the whole thing
         * is for compatibility anyway.
         *
         * DO NOT ADD NEW FILES.
         */
        name = cfile.file->f_path.dentry->d_name.name;

        if (!strcmp(name, "memory.usage_in_bytes")) {
                event->register_event = mem_cgroup_usage_register_event;
                event->unregister_event = mem_cgroup_usage_unregister_event;
        } else if (!strcmp(name, "memory.oom_control")) {
                event->register_event = mem_cgroup_oom_register_event;
                event->unregister_event = mem_cgroup_oom_unregister_event;
        } else if (!strcmp(name, "memory.pressure_level")) {
                event->register_event = vmpressure_register_event;
                event->unregister_event = vmpressure_unregister_event;
        } else if (!strcmp(name, "memory.memsw.usage_in_bytes")) {
                event->register_event = memsw_cgroup_usage_register_event;
                event->unregister_event = memsw_cgroup_usage_unregister_event;
        } else {
                ret = -EINVAL;
                goto out_put_cfile;
        }

        /*
         * Verify @cfile should belong to @css.  Also, remaining events are
         * automatically removed on cgroup destruction but the removal is
         * asynchronous, so take an extra ref on @css.
         */
        cfile_css = css_tryget_online_from_dir(cfile.file->f_path.dentry->d_parent,
                                               &memory_cgrp_subsys);
        ret = -EINVAL;
        if (IS_ERR(cfile_css))
                goto out_put_cfile;
        if (cfile_css != css) {
                css_put(cfile_css);
                goto out_put_cfile;
        }

        ret = event->register_event(memcg, event->eventfd, buf);
        if (ret)
                goto out_put_css;

        efile.file->f_op->poll(efile.file, &event->pt);

        spin_lock(&memcg->event_list_lock);
        list_add(&event->list, &memcg->event_list);
        spin_unlock(&memcg->event_list_lock);

        fdput(cfile);
        fdput(efile);

        return nbytes;

out_put_css:
        css_put(css);
out_put_cfile:
        fdput(cfile);
out_put_eventfd:
        eventfd_ctx_put(event->eventfd);
out_put_efile:
        fdput(efile);
out_kfree:
        kfree(event);

        return ret;
}

static struct cftype mem_cgroup_legacy_files[] = {
        {
                .name = "usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_USAGE),
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_MAX_USAGE),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_LIMIT),
                .write = mem_cgroup_write,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "soft_limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEM, RES_SOFT_LIMIT),
                .write = mem_cgroup_write,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "failcnt",
                .private = MEMFILE_PRIVATE(_MEM, RES_FAILCNT),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "stat",
                .seq_show = memcg_stat_show,
        },
        {
                .name = "force_empty",
                .write = mem_cgroup_force_empty_write,
        },
        {
                .name = "use_hierarchy",
                .write_u64 = mem_cgroup_hierarchy_write,
                .read_u64 = mem_cgroup_hierarchy_read,
        },
        {
                .name = "cgroup.event_control",         /* XXX: for compat */
                .write = memcg_write_event_control,
                .flags = CFTYPE_NO_PREFIX,
                .mode = S_IWUGO,
        },
        {
                .name = "swappiness",
                .read_u64 = mem_cgroup_swappiness_read,
                .write_u64 = mem_cgroup_swappiness_write,
        },
        {
                .name = "move_charge_at_immigrate",
                .read_u64 = mem_cgroup_move_charge_read,
                .write_u64 = mem_cgroup_move_charge_write,
        },
        {
                .name = "oom_control",
                .seq_show = mem_cgroup_oom_control_read,
                .write_u64 = mem_cgroup_oom_control_write,
                .private = MEMFILE_PRIVATE(_OOM_TYPE, OOM_CONTROL),
        },
        {
                .name = "pressure_level",
        },
#ifdef CONFIG_NUMA
        {
                .name = "numa_stat",
                .seq_show = memcg_numa_stat_show,
        },
#endif
#ifdef CONFIG_MEMCG_KMEM
        {
                .name = "kmem.limit_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_LIMIT),
                .write = mem_cgroup_write,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "kmem.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_USAGE),
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "kmem.failcnt",
                .private = MEMFILE_PRIVATE(_KMEM, RES_FAILCNT),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "kmem.max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_KMEM, RES_MAX_USAGE),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
#ifdef CONFIG_SLABINFO
        {
                .name = "kmem.slabinfo",
                .seq_start = slab_start,
                .seq_next = slab_next,
                .seq_stop = slab_stop,
                .seq_show = memcg_slab_show,
        },
#endif
#endif
        { },    /* terminate */
};

#ifdef CONFIG_MEMCG_SWAP
static struct cftype memsw_cgroup_files[] = {
        {
                .name = "memsw.usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_USAGE),
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "memsw.max_usage_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_MAX_USAGE),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "memsw.limit_in_bytes",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_LIMIT),
                .write = mem_cgroup_write,
                .read_u64 = mem_cgroup_read_u64,
        },
        {
                .name = "memsw.failcnt",
                .private = MEMFILE_PRIVATE(_MEMSWAP, RES_FAILCNT),
                .write = mem_cgroup_reset,
                .read_u64 = mem_cgroup_read_u64,
        },
        { },    /* terminate */
};
#endif
static int alloc_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
{
        struct mem_cgroup_per_node *pn;
        struct mem_cgroup_per_zone *mz;
        int zone, tmp = node;
        /*
         * This routine is called against possible nodes.
         * But it's BUG to call kmalloc() against offline node.
         *
         * TODO: this routine can waste much memory for nodes which will
         *       never be onlined. It's better to use memory hotplug callback
         *       function.
         */
        if (!node_state(node, N_NORMAL_MEMORY))
                tmp = -1;
        pn = kzalloc_node(sizeof(*pn), GFP_KERNEL, tmp);
        if (!pn)
                return 1;

        for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                mz = &pn->zoneinfo[zone];
                lruvec_init(&mz->lruvec);
                mz->usage_in_excess = 0;
                mz->on_tree = false;
                mz->memcg = memcg;
        }
        memcg->nodeinfo[node] = pn;
        return 0;
}

static void free_mem_cgroup_per_zone_info(struct mem_cgroup *memcg, int node)
{
        kfree(memcg->nodeinfo[node]);
}

