mm, page_alloc: remove MIGRATE_RESERVE

MIGRATE_RESERVE preserves an old property of the buddy allocator that
existed prior to fragmentation avoidance -- min_free_kbytes worth of pages
tended to remain contiguous until the only alternative was to fail the
allocation.  At the time it was discovered that high-order atomic
allocations relied on this property so MIGRATE_RESERVE was introduced.  A
later patch will introduce an alternative MIGRATE_HIGHATOMIC so this patch
deletes MIGRATE_RESERVE and supporting code so it'll be easier to review.
Note that this patch in isolation may look like a false regression if
someone was bisecting high-order atomic allocation failures.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Cc: Christoph Lameter <cl@linux.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Vitaly Wool <vitalywool@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 1e88aae..b86cfa3 100644 (file)
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -39,8 +39,6 @@ enum {
        MIGRATE_UNMOVABLE,
        MIGRATE_MOVABLE,
        MIGRATE_RECLAIMABLE,
-       MIGRATE_PCPTYPES,       /* the number of types on the pcp lists */
-       MIGRATE_RESERVE = MIGRATE_PCPTYPES,
 #ifdef CONFIG_CMA
        /*
         * MIGRATE_CMA migration type is designed to mimic the way
@@ -63,6 +61,8 @@ enum {
        MIGRATE_TYPES
 };
 
+#define MIGRATE_PCPTYPES (MIGRATE_RECLAIMABLE+1)
+
 #ifdef CONFIG_CMA
 #  define is_migrate_cma(migratetype) unlikely((migratetype) == MIGRATE_CMA)
 #else
@@ -429,12 +429,6 @@ struct zone {
 
        const char              *name;
 
-       /*
-        * Number of MIGRATE_RESERVE page block. To maintain for just
-        * optimization. Protected by zone->lock.
-        */
-       int                     nr_migrate_reserve_block;
-
 #ifdef CONFIG_MEMORY_ISOLATION
        /*
         * Number of isolated pageblock. It is used to solve incorrect

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 9812d46..dabd247 100644 (file)
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -116,7 +116,7 @@ static void set_recommended_min_free_kbytes(void)
        for_each_populated_zone(zone)
                nr_zones++;
 
-       /* Make sure at least 2 hugepages are free for MIGRATE_RESERVE */
+       /* Ensure 2 pageblocks are free to assist fragmentation avoidance */
        recommended_min = pageblock_nr_pages * nr_zones * 2;
 
        /*

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dc6e3c..5888126 100644 (file)
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -817,7 +817,6 @@ static void free_pcppages_bulk(struct zone *zone, int count,
                        if (unlikely(has_isolate_pageblock(zone)))
                                mt = get_pageblock_migratetype(page);
 
-                       /* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
                        __free_one_page(page, page_to_pfn(page), zone, 0, mt);
                        trace_mm_page_pcpu_drain(page, 0, mt);
                } while (--to_free && --batch_free && !list_empty(list));
@@ -1417,15 +1416,14 @@ struct page *__rmqueue_smallest(struct zone *zone, unsigned int order,
  * the free lists for the desirable migrate type are depleted
  */
 static int fallbacks[MIGRATE_TYPES][4] = {
-       [MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,     MIGRATE_RESERVE },
-       [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,     MIGRATE_RESERVE },
-       [MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE,   MIGRATE_RESERVE },
+       [MIGRATE_UNMOVABLE]   = { MIGRATE_RECLAIMABLE, MIGRATE_MOVABLE,   MIGRATE_TYPES },
+       [MIGRATE_RECLAIMABLE] = { MIGRATE_UNMOVABLE,   MIGRATE_MOVABLE,   MIGRATE_TYPES },
+       [MIGRATE_MOVABLE]     = { MIGRATE_RECLAIMABLE, MIGRATE_UNMOVABLE, MIGRATE_TYPES },
 #ifdef CONFIG_CMA
-       [MIGRATE_CMA]         = { MIGRATE_RESERVE }, /* Never used */
+       [MIGRATE_CMA]         = { MIGRATE_TYPES }, /* Never used */
 #endif
-       [MIGRATE_RESERVE]     = { MIGRATE_RESERVE }, /* Never used */
 #ifdef CONFIG_MEMORY_ISOLATION
-       [MIGRATE_ISOLATE]     = { MIGRATE_RESERVE }, /* Never used */
+       [MIGRATE_ISOLATE]     = { MIGRATE_TYPES }, /* Never used */
 #endif
 };
 
