--- /dev/null
+/*
+ * Percpu IDA library
+ *
+ * Copyright (C) 2013 Datera, Inc. Kent Overstreet
+ *
+ * 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, 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/bitmap.h>
+#include <linux/bitops.h>
+#include <linux/bug.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/hardirq.h>
+#include <linux/idr.h>
+#include <linux/init.h>
+#include <linux/kernel.h>
+#include <linux/percpu.h>
+#include <linux/sched.h>
+#include <linux/slab.h>
+#include <linux/string.h>
+#include <linux/spinlock.h>
+#include <linux/percpu_ida.h>
+
+/*
+ * Number of tags we move between the percpu freelist and the global freelist at
+ * a time
+ */
+#define IDA_PCPU_BATCH_MOVE 32U
+
+/* Max size of percpu freelist, */
+#define IDA_PCPU_SIZE ((IDA_PCPU_BATCH_MOVE * 3) / 2)
+
+struct percpu_ida_cpu {
+ /*
+ * Even though this is percpu, we need a lock for tag stealing by remote
+ * CPUs:
+ */
+ spinlock_t lock;
+
+ /* nr_free/freelist form a stack of free IDs */
+ unsigned nr_free;
+ unsigned freelist[];
+};
+
+static inline void move_tags(unsigned *dst, unsigned *dst_nr,
+ unsigned *src, unsigned *src_nr,
+ unsigned nr)
+{
+ *src_nr -= nr;
+ memcpy(dst + *dst_nr, src + *src_nr, sizeof(unsigned) * nr);
+ *dst_nr += nr;
+}
+
+/*
+ * Try to steal tags from a remote cpu's percpu freelist.
+ *
+ * We first check how many percpu freelists have tags - we don't steal tags
+ * unless enough percpu freelists have tags on them that it's possible more than
+ * half the total tags could be stuck on remote percpu freelists.
+ *
+ * Then we iterate through the cpus until we find some tags - we don't attempt
+ * to find the "best" cpu to steal from, to keep cacheline bouncing to a
+ * minimum.
+ */
+static inline void steal_tags(struct percpu_ida *pool,
+ struct percpu_ida_cpu *tags)
+{
+ unsigned cpus_have_tags, cpu = pool->cpu_last_stolen;
+ struct percpu_ida_cpu *remote;
+
+ for (cpus_have_tags = cpumask_weight(&pool->cpus_have_tags);
+ cpus_have_tags * IDA_PCPU_SIZE > pool->nr_tags / 2;
+ cpus_have_tags--) {
+ cpu = cpumask_next(cpu, &pool->cpus_have_tags);
+
+ if (cpu >= nr_cpu_ids) {
+ cpu = cpumask_first(&pool->cpus_have_tags);
+ if (cpu >= nr_cpu_ids)
+ BUG();
+ }
+
+ pool->cpu_last_stolen = cpu;
+ remote = per_cpu_ptr(pool->tag_cpu, cpu);
+
+ cpumask_clear_cpu(cpu, &pool->cpus_have_tags);
+
+ if (remote == tags)
+ continue;
+
+ spin_lock(&remote->lock);
+
+ if (remote->nr_free) {
+ memcpy(tags->freelist,
+ remote->freelist,
+ sizeof(unsigned) * remote->nr_free);
+
+ tags->nr_free = remote->nr_free;
+ remote->nr_free = 0;
+ }
+
+ spin_unlock(&remote->lock);
+
+ if (tags->nr_free)
+ break;
+ }
+}
+
+/*
+ * Pop up to IDA_PCPU_BATCH_MOVE IDs off the global freelist, and push them onto
+ * our percpu freelist:
+ */
+static inline void alloc_global_tags(struct percpu_ida *pool,
+ struct percpu_ida_cpu *tags)
+{
+ move_tags(tags->freelist, &tags->nr_free,
+ pool->freelist, &pool->nr_free,
+ min(pool->nr_free, IDA_PCPU_BATCH_MOVE));
+}
+
+static inline unsigned alloc_local_tag(struct percpu_ida *pool,
+ struct percpu_ida_cpu *tags)
+{
+ int tag = -ENOSPC;
+
+ spin_lock(&tags->lock);
+ if (tags->nr_free)
+ tag = tags->freelist[--tags->nr_free];
+ spin_unlock(&tags->lock);
+
+ return tag;
+}
+
+/**
+ * percpu_ida_alloc - allocate a tag
+ * @pool: pool to allocate from
+ * @gfp: gfp flags
+ *
+ * Returns a tag - an integer in the range [0..nr_tags) (passed to
+ * tag_pool_init()), or otherwise -ENOSPC on allocation failure.
+ *
+ * Safe to be called from interrupt context (assuming it isn't passed
+ * __GFP_WAIT, of course).
+ *
+ * @gfp indicates whether or not to wait until a free id is available (it's not
+ * used for internal memory allocations); thus if passed __GFP_WAIT we may sleep
+ * however long it takes until another thread frees an id (same semantics as a
+ * mempool).
+ *
+ * Will not fail if passed __GFP_WAIT.