static struct mem_cgroup *mem_cgroup_alloc(void)
{
        struct mem_cgroup *memcg;
        size_t size;

        size = sizeof(struct mem_cgroup);
        size += nr_node_ids * sizeof(struct mem_cgroup_per_node *);

        memcg = kzalloc(size, GFP_KERNEL);
        if (!memcg)
                return NULL;

        memcg->stat = alloc_percpu(struct mem_cgroup_stat_cpu);
        if (!memcg->stat)
                goto out_free;
        spin_lock_init(&memcg->pcp_counter_lock);
        return memcg;

out_free:
        kfree(memcg);
        return NULL;
}

/*
 * At destroying mem_cgroup, references from swap_cgroup can remain.
 * (scanning all at force_empty is too costly...)
 *
 * Instead of clearing all references at force_empty, we remember
 * the number of reference from swap_cgroup and free mem_cgroup when
 * it goes down to 0.
 *
 * Removal of cgroup itself succeeds regardless of refs from swap.
 */

static void __mem_cgroup_free(struct mem_cgroup *memcg)
{
        int node;

        mem_cgroup_remove_from_trees(memcg);

        for_each_node(node)
                free_mem_cgroup_per_zone_info(memcg, node);

        free_percpu(memcg->stat);

        disarm_static_keys(memcg);
        kfree(memcg);
}

/*
 * Returns the parent mem_cgroup in memcgroup hierarchy with hierarchy enabled.
 */
struct mem_cgroup *parent_mem_cgroup(struct mem_cgroup *memcg)
{
        if (!memcg->memory.parent)
                return NULL;
        return mem_cgroup_from_counter(memcg->memory.parent, memory);
}
EXPORT_SYMBOL(parent_mem_cgroup);

static void __init mem_cgroup_soft_limit_tree_init(void)
{
        int node;

        for_each_node(node) {
                struct mem_cgroup_tree_per_node *rtpn;
                int zone;

                rtpn = kzalloc_node(sizeof(*rtpn), GFP_KERNEL,
                                    node_online(node) ? node : NUMA_NO_NODE);

                for (zone = 0; zone < MAX_NR_ZONES; zone++) {
                        struct mem_cgroup_tree_per_zone *rtpz;

                        rtpz = &rtpn->rb_tree_per_zone[zone];
                        rtpz->rb_root = RB_ROOT;
                        spin_lock_init(&rtpz->lock);
                }
                soft_limit_tree.rb_tree_per_node[node] = rtpn;
        }
}

static struct cgroup_subsys_state * __ref
mem_cgroup_css_alloc(struct cgroup_subsys_state *parent_css)
{
        struct mem_cgroup *memcg;
        long error = -ENOMEM;
        int node;

        memcg = mem_cgroup_alloc();
        if (!memcg)
                return ERR_PTR(error);

        for_each_node(node)
                if (alloc_mem_cgroup_per_zone_info(memcg, node))
                        goto free_out;

        /* root ? */
        if (parent_css == NULL) {
                root_mem_cgroup = memcg;
                page_counter_init(&memcg->memory, NULL);
                memcg->high = PAGE_COUNTER_MAX;
                memcg->soft_limit = PAGE_COUNTER_MAX;
                page_counter_init(&memcg->memsw, NULL);
                page_counter_init(&memcg->kmem, NULL);
        }

        memcg->last_scanned_node = MAX_NUMNODES;
        INIT_LIST_HEAD(&memcg->oom_notify);
        memcg->move_charge_at_immigrate = 0;
        mutex_init(&memcg->thresholds_lock);
        spin_lock_init(&memcg->move_lock);
        vmpressure_init(&memcg->vmpressure);
        INIT_LIST_HEAD(&memcg->event_list);
        spin_lock_init(&memcg->event_list_lock);
#ifdef CONFIG_MEMCG_KMEM
        memcg->kmemcg_id = -1;
#endif

        return &memcg->css;

free_out:
        __mem_cgroup_free(memcg);
        return ERR_PTR(error);
}

static int
mem_cgroup_css_online(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup *parent = mem_cgroup_from_css(css->parent);
        int ret;

        if (css->id > MEM_CGROUP_ID_MAX)
                return -ENOSPC;

        if (!parent)
                return 0;

        mutex_lock(&memcg_create_mutex);

        memcg->use_hierarchy = parent->use_hierarchy;
        memcg->oom_kill_disable = parent->oom_kill_disable;
        memcg->swappiness = mem_cgroup_swappiness(parent);

        if (parent->use_hierarchy) {
                page_counter_init(&memcg->memory, &parent->memory);
                memcg->high = PAGE_COUNTER_MAX;
                memcg->soft_limit = PAGE_COUNTER_MAX;
                page_counter_init(&memcg->memsw, &parent->memsw);
                page_counter_init(&memcg->kmem, &parent->kmem);

                /*
                 * No need to take a reference to the parent because cgroup
                 * core guarantees its existence.
                 */
        } else {
                page_counter_init(&memcg->memory, NULL);
                memcg->high = PAGE_COUNTER_MAX;
                memcg->soft_limit = PAGE_COUNTER_MAX;
                page_counter_init(&memcg->memsw, NULL);
                page_counter_init(&memcg->kmem, NULL);
                /*
                 * Deeper hierachy with use_hierarchy == false doesn't make
                 * much sense so let cgroup subsystem know about this
                 * unfortunate state in our controller.
                 */
                if (parent != root_mem_cgroup)
                        memory_cgrp_subsys.broken_hierarchy = true;
        }
        mutex_unlock(&memcg_create_mutex);

        ret = memcg_init_kmem(memcg, &memory_cgrp_subsys);
        if (ret)
                return ret;

        /*
         * Make sure the memcg is initialized: mem_cgroup_iter()
         * orders reading memcg->initialized against its callers
         * reading the memcg members.
         */
        smp_store_release(&memcg->initialized, 1);

        return 0;
}

static void mem_cgroup_css_offline(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        struct mem_cgroup_event *event, *tmp;

        /*
         * Unregister events and notify userspace.
         * Notify userspace about cgroup removing only after rmdir of cgroup
         * directory to avoid race between userspace and kernelspace.
         */
        spin_lock(&memcg->event_list_lock);
        list_for_each_entry_safe(event, tmp, &memcg->event_list, list) {
                list_del_init(&event->list);
                schedule_work(&event->remove);
        }
        spin_unlock(&memcg->event_list_lock);

        vmpressure_cleanup(&memcg->vmpressure);
}

static void mem_cgroup_css_free(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        memcg_destroy_kmem(memcg);
        __mem_cgroup_free(memcg);
}