@@ -1598,7 +1596,7 @@ int find_suitable_fallback(struct free_area *area, unsigned int order,
        *can_steal = false;
        for (i = 0;; i++) {
                fallback_mt = fallbacks[migratetype][i];
-               if (fallback_mt == MIGRATE_RESERVE)
+               if (fallback_mt == MIGRATE_TYPES)
                        break;
 
                if (list_empty(&area->free_list[fallback_mt]))
@@ -1676,25 +1674,13 @@ static struct page *__rmqueue(struct zone *zone, unsigned int order,
 {
        struct page *page;
 
-retry_reserve:
        page = __rmqueue_smallest(zone, order, migratetype);
-
-       if (unlikely(!page) && migratetype != MIGRATE_RESERVE) {
+       if (unlikely(!page)) {
                if (migratetype == MIGRATE_MOVABLE)
                        page = __rmqueue_cma_fallback(zone, order);
 
                if (!page)
                        page = __rmqueue_fallback(zone, order, migratetype);
-
-               /*
-                * Use MIGRATE_RESERVE rather than fail an allocation. goto
-                * is used because __rmqueue_smallest is an inline function
-                * and we want just one call site
-                */
-               if (!page) {
-                       migratetype = MIGRATE_RESERVE;
-                       goto retry_reserve;
-               }
        }
 
        trace_mm_page_alloc_zone_locked(page, order, migratetype);
@@ -3492,7 +3478,6 @@ static void show_migration_types(unsigned char type)
                [MIGRATE_UNMOVABLE]     = 'U',
                [MIGRATE_RECLAIMABLE]   = 'E',
                [MIGRATE_MOVABLE]       = 'M',
-               [MIGRATE_RESERVE]       = 'R',
 #ifdef CONFIG_CMA
                [MIGRATE_CMA]           = 'C',
 #endif
@@ -4302,120 +4287,6 @@ static inline unsigned long wait_table_bits(unsigned long size)
        return ffz(~size);
 }
 
