mm: compaction: memory compaction core

This patch is the core of a mechanism which compacts memory in a zone by
relocating movable pages towards the end of the zone.

A single compaction run involves a migration scanner and a free scanner.
Both scanners operate on pageblock-sized areas in the zone.  The migration
scanner starts at the bottom of the zone and searches for all movable
pages within each area, isolating them onto a private list called
migratelist.  The free scanner starts at the top of the zone and searches
for suitable areas and consumes the free pages within making them
available for the migration scanner.  The pages isolated for migration are
then migrated to the newly isolated free pages.

[aarcange@redhat.com: Fix unsafe optimisation]
[mel@csn.ul.ie: do not schedule work on other CPUs for compaction]
Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Acked-by: Rik van Riel <riel@redhat.com>
Reviewed-by: Minchan Kim <minchan.kim@gmail.com>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Christoph Lameter <cl@linux-foundation.org>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

10 files changed, 472 insertions, 1 deletions

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
new file mode 100644
index 000000000000..465ca88615ed
--- /dev/null
+++ b/include/linux/compaction.h
@@ -0,0 +1,9 @@
+#ifndef _LINUX_COMPACTION_H
+#define _LINUX_COMPACTION_H
+
+/* Return values for compact_zone() */
+#define COMPACT_CONTINUE        0
+#define COMPACT_PARTIAL         1
+#define COMPACT_COMPLETE        2
+
+#endif /* _LINUX_COMPACTION_H */
diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index 7a07b17d27c5..7238231b8dd4 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -19,6 +19,7 @@ extern int fail_migrate_page(struct address_space *,
                         struct page *, struct page *);
 
 extern int migrate_prep(void);
+extern int migrate_prep_local(void);
 extern int migrate_vmas(struct mm_struct *mm,
                 const nodemask_t *from, const nodemask_t *to,
                 unsigned long flags);
@@ -30,6 +31,7 @@ static inline int migrate_pages(struct list_head *l, new_page_t x,
                 unsigned long private, int offlining) { return -ENOSYS; }
 
 static inline int migrate_prep(void) { return -ENOSYS; }
+static inline int migrate_prep_local(void) { return -ENOSYS; }
 
 static inline int migrate_vmas(struct mm_struct *mm,
                 const nodemask_t *from, const nodemask_t *to,
diff --git a/include/linux/mm.h b/include/linux/mm.h
index 98ea5bab963e..963f908af9d0 100644
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -337,6 +337,7 @@ void put_page(struct page *page);
 void put_pages_list(struct list_head *pages);
 
 void split_page(struct page *page, unsigned int order);
+int split_free_page(struct page *page);
 
 /*
  * Compound pages have a destructor function.  Provide a
diff --git a/include/linux/swap.h b/include/linux/swap.h
index 1e8ce148d058..b6b614364dd8 100644
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -152,6 +152,7 @@ enum {
 };
 