/**
 * mem_cgroup_css_reset - reset the states of a mem_cgroup
 * @css: the target css
 *
 * Reset the states of the mem_cgroup associated with @css.  This is
 * invoked when the userland requests disabling on the default hierarchy
 * but the memcg is pinned through dependency.  The memcg should stop
 * applying policies and should revert to the vanilla state as it may be
 * made visible again.
 *
 * The current implementation only resets the essential configurations.
 * This needs to be expanded to cover all the visible parts.
 */
static void mem_cgroup_css_reset(struct cgroup_subsys_state *css)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);

        mem_cgroup_resize_limit(memcg, PAGE_COUNTER_MAX);
        mem_cgroup_resize_memsw_limit(memcg, PAGE_COUNTER_MAX);
        memcg_update_kmem_limit(memcg, PAGE_COUNTER_MAX);
        memcg->low = 0;
        memcg->high = PAGE_COUNTER_MAX;
        memcg->soft_limit = PAGE_COUNTER_MAX;
}

#ifdef CONFIG_MMU
/* Handlers for move charge at task migration. */
static int mem_cgroup_do_precharge(unsigned long count)
{
        int ret;

        /* Try a single bulk charge without reclaim first */
        ret = try_charge(mc.to, GFP_KERNEL & ~__GFP_WAIT, count);
        if (!ret) {
                mc.precharge += count;
                return ret;
        }
        if (ret == -EINTR) {
                cancel_charge(root_mem_cgroup, count);
                return ret;
        }

        /* Try charges one by one with reclaim */
        while (count--) {
                ret = try_charge(mc.to, GFP_KERNEL & ~__GFP_NORETRY, 1);
                /*
                 * In case of failure, any residual charges against
                 * mc.to will be dropped by mem_cgroup_clear_mc()
                 * later on.  However, cancel any charges that are
                 * bypassed to root right away or they'll be lost.
                 */
                if (ret == -EINTR)
                        cancel_charge(root_mem_cgroup, 1);
                if (ret)
                        return ret;
                mc.precharge++;
                cond_resched();
        }
        return 0;
}

/**
 * get_mctgt_type - get target type of moving charge
 * @vma: the vma the pte to be checked belongs
 * @addr: the address corresponding to the pte to be checked
 * @ptent: the pte to be checked
 * @target: the pointer the target page or swap ent will be stored(can be NULL)
 *
 * Returns
 *   0(MC_TARGET_NONE): if the pte is not a target for move charge.
 *   1(MC_TARGET_PAGE): if the page corresponding to this pte is a target for
 *     move charge. if @target is not NULL, the page is stored in target->page
 *     with extra refcnt got(Callers should handle it).
 *   2(MC_TARGET_SWAP): if the swap entry corresponding to this pte is a
 *     target for charge migration. if @target is not NULL, the entry is stored
 *     in target->ent.
 *
 * Called with pte lock held.
 */
union mc_target {
        struct page     *page;
        swp_entry_t     ent;
};

enum mc_target_type {
        MC_TARGET_NONE = 0,
        MC_TARGET_PAGE,
        MC_TARGET_SWAP,
};

static struct page *mc_handle_present_pte(struct vm_area_struct *vma,
                                                unsigned long addr, pte_t ptent)
{
        struct page *page = vm_normal_page(vma, addr, ptent);

        if (!page || !page_mapped(page))
                return NULL;
        if (PageAnon(page)) {
                if (!(mc.flags & MOVE_ANON))
                        return NULL;
        } else {
                if (!(mc.flags & MOVE_FILE))
                        return NULL;
        }
        if (!get_page_unless_zero(page))
                return NULL;

        return page;
}

#ifdef CONFIG_SWAP
static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        struct page *page = NULL;
        swp_entry_t ent = pte_to_swp_entry(ptent);

        if (!(mc.flags & MOVE_ANON) || non_swap_entry(ent))
                return NULL;
        /*
         * Because lookup_swap_cache() updates some statistics counter,
         * we call find_get_page() with swapper_space directly.
         */
        page = find_get_page(swap_address_space(ent), ent.val);
        if (do_swap_account)
                entry->val = ent.val;

        return page;
}
#else
static struct page *mc_handle_swap_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        return NULL;
}
#endif

static struct page *mc_handle_file_pte(struct vm_area_struct *vma,
                        unsigned long addr, pte_t ptent, swp_entry_t *entry)
{
        struct page *page = NULL;
        struct address_space *mapping;
        pgoff_t pgoff;

        if (!vma->vm_file) /* anonymous vma */
                return NULL;
        if (!(mc.flags & MOVE_FILE))
                return NULL;

        mapping = vma->vm_file->f_mapping;
        pgoff = linear_page_index(vma, addr);

        /* page is moved even if it's not RSS of this task(page-faulted). */
#ifdef CONFIG_SWAP
        /* shmem/tmpfs may report page out on swap: account for that too. */
        if (shmem_mapping(mapping)) {
                page = find_get_entry(mapping, pgoff);
                if (radix_tree_exceptional_entry(page)) {
                        swp_entry_t swp = radix_to_swp_entry(page);
                        if (do_swap_account)
                                *entry = swp;
                        page = find_get_page(swap_address_space(swp), swp.val);
                }
        } else
                page = find_get_page(mapping, pgoff);
#else
        page = find_get_page(mapping, pgoff);
#endif
        return page;
}

static enum mc_target_type get_mctgt_type(struct vm_area_struct *vma,
                unsigned long addr, pte_t ptent, union mc_target *target)
{
        struct page *page = NULL;
        enum mc_target_type ret = MC_TARGET_NONE;
        swp_entry_t ent = { .val = 0 };

        if (pte_present(ptent))
                page = mc_handle_present_pte(vma, addr, ptent);
        else if (is_swap_pte(ptent))
                page = mc_handle_swap_pte(vma, addr, ptent, &ent);
        else if (pte_none(ptent))
                page = mc_handle_file_pte(vma, addr, ptent, &ent);

        if (!page && !ent.val)
                return ret;
        if (page) {
                /*
                 * Do only loose check w/o serialization.
                 * mem_cgroup_move_account() checks the page is valid or
                 * not under LRU exclusion.
                 */
                if (page->mem_cgroup == mc.from) {
                        ret = MC_TARGET_PAGE;
                        if (target)
                                target->page = page;
                }
                if (!ret || !target)
                        put_page(page);
        }
        /* There is a swap entry and a page doesn't exist or isn't charged */
        if (ent.val && !ret &&
            mem_cgroup_id(mc.from) == lookup_swap_cgroup_id(ent)) {
                ret = MC_TARGET_SWAP;
                if (target)
                        target->ent = ent;
        }
        return ret;
}