-/*
- * Check if a pageblock contains reserved pages
- */
-static int pageblock_is_reserved(unsigned long start_pfn, unsigned long end_pfn)
-{
-       unsigned long pfn;
-
-       for (pfn = start_pfn; pfn < end_pfn; pfn++) {
-               if (!pfn_valid_within(pfn) || PageReserved(pfn_to_page(pfn)))
-                       return 1;
-       }
-       return 0;
-}
-
-/*
- * Mark a number of pageblocks as MIGRATE_RESERVE. The number
- * of blocks reserved is based on min_wmark_pages(zone). The memory within
- * the reserve will tend to store contiguous free pages. Setting min_free_kbytes
- * higher will lead to a bigger reserve which will get freed as contiguous
- * blocks as reclaim kicks in
- */
-static void setup_zone_migrate_reserve(struct zone *zone)
-{
-       unsigned long start_pfn, pfn, end_pfn, block_end_pfn;
-       struct page *page;
-       unsigned long block_migratetype;
-       int reserve;
-       int old_reserve;
-
-       /*
-        * Get the start pfn, end pfn and the number of blocks to reserve
-        * We have to be careful to be aligned to pageblock_nr_pages to
-        * make sure that we always check pfn_valid for the first page in
-        * the block.
-        */
-       start_pfn = zone->zone_start_pfn;
-       end_pfn = zone_end_pfn(zone);
-       start_pfn = roundup(start_pfn, pageblock_nr_pages);
-       reserve = roundup(min_wmark_pages(zone), pageblock_nr_pages) >>
-                                                       pageblock_order;
-
-       /*
-        * Reserve blocks are generally in place to help high-order atomic
-        * allocations that are short-lived. A min_free_kbytes value that
-        * would result in more than 2 reserve blocks for atomic allocations
-        * is assumed to be in place to help anti-fragmentation for the
-        * future allocation of hugepages at runtime.
-        */
-       reserve = min(2, reserve);
-       old_reserve = zone->nr_migrate_reserve_block;
-
-       /* When memory hot-add, we almost always need to do nothing */
-       if (reserve == old_reserve)
-               return;
-       zone->nr_migrate_reserve_block = reserve;
-
-       for (pfn = start_pfn; pfn < end_pfn; pfn += pageblock_nr_pages) {
-               if (!early_page_nid_uninitialised(pfn, zone_to_nid(zone)))
-                       return;
-
-               if (!pfn_valid(pfn))
-                       continue;
-               page = pfn_to_page(pfn);
-
-               /* Watch out for overlapping nodes */
-               if (page_to_nid(page) != zone_to_nid(zone))
-                       continue;
-
-               block_migratetype = get_pageblock_migratetype(page);
-
-               /* Only test what is necessary when the reserves are not met */
-               if (reserve > 0) {
-                       /*
-                        * Blocks with reserved pages will never free, skip
-                        * them.
-                        */
-                       block_end_pfn = min(pfn + pageblock_nr_pages, end_pfn);
-                       if (pageblock_is_reserved(pfn, block_end_pfn))
-                               continue;
-
-                       /* If this block is reserved, account for it */
-                       if (block_migratetype == MIGRATE_RESERVE) {
-                               reserve--;
-                               continue;
-                       }
-
-                       /* Suitable for reserving if this block is movable */
-                       if (block_migratetype == MIGRATE_MOVABLE) {
-                               set_pageblock_migratetype(page,
-                                                       MIGRATE_RESERVE);
-                               move_freepages_block(zone, page,
-                                                       MIGRATE_RESERVE);
-                               reserve--;
-                               continue;
-                       }
-               } else if (!old_reserve) {
-                       /*
-                        * At boot time we don't need to scan the whole zone
-                        * for turning off MIGRATE_RESERVE.
-                        */
-                       break;
-               }
-
-               /*
-                * If the reserve is met and this is a previous reserved block,
-                * take it back
-                */
-               if (block_migratetype == MIGRATE_RESERVE) {
-                       set_pageblock_migratetype(page, MIGRATE_MOVABLE);
-                       move_freepages_block(zone, page, MIGRATE_MOVABLE);
-               }
-       }
-}
-
 /*
  * Initially all pages are reserved - free ones are freed
  * up by free_all_bootmem() once the early boot process is
@@ -4455,9 +4326,7 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
                 * movable at startup. This will force kernel allocations
                 * to reserve their blocks rather than leaking throughout
                 * the address space during boot when many long-lived
-                * kernel allocations are made. Later some blocks near
-                * the start are marked MIGRATE_RESERVE by
-                * setup_zone_migrate_reserve()
+                * kernel allocations are made.
                 *
                 * bitmap is created for zone's valid pfn range. but memmap
                 * can be created for invalid pages (for alignment)
@@ -6018,7 +5887,6 @@ static void __setup_per_zone_wmarks(void)
                        high_wmark_pages(zone) - low_wmark_pages(zone) -
                        atomic_long_read(&zone->vm_stat[NR_ALLOC_BATCH]));
 
-               setup_zone_migrate_reserve(zone);
                spin_unlock_irqrestore(&zone->lock, flags);
        }
 

diff --git a/mm/vmstat.c b/mm/vmstat.c
index ffcb4f5..5b289dc 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -923,7 +923,6 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
        "Unmovable",
        "Reclaimable",
        "Movable",
-       "Reserve",
 #ifdef CONFIG_CMA
        "CMA",
 #endif