+ */
+int percpu_ida_alloc(struct percpu_ida *pool, gfp_t gfp)
+{
+ DEFINE_WAIT(wait);
+ struct percpu_ida_cpu *tags;
+ unsigned long flags;
+ int tag;
+
+ local_irq_save(flags);
+ tags = this_cpu_ptr(pool->tag_cpu);
+
+ /* Fastpath */
+ tag = alloc_local_tag(pool, tags);
+ if (likely(tag >= 0)) {
+ local_irq_restore(flags);
+ return tag;
+ }
+
+ while (1) {
+ spin_lock(&pool->lock);
+
+ /*
+ * prepare_to_wait() must come before steal_tags(), in case
+ * percpu_ida_free() on another cpu flips a bit in
+ * cpus_have_tags
+ *
+ * global lock held and irqs disabled, don't need percpu lock
+ */
+ prepare_to_wait(&pool->wait, &wait, TASK_UNINTERRUPTIBLE);
+
+ if (!tags->nr_free)
+ alloc_global_tags(pool, tags);
+ if (!tags->nr_free)
+ steal_tags(pool, tags);
+
+ if (tags->nr_free) {
+ tag = tags->freelist[--tags->nr_free];
+ if (tags->nr_free)
+ cpumask_set_cpu(smp_processor_id(),
+ &pool->cpus_have_tags);
+ }
+
+ spin_unlock(&pool->lock);
+ local_irq_restore(flags);
+
+ if (tag >= 0 || !(gfp & __GFP_WAIT))
+ break;
+
+ schedule();
+
+ local_irq_save(flags);
+ tags = this_cpu_ptr(pool->tag_cpu);
+ }
+
+ finish_wait(&pool->wait, &wait);
+ return tag;
+}
+EXPORT_SYMBOL_GPL(percpu_ida_alloc);
+
+/**
+ * percpu_ida_free - free a tag
+ * @pool: pool @tag was allocated from
+ * @tag: a tag previously allocated with percpu_ida_alloc()
+ *
+ * Safe to be called from interrupt context.
+ */
+void percpu_ida_free(struct percpu_ida *pool, unsigned tag)
+{
+ struct percpu_ida_cpu *tags;
+ unsigned long flags;
+ unsigned nr_free;
+
+ BUG_ON(tag >= pool->nr_tags);
+
+ local_irq_save(flags);
+ tags = this_cpu_ptr(pool->tag_cpu);
+
+ spin_lock(&tags->lock);
+ tags->freelist[tags->nr_free++] = tag;
+
+ nr_free = tags->nr_free;
+ spin_unlock(&tags->lock);
+
+ if (nr_free == 1) {
+ cpumask_set_cpu(smp_processor_id(),
+ &pool->cpus_have_tags);
+ wake_up(&pool->wait);
+ }
+
+ if (nr_free == IDA_PCPU_SIZE) {
+ spin_lock(&pool->lock);
+
+ /*
+ * Global lock held and irqs disabled, don't need percpu
+ * lock
+ */
+ if (tags->nr_free == IDA_PCPU_SIZE) {
+ move_tags(pool->freelist, &pool->nr_free,
+ tags->freelist, &tags->nr_free,
+ IDA_PCPU_BATCH_MOVE);
+
+ wake_up(&pool->wait);
+ }
+ spin_unlock(&pool->lock);
+ }
+
+ local_irq_restore(flags);
+}
+EXPORT_SYMBOL_GPL(percpu_ida_free);
+
+/**
+ * percpu_ida_destroy - release a tag pool's resources
+ * @pool: pool to free
+ *
+ * Frees the resources allocated by percpu_ida_init().
+ */
+void percpu_ida_destroy(struct percpu_ida *pool)
+{
+ free_percpu(pool->tag_cpu);
+ free_pages((unsigned long) pool->freelist,
+ get_order(pool->nr_tags * sizeof(unsigned)));
+}
+EXPORT_SYMBOL_GPL(percpu_ida_destroy);
+
+/**
+ * percpu_ida_init - initialize a percpu tag pool
+ * @pool: pool to initialize
+ * @nr_tags: number of tags that will be available for allocation
+ *
+ * Initializes @pool so that it can be used to allocate tags - integers in the
+ * range [0, nr_tags). Typically, they'll be used by driver code to refer to a
+ * preallocated array of tag structures.
+ *
+ * Allocation is percpu, but sharding is limited by nr_tags - for best
+ * performance, the workload should not span more cpus than nr_tags / 128.
+ */
+int percpu_ida_init(struct percpu_ida *pool, unsigned long nr_tags)
+{
+ unsigned i, cpu, order;
+
+ memset(pool, 0, sizeof(*pool));
+
+ init_waitqueue_head(&pool->wait);
+ spin_lock_init(&pool->lock);
+ pool->nr_tags = nr_tags;
+
+ /* Guard against overflow */
+ if (nr_tags > (unsigned) INT_MAX + 1) {
+ pr_err("percpu_ida_init(): nr_tags too large\n");
+ return -EINVAL;
+ }
+
+ order = get_order(nr_tags * sizeof(unsigned));
+ pool->freelist = (void *) __get_free_pages(GFP_KERNEL, order);
+ if (!pool->freelist)
+ return -ENOMEM;
+
+ for (i = 0; i < nr_tags; i++)
+ pool->freelist[i] = i;
+
+ pool->nr_free = nr_tags;
+
+ pool->tag_cpu = __alloc_percpu(sizeof(struct percpu_ida_cpu) +
+ IDA_PCPU_SIZE * sizeof(unsigned),
+ sizeof(unsigned));
+ if (!pool->tag_cpu)
+ goto err;
+
+ for_each_possible_cpu(cpu)
+ spin_lock_init(&per_cpu_ptr(pool->tag_cpu, cpu)->lock);
+
+ return 0;
+err:
+ percpu_ida_destroy(pool);
+ return -ENOMEM;
+}
+EXPORT_SYMBOL_GPL(percpu_ida_init);
projects / cascardo / linux.git / blobdiff