#ifdef CONFIG_TRANSPARENT_HUGEPAGE
/*
 * We don't consider swapping or file mapped pages because THP does not
 * support them for now.
 * Caller should make sure that pmd_trans_huge(pmd) is true.
 */
static enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
                unsigned long addr, pmd_t pmd, union mc_target *target)
{
        struct page *page = NULL;
        enum mc_target_type ret = MC_TARGET_NONE;

        page = pmd_page(pmd);
        VM_BUG_ON_PAGE(!page || !PageHead(page), page);
        if (!(mc.flags & MOVE_ANON))
                return ret;
        if (page->mem_cgroup == mc.from) {
                ret = MC_TARGET_PAGE;
                if (target) {
                        get_page(page);
                        target->page = page;
                }
        }
        return ret;
}
#else
static inline enum mc_target_type get_mctgt_type_thp(struct vm_area_struct *vma,
                unsigned long addr, pmd_t pmd, union mc_target *target)
{
        return MC_TARGET_NONE;
}
#endif

static int mem_cgroup_count_precharge_pte_range(pmd_t *pmd,
                                        unsigned long addr, unsigned long end,
                                        struct mm_walk *walk)
{
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;

        if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
                if (get_mctgt_type_thp(vma, addr, *pmd, NULL) == MC_TARGET_PAGE)
                        mc.precharge += HPAGE_PMD_NR;
                spin_unlock(ptl);
                return 0;
        }

        if (pmd_trans_unstable(pmd))
                return 0;
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; pte++, addr += PAGE_SIZE)
                if (get_mctgt_type(vma, addr, *pte, NULL))
                        mc.precharge++; /* increment precharge temporarily */
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        return 0;
}

static unsigned long mem_cgroup_count_precharge(struct mm_struct *mm)
{
        unsigned long precharge;
        struct vm_area_struct *vma;

        down_read(&mm->mmap_sem);
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                struct mm_walk mem_cgroup_count_precharge_walk = {
                        .pmd_entry = mem_cgroup_count_precharge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                walk_page_range(vma->vm_start, vma->vm_end,
                                        &mem_cgroup_count_precharge_walk);
        }
        up_read(&mm->mmap_sem);

        precharge = mc.precharge;
        mc.precharge = 0;

        return precharge;
}

static int mem_cgroup_precharge_mc(struct mm_struct *mm)
{
        unsigned long precharge = mem_cgroup_count_precharge(mm);

        VM_BUG_ON(mc.moving_task);
        mc.moving_task = current;
        return mem_cgroup_do_precharge(precharge);
}

/* cancels all extra charges on mc.from and mc.to, and wakes up all waiters. */
static void __mem_cgroup_clear_mc(void)
{
        struct mem_cgroup *from = mc.from;
        struct mem_cgroup *to = mc.to;

        /* we must uncharge all the leftover precharges from mc.to */
        if (mc.precharge) {
                cancel_charge(mc.to, mc.precharge);
                mc.precharge = 0;
        }
        /*
         * we didn't uncharge from mc.from at mem_cgroup_move_account(), so
         * we must uncharge here.
         */
        if (mc.moved_charge) {
                cancel_charge(mc.from, mc.moved_charge);
                mc.moved_charge = 0;
        }
        /* we must fixup refcnts and charges */
        if (mc.moved_swap) {
                /* uncharge swap account from the old cgroup */
                if (!mem_cgroup_is_root(mc.from))
                        page_counter_uncharge(&mc.from->memsw, mc.moved_swap);

                /*
                 * we charged both to->memory and to->memsw, so we
                 * should uncharge to->memory.
                 */
                if (!mem_cgroup_is_root(mc.to))
                        page_counter_uncharge(&mc.to->memory, mc.moved_swap);

                css_put_many(&mc.from->css, mc.moved_swap);

                /* we've already done css_get(mc.to) */
                mc.moved_swap = 0;
        }
        memcg_oom_recover(from);
        memcg_oom_recover(to);
        wake_up_all(&mc.waitq);
}

static void mem_cgroup_clear_mc(void)
{
        /*
         * we must clear moving_task before waking up waiters at the end of
         * task migration.
         */
        mc.moving_task = NULL;
        __mem_cgroup_clear_mc();
        spin_lock(&mc.lock);
        mc.from = NULL;
        mc.to = NULL;
        spin_unlock(&mc.lock);
}

static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        struct task_struct *p = cgroup_taskset_first(tset);
        int ret = 0;
        struct mem_cgroup *memcg = mem_cgroup_from_css(css);
        unsigned long move_flags;

        /*
         * We are now commited to this value whatever it is. Changes in this
         * tunable will only affect upcoming migrations, not the current one.
         * So we need to save it, and keep it going.
         */
        move_flags = ACCESS_ONCE(memcg->move_charge_at_immigrate);
        if (move_flags) {
                struct mm_struct *mm;
                struct mem_cgroup *from = mem_cgroup_from_task(p);

                VM_BUG_ON(from == memcg);

                mm = get_task_mm(p);
                if (!mm)
                        return 0;
                /* We move charges only when we move a owner of the mm */
                if (mm->owner == p) {
                        VM_BUG_ON(mc.from);
                        VM_BUG_ON(mc.to);
                        VM_BUG_ON(mc.precharge);
                        VM_BUG_ON(mc.moved_charge);
                        VM_BUG_ON(mc.moved_swap);

                        spin_lock(&mc.lock);
                        mc.from = from;
                        mc.to = memcg;
                        mc.flags = move_flags;
                        spin_unlock(&mc.lock);
                        /* We set mc.moving_task later */

