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>

1 files changed, 8 insertions, 140 deletions

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 8dc6e3cd40f0..588812614377 100644
--- 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
@@ -4303,120 +4288,6 @@ static inline unsigned long wait_table_bits(unsigned long 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
  * done. Non-atomic initialization, single-pass.
@@ -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);
         }