 #define SWAP_CLUSTER_MAX 32
+#define COMPACT_CLUSTER_MAX SWAP_CLUSTER_MAX
 
 #define SWAP_MAP_MAX    0x3e    /* Max duplication count, in first swap_map */
 #define SWAP_MAP_BAD    0x3f    /* Note pageblock is bad, in first swap_map */
diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 117f0dd8ad03..b421d1b22b62 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -43,6 +43,9 @@ enum vm_event_item { PGPGIN, PGPGOUT, PSWPIN, PSWPOUT,
                 KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
                 KSWAPD_SKIP_CONGESTION_WAIT,
                 PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+#ifdef CONFIG_COMPACTION
+                COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
+#endif
 #ifdef CONFIG_HUGETLB_PAGE
                 HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
 #endif
diff --git a/mm/Makefile b/mm/Makefile
index 6c2a73a54a43..8982504bd03b 100644
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -23,6 +23,7 @@ obj-$(CONFIG_NUMA) 	+= mempolicy.o
 obj-$(CONFIG_SPARSEMEM) += sparse.o
 obj-$(CONFIG_SPARSEMEM_VMEMMAP) += sparse-vmemmap.o
 obj-$(CONFIG_SLOB) += slob.o
+obj-$(CONFIG_COMPACTION) += compaction.o
 obj-$(CONFIG_MMU_NOTIFIER) += mmu_notifier.o
 obj-$(CONFIG_KSM) += ksm.o
 obj-$(CONFIG_PAGE_POISONING) += debug-pagealloc.o
diff --git a/mm/compaction.c b/mm/compaction.c
new file mode 100644
index 000000000000..be1ff3f7552b
--- /dev/null
+++ b/mm/compaction.c
@@ -0,0 +1,393 @@
+/*
+ * linux/mm/compaction.c
+ *
+ * Memory compaction for the reduction of external fragmentation. Note that
+ * this heavily depends upon page migration to do all the real heavy
+ * lifting
+ *
+ * Copyright IBM Corp. 2007-2010 Mel Gorman <mel@csn.ul.ie>
+ */
+#include <linux/swap.h>
+#include <linux/migrate.h>
+#include <linux/compaction.h>
+#include <linux/mm_inline.h>
+#include <linux/backing-dev.h>
+#include "internal.h"
+
+/*
+ * compact_control is used to track pages being migrated and the free pages
+ * they are being migrated to during memory compaction. The free_pfn starts
+ * at the end of a zone and migrate_pfn begins at the start. Movable pages
+ * are moved to the end of a zone during a compaction run and the run
+ * completes when free_pfn <= migrate_pfn
+ */
+struct compact_control {
+        struct list_head freepages;     /* List of free pages to migrate to */
+        struct list_head migratepages;  /* List of pages being migrated */
+        unsigned long nr_freepages;     /* Number of isolated free pages */
+        unsigned long nr_migratepages;  /* Number of pages to migrate */
+        unsigned long free_pfn;         /* isolate_freepages search base */
+        unsigned long migrate_pfn;      /* isolate_migratepages search base */
+
+        /* Account for isolated anon and file pages */
+        unsigned long nr_anon;
+        unsigned long nr_file;
+
+        struct zone *zone;
+};
+
+static unsigned long release_freepages(struct list_head *freelist)
+{
+        struct page *page, *next;
+        unsigned long count = 0;
+
+        list_for_each_entry_safe(page, next, freelist, lru) {
+                list_del(&page->lru);
+                __free_page(page);
+                count++;
+        }
+
+        return count;
+}
+
+/* Isolate free pages onto a private freelist. Must hold zone->lock */
+static unsigned long isolate_freepages_block(struct zone *zone,
+                                unsigned long blockpfn,
+                                struct list_head *freelist)
+{
+        unsigned long zone_end_pfn, end_pfn;
+        int total_isolated = 0;
+        struct page *cursor;
+
+        /* Get the last PFN we should scan for free pages at */
+        zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
+        end_pfn = min(blockpfn + pageblock_nr_pages, zone_end_pfn);
+
+        /* Find the first usable PFN in the block to initialse page cursor */
+        for (; blockpfn < end_pfn; blockpfn++) {
+                if (pfn_valid_within(blockpfn))
+                        break;
+        }
+        cursor = pfn_to_page(blockpfn);
+
+        /* Isolate free pages. This assumes the block is valid */
+        for (; blockpfn < end_pfn; blockpfn++, cursor++) {
+                int isolated, i;
+                struct page *page = cursor;
+
+                if (!pfn_valid_within(blockpfn))
+                        continue;
+
+                if (!PageBuddy(page))
+                        continue;
+
+                /* Found a free page, break it into order-0 pages */
+                isolated = split_free_page(page);
+                total_isolated += isolated;
+                for (i = 0; i < isolated; i++) {
+                        list_add(&page->lru, freelist);
+                        page++;
+                }
+
+                /* If a page was split, advance to the end of it */
+                if (isolated) {
+                        blockpfn += isolated - 1;
+                        cursor += isolated - 1;
+                }
+        }
+
+        return total_isolated;
+}
+
+/* Returns true if the page is within a block suitable for migration to */
+static bool suitable_migration_target(struct page *page)
+{
+
+        int migratetype = get_pageblock_migratetype(page);
+
+        /* Don't interfere with memory hot-remove or the min_free_kbytes blocks */
+        if (migratetype == MIGRATE_ISOLATE || migratetype == MIGRATE_RESERVE)