                        ret = mem_cgroup_precharge_mc(mm);
                        if (ret)
                                mem_cgroup_clear_mc();
                }
                mmput(mm);
        }
        return ret;
}

static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
                                     struct cgroup_taskset *tset)
{
        if (mc.to)
                mem_cgroup_clear_mc();
}

static int mem_cgroup_move_charge_pte_range(pmd_t *pmd,
                                unsigned long addr, unsigned long end,
                                struct mm_walk *walk)
{
        int ret = 0;
        struct vm_area_struct *vma = walk->private;
        pte_t *pte;
        spinlock_t *ptl;
        enum mc_target_type target_type;
        union mc_target target;
        struct page *page;

        /*
         * We don't take compound_lock() here but no race with splitting thp
         * happens because:
         *  - if pmd_trans_huge_lock() returns 1, the relevant thp is not
         *    under splitting, which means there's no concurrent thp split,
         *  - if another thread runs into split_huge_page() just after we
         *    entered this if-block, the thread must wait for page table lock
         *    to be unlocked in __split_huge_page_splitting(), where the main
         *    part of thp split is not executed yet.
         */
        if (pmd_trans_huge_lock(pmd, vma, &ptl) == 1) {
                if (mc.precharge < HPAGE_PMD_NR) {
                        spin_unlock(ptl);
                        return 0;
                }
                target_type = get_mctgt_type_thp(vma, addr, *pmd, &target);
                if (target_type == MC_TARGET_PAGE) {
                        page = target.page;
                        if (!isolate_lru_page(page)) {
                                if (!mem_cgroup_move_account(page, HPAGE_PMD_NR,
                                                             mc.from, mc.to)) {
                                        mc.precharge -= HPAGE_PMD_NR;
                                        mc.moved_charge += HPAGE_PMD_NR;
                                }
                                putback_lru_page(page);
                        }
                        put_page(page);
                }
                spin_unlock(ptl);
                return 0;
        }

        if (pmd_trans_unstable(pmd))
                return 0;
retry:
        pte = pte_offset_map_lock(vma->vm_mm, pmd, addr, &ptl);
        for (; addr != end; addr += PAGE_SIZE) {
                pte_t ptent = *(pte++);
                swp_entry_t ent;

                if (!mc.precharge)
                        break;

                switch (get_mctgt_type(vma, addr, ptent, &target)) {
                case MC_TARGET_PAGE:
                        page = target.page;
                        if (isolate_lru_page(page))
                                goto put;
                        if (!mem_cgroup_move_account(page, 1, mc.from, mc.to)) {
                                mc.precharge--;
                                /* we uncharge from mc.from later. */
                                mc.moved_charge++;
                        }
                        putback_lru_page(page);
put:                    /* get_mctgt_type() gets the page */
                        put_page(page);
                        break;
                case MC_TARGET_SWAP:
                        ent = target.ent;
                        if (!mem_cgroup_move_swap_account(ent, mc.from, mc.to)) {
                                mc.precharge--;
                                /* we fixup refcnts and charges later. */
                                mc.moved_swap++;
                        }
                        break;
                default:
                        break;
                }
        }
        pte_unmap_unlock(pte - 1, ptl);
        cond_resched();

        if (addr != end) {
                /*
                 * We have consumed all precharges we got in can_attach().
                 * We try charge one by one, but don't do any additional
                 * charges to mc.to if we have failed in charge once in attach()
                 * phase.
                 */
                ret = mem_cgroup_do_precharge(1);
                if (!ret)
                        goto retry;
        }

        return ret;
}

static void mem_cgroup_move_charge(struct mm_struct *mm)
{
        struct vm_area_struct *vma;

        lru_add_drain_all();
        /*
         * Signal mem_cgroup_begin_page_stat() to take the memcg's
         * move_lock while we're moving its pages to another memcg.
         * Then wait for already started RCU-only updates to finish.
         */
        atomic_inc(&mc.from->moving_account);
        synchronize_rcu();
retry:
        if (unlikely(!down_read_trylock(&mm->mmap_sem))) {
                /*
                 * Someone who are holding the mmap_sem might be waiting in
                 * waitq. So we cancel all extra charges, wake up all waiters,
                 * and retry. Because we cancel precharges, we might not be able
                 * to move enough charges, but moving charge is a best-effort
                 * feature anyway, so it wouldn't be a big problem.
                 */
                __mem_cgroup_clear_mc();
                cond_resched();
                goto retry;
        }
        for (vma = mm->mmap; vma; vma = vma->vm_next) {
                int ret;
                struct mm_walk mem_cgroup_move_charge_walk = {
                        .pmd_entry = mem_cgroup_move_charge_pte_range,
                        .mm = mm,
                        .private = vma,
                };
                if (is_vm_hugetlb_page(vma))
                        continue;
                ret = walk_page_range(vma->vm_start, vma->vm_end,
                                                &mem_cgroup_move_charge_walk);
                if (ret)
                        /*
                         * means we have consumed all precharges and failed in
                         * doing additional charge. Just abandon here.
                         */
                        break;
        }
        up_read(&mm->mmap_sem);
        atomic_dec(&mc.from->moving_account);
}

static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        struct task_struct *p = cgroup_taskset_first(tset);
        struct mm_struct *mm = get_task_mm(p);

        if (mm) {
                if (mc.to)
                        mem_cgroup_move_charge(mm);
                mmput(mm);
        }
        if (mc.to)
                mem_cgroup_clear_mc();
}
#else   /* !CONFIG_MMU */
static int mem_cgroup_can_attach(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
        return 0;
}
static void mem_cgroup_cancel_attach(struct cgroup_subsys_state *css,
                                     struct cgroup_taskset *tset)
{
}
static void mem_cgroup_move_task(struct cgroup_subsys_state *css,
                                 struct cgroup_taskset *tset)
{
}
#endif

/*
 * Cgroup retains root cgroups across [un]mount cycles making it necessary
 * to verify whether we're attached to the default hierarchy on each mount
 * attempt.
 */
static void mem_cgroup_bind(struct cgroup_subsys_state *root_css)
{
        /*
         * use_hierarchy is forced on the default hierarchy.  cgroup core
         * guarantees that @root doesn't have any children, so turning it
         * on for the root memcg is enough.
         */
        if (cgroup_on_dfl(root_css->cgroup))
                mem_cgroup_from_css(root_css)->use_hierarchy = true;
}

static u64 memory_current_read(struct cgroup_subsys_state *css,
                               struct cftype *cft)
{
        return mem_cgroup_usage(mem_cgroup_from_css(css), false);
}

static int memory_low_show(struct seq_file *m, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
        unsigned long low = ACCESS_ONCE(memcg->low);

        if (low == PAGE_COUNTER_MAX)
                seq_puts(m, "infinity\n");
        else
                seq_printf(m, "%llu\n", (u64)low * PAGE_SIZE);

        return 0;
}

static ssize_t memory_low_write(struct kernfs_open_file *of,
                                char *buf, size_t nbytes, loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
        unsigned long low;
        int err;

        buf = strstrip(buf);
        err = page_counter_memparse(buf, "infinity", &low);
        if (err)
                return err;

        memcg->low = low;

        return nbytes;
}

static int memory_high_show(struct seq_file *m, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
        unsigned long high = ACCESS_ONCE(memcg->high);

        if (high == PAGE_COUNTER_MAX)
                seq_puts(m, "infinity\n");
        else
                seq_printf(m, "%llu\n", (u64)high * PAGE_SIZE);

        return 0;
}

static ssize_t memory_high_write(struct kernfs_open_file *of,
                                 char *buf, size_t nbytes, loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
        unsigned long high;
        int err;

        buf = strstrip(buf);
        err = page_counter_memparse(buf, "infinity", &high);
        if (err)
                return err;

        memcg->high = high;

        return nbytes;
}

static int memory_max_show(struct seq_file *m, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));
        unsigned long max = ACCESS_ONCE(memcg->memory.limit);

        if (max == PAGE_COUNTER_MAX)
                seq_puts(m, "infinity\n");
        else
                seq_printf(m, "%llu\n", (u64)max * PAGE_SIZE);

        return 0;
}

static ssize_t memory_max_write(struct kernfs_open_file *of,
                                char *buf, size_t nbytes, loff_t off)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(of_css(of));
        unsigned long max;
        int err;

        buf = strstrip(buf);
        err = page_counter_memparse(buf, "infinity", &max);
        if (err)
                return err;

        err = mem_cgroup_resize_limit(memcg, max);
        if (err)
                return err;

        return nbytes;
}

static int memory_events_show(struct seq_file *m, void *v)
{
        struct mem_cgroup *memcg = mem_cgroup_from_css(seq_css(m));

        seq_printf(m, "low %lu\n", mem_cgroup_read_events(memcg, MEMCG_LOW));
        seq_printf(m, "high %lu\n", mem_cgroup_read_events(memcg, MEMCG_HIGH));
        seq_printf(m, "max %lu\n", mem_cgroup_read_events(memcg, MEMCG_MAX));
        seq_printf(m, "oom %lu\n", mem_cgroup_read_events(memcg, MEMCG_OOM));

        return 0;
}

static struct cftype memory_files[] = {
        {
                .name = "current",
                .read_u64 = memory_current_read,
        },
        {
                .name = "low",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = memory_low_show,
                .write = memory_low_write,
        },
        {
                .name = "high",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = memory_high_show,
                .write = memory_high_write,
        },
        {
                .name = "max",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = memory_max_show,
                .write = memory_max_write,
        },
        {
                .name = "events",
                .flags = CFTYPE_NOT_ON_ROOT,
                .seq_show = memory_events_show,
        },
        { }     /* terminate */
};

struct cgroup_subsys memory_cgrp_subsys = {
        .css_alloc = mem_cgroup_css_alloc,
        .css_online = mem_cgroup_css_online,
        .css_offline = mem_cgroup_css_offline,
        .css_free = mem_cgroup_css_free,
        .css_reset = mem_cgroup_css_reset,
        .can_attach = mem_cgroup_can_attach,
        .cancel_attach = mem_cgroup_cancel_attach,
        .attach = mem_cgroup_move_task,
        .bind = mem_cgroup_bind,
        .dfl_cftypes = memory_files,
        .legacy_cftypes = mem_cgroup_legacy_files,
        .early_init = 0,
};

#ifdef CONFIG_MEMCG_SWAP
static int __init enable_swap_account(char *s)
{
        if (!strcmp(s, "1"))
                really_do_swap_account = 1;
        else if (!strcmp(s, "0"))
                really_do_swap_account = 0;
        return 1;
}
__setup("swapaccount=", enable_swap_account);

static void __init memsw_file_init(void)
{
        WARN_ON(cgroup_add_legacy_cftypes(&memory_cgrp_subsys,
                                          memsw_cgroup_files));
}

static void __init enable_swap_cgroup(void)
{
        if (!mem_cgroup_disabled() && really_do_swap_account) {
                do_swap_account = 1;
                memsw_file_init();
        }
}

#else
static void __init enable_swap_cgroup(void)
{
}
#endif

/**
 * mem_cgroup_events - count memory events against a cgroup
 * @memcg: the memory cgroup
 * @idx: the event index
 * @nr: the number of events to account for
 */
void mem_cgroup_events(struct mem_cgroup *memcg,
                       enum mem_cgroup_events_index idx,
                       unsigned int nr)
{
        this_cpu_add(memcg->stat->events[idx], nr);
}

/**
 * mem_cgroup_low - check if memory consumption is below the normal range
 * @root: the highest ancestor to consider
 * @memcg: the memory cgroup to check
 *
 * Returns %true if memory consumption of @memcg, and that of all
 * configurable ancestors up to @root, is below the normal range.
 */
bool mem_cgroup_low(struct mem_cgroup *root, struct mem_cgroup *memcg)
{
        if (mem_cgroup_disabled())
                return false;

        /*
         * The toplevel group doesn't have a configurable range, so
         * it's never low when looked at directly, and it is not
         * considered an ancestor when assessing the hierarchy.
         */

        if (memcg == root_mem_cgroup)
                return false;

        if (page_counter_read(&memcg->memory) > memcg->low)
                return false;

        while (memcg != root) {
                memcg = parent_mem_cgroup(memcg);

                if (memcg == root_mem_cgroup)
                        break;

                if (page_counter_read(&memcg->memory) > memcg->low)
                        return false;
        }
        return true;
}

#ifdef CONFIG_MEMCG_SWAP
/**
 * mem_cgroup_swapout - transfer a memsw charge to swap
 * @page: page whose memsw charge to transfer
 * @entry: swap entry to move the charge to
 *
 * Transfer the memsw charge of @page to @entry.
 */
void mem_cgroup_swapout(struct page *page, swp_entry_t entry)
{
        struct mem_cgroup *memcg;
        unsigned short oldid;

        VM_BUG_ON_PAGE(PageLRU(page), page);
        VM_BUG_ON_PAGE(page_count(page), page);

        if (!do_swap_account)
                return;

        memcg = page->mem_cgroup;

        /* Readahead page, never charged */
        if (!memcg)
                return;

        oldid = swap_cgroup_record(entry, mem_cgroup_id(memcg));
        VM_BUG_ON_PAGE(oldid, page);
        mem_cgroup_swap_statistics(memcg, true);

        page->mem_cgroup = NULL;

        if (!mem_cgroup_is_root(memcg))
                page_counter_uncharge(&memcg->memory, 1);

        /* XXX: caller holds IRQ-safe mapping->tree_lock */
        VM_BUG_ON(!irqs_disabled());

        mem_cgroup_charge_statistics(memcg, page, -1);
        memcg_check_events(memcg, page);
}

/**
 * mem_cgroup_uncharge_swap - uncharge a swap entry
 * @entry: swap entry to uncharge
 *
 * Drop the memsw charge associated with @entry.
 */
void mem_cgroup_uncharge_swap(swp_entry_t entry)
{
        struct mem_cgroup *memcg;
        unsigned short id;

        if (!do_swap_account)
                return;

        id = swap_cgroup_record(entry, 0);
        rcu_read_lock();
        memcg = mem_cgroup_lookup(id);
        if (memcg) {
                if (!mem_cgroup_is_root(memcg))
                        page_counter_uncharge(&memcg->memsw, 1);
                mem_cgroup_swap_statistics(memcg, false);
                css_put(&memcg->css);
        }
        rcu_read_unlock();
}
#endif

/**
 * mem_cgroup_try_charge - try charging a page
 * @page: page to charge
 * @mm: mm context of the victim
 * @gfp_mask: reclaim mode
 * @memcgp: charged memcg return
 *
 * Try to charge @page to the memcg that @mm belongs to, reclaiming
 * pages according to @gfp_mask if necessary.
 *
 * Returns 0 on success, with *@memcgp pointing to the charged memcg.
 * Otherwise, an error code is returned.
 *
 * After page->mapping has been set up, the caller must finalize the
 * charge with mem_cgroup_commit_charge().  Or abort the transaction
 * with mem_cgroup_cancel_charge() in case page instantiation fails.
 */
int mem_cgroup_try_charge(struct page *page, struct mm_struct *mm,
                          gfp_t gfp_mask, struct mem_cgroup **memcgp)
{
        struct mem_cgroup *memcg = NULL;
        unsigned int nr_pages = 1;
        int ret = 0;

        if (mem_cgroup_disabled())
                goto out;

        if (PageSwapCache(page)) {
                /*
                 * Every swap fault against a single page tries to charge the
                 * page, bail as early as possible.  shmem_unuse() encounters
                 * already charged pages, too.  The USED bit is protected by
                 * the page lock, which serializes swap cache removal, which
                 * in turn serializes uncharging.
                 */
                if (page->mem_cgroup)
                        goto out;
        }

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON_PAGE(!PageTransHuge(page), page);
        }

        if (do_swap_account && PageSwapCache(page))
                memcg = try_get_mem_cgroup_from_page(page);
        if (!memcg)
                memcg = get_mem_cgroup_from_mm(mm);

        ret = try_charge(memcg, gfp_mask, nr_pages);

        css_put(&memcg->css);

        if (ret == -EINTR) {
                memcg = root_mem_cgroup;
                ret = 0;
        }
out:
        *memcgp = memcg;
        return ret;
}

/**
 * mem_cgroup_commit_charge - commit a page charge
 * @page: page to charge
 * @memcg: memcg to charge the page to
 * @lrucare: page might be on LRU already
 *
 * Finalize a charge transaction started by mem_cgroup_try_charge(),
 * after page->mapping has been set up.  This must happen atomically
 * as part of the page instantiation, i.e. under the page table lock
 * for anonymous pages, under the page lock for page and swap cache.
 *
 * In addition, the page must not be on the LRU during the commit, to
 * prevent racing with task migration.  If it might be, use @lrucare.
 *
 * Use mem_cgroup_cancel_charge() to cancel the transaction instead.
 */
void mem_cgroup_commit_charge(struct page *page, struct mem_cgroup *memcg,
                              bool lrucare)
{
        unsigned int nr_pages = 1;

        VM_BUG_ON_PAGE(!page->mapping, page);
        VM_BUG_ON_PAGE(PageLRU(page) && !lrucare, page);

        if (mem_cgroup_disabled())
                return;
        /*
         * Swap faults will attempt to charge the same page multiple
         * times.  But reuse_swap_page() might have removed the page
         * from swapcache already, so we can't check PageSwapCache().
         */
        if (!memcg)
                return;

        commit_charge(page, memcg, lrucare);

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON_PAGE(!PageTransHuge(page), page);
        }

        local_irq_disable();
        mem_cgroup_charge_statistics(memcg, page, nr_pages);
        memcg_check_events(memcg, page);
        local_irq_enable();

        if (do_swap_account && PageSwapCache(page)) {
                swp_entry_t entry = { .val = page_private(page) };
                /*
                 * The swap entry might not get freed for a long time,
                 * let's not wait for it.  The page already received a
                 * memory+swap charge, drop the swap entry duplicate.
                 */
                mem_cgroup_uncharge_swap(entry);
        }
}

/**
 * mem_cgroup_cancel_charge - cancel a page charge
 * @page: page to charge
 * @memcg: memcg to charge the page to
 *
 * Cancel a charge transaction started by mem_cgroup_try_charge().
 */
void mem_cgroup_cancel_charge(struct page *page, struct mem_cgroup *memcg)
{
        unsigned int nr_pages = 1;

        if (mem_cgroup_disabled())
                return;
        /*
         * Swap faults will attempt to charge the same page multiple
         * times.  But reuse_swap_page() might have removed the page
         * from swapcache already, so we can't check PageSwapCache().
         */
        if (!memcg)
                return;

        if (PageTransHuge(page)) {
                nr_pages <<= compound_order(page);
                VM_BUG_ON_PAGE(!PageTransHuge(page), page);
        }

        cancel_charge(memcg, nr_pages);
}

static void uncharge_batch(struct mem_cgroup *memcg, unsigned long pgpgout,
                           unsigned long nr_anon, unsigned long nr_file,
                           unsigned long nr_huge, struct page *dummy_page)
{
        unsigned long nr_pages = nr_anon + nr_file;
        unsigned long flags;

        if (!mem_cgroup_is_root(memcg)) {
                page_counter_uncharge(&memcg->memory, nr_pages);
                if (do_swap_account)
                        page_counter_uncharge(&memcg->memsw, nr_pages);
                memcg_oom_recover(memcg);
        }

        local_irq_save(flags);
        __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS], nr_anon);
        __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_CACHE], nr_file);
        __this_cpu_sub(memcg->stat->count[MEM_CGROUP_STAT_RSS_HUGE], nr_huge);
        __this_cpu_add(memcg->stat->events[MEM_CGROUP_EVENTS_PGPGOUT], pgpgout);
        __this_cpu_add(memcg->stat->nr_page_events, nr_pages);
        memcg_check_events(memcg, dummy_page);
        local_irq_restore(flags);

        if (!mem_cgroup_is_root(memcg))
                css_put_many(&memcg->css, nr_pages);
}

static void uncharge_list(struct list_head *page_list)
{
        struct mem_cgroup *memcg = NULL;
        unsigned long nr_anon = 0;
        unsigned long nr_file = 0;
        unsigned long nr_huge = 0;
        unsigned long pgpgout = 0;
        struct list_head *next;
        struct page *page;

        next = page_list->next;
        do {
                unsigned int nr_pages = 1;

                page = list_entry(next, struct page, lru);
                next = page->lru.next;

                VM_BUG_ON_PAGE(PageLRU(page), page);
                VM_BUG_ON_PAGE(page_count(page), page);

                if (!page->mem_cgroup)
                        continue;

                /*
                 * Nobody should be changing or seriously looking at
                 * page->mem_cgroup at this point, we have fully
                 * exclusive access to the page.
                 */

                if (memcg != page->mem_cgroup) {
                        if (memcg) {
                                uncharge_batch(memcg, pgpgout, nr_anon, nr_file,
                                               nr_huge, page);
                                pgpgout = nr_anon = nr_file = nr_huge = 0;
                        }
                        memcg = page->mem_cgroup;
                }

                if (PageTransHuge(page)) {
                        nr_pages <<= compound_order(page);
                        VM_BUG_ON_PAGE(!PageTransHuge(page), page);
                        nr_huge += nr_pages;
                }

                if (PageAnon(page))
                        nr_anon += nr_pages;
                else
                        nr_file += nr_pages;

                page->mem_cgroup = NULL;

                pgpgout++;
        } while (next != page_list);

        if (memcg)
                uncharge_batch(memcg, pgpgout, nr_anon, nr_file,
                               nr_huge, page);
}

/**
 * mem_cgroup_uncharge - uncharge a page
 * @page: page to uncharge
 *
 * Uncharge a page previously charged with mem_cgroup_try_charge() and
 * mem_cgroup_commit_charge().
 */
void mem_cgroup_uncharge(struct page *page)
{
        if (mem_cgroup_disabled())
                return;

        /* Don't touch page->lru of any random page, pre-check: */
        if (!page->mem_cgroup)
                return;

        INIT_LIST_HEAD(&page->lru);
        uncharge_list(&page->lru);
}

/**
 * mem_cgroup_uncharge_list - uncharge a list of page
 * @page_list: list of pages to uncharge
 *
 * Uncharge a list of pages previously charged with
 * mem_cgroup_try_charge() and mem_cgroup_commit_charge().
 */
void mem_cgroup_uncharge_list(struct list_head *page_list)
{
        if (mem_cgroup_disabled())
                return;

        if (!list_empty(page_list))
                uncharge_list(page_list);
}

/**
 * mem_cgroup_migrate - migrate a charge to another page
 * @oldpage: currently charged page
 * @newpage: page to transfer the charge to
 * @lrucare: either or both pages might be on the LRU already
 *
 * Migrate the charge from @oldpage to @newpage.
 *
 * Both pages must be locked, @newpage->mapping must be set up.
 */
void mem_cgroup_migrate(struct page *oldpage, struct page *newpage,
                        bool lrucare)
{
        struct mem_cgroup *memcg;
        int isolated;

        VM_BUG_ON_PAGE(!PageLocked(oldpage), oldpage);
        VM_BUG_ON_PAGE(!PageLocked(newpage), newpage);
        VM_BUG_ON_PAGE(!lrucare && PageLRU(oldpage), oldpage);
        VM_BUG_ON_PAGE(!lrucare && PageLRU(newpage), newpage);
        VM_BUG_ON_PAGE(PageAnon(oldpage) != PageAnon(newpage), newpage);
        VM_BUG_ON_PAGE(PageTransHuge(oldpage) != PageTransHuge(newpage),
                       newpage);

        if (mem_cgroup_disabled())
                return;

        /* Page cache replacement: new page already charged? */
        if (newpage->mem_cgroup)
                return;

        /*
         * Swapcache readahead pages can get migrated before being
         * charged, and migration from compaction can happen to an
         * uncharged page when the PFN walker finds a page that
         * reclaim just put back on the LRU but has not released yet.
         */
        memcg = oldpage->mem_cgroup;
        if (!memcg)
                return;

        if (lrucare)
                lock_page_lru(oldpage, &isolated);

        oldpage->mem_cgroup = NULL;

        if (lrucare)
                unlock_page_lru(oldpage, isolated);

        commit_charge(newpage, memcg, lrucare);
}

/*
 * subsys_initcall() for memory controller.
 *
 * Some parts like hotcpu_notifier() have to be initialized from this context
 * because of lock dependencies (cgroup_lock -> cpu hotplug) but basically
 * everything that doesn't depend on a specific mem_cgroup structure should
 * be initialized from here.
 */
static int __init mem_cgroup_init(void)
{
        hotcpu_notifier(memcg_cpu_hotplug_callback, 0);
        enable_swap_cgroup();
        mem_cgroup_soft_limit_tree_init();
        memcg_stock_init();
        return 0;
}
subsys_initcall(mem_cgroup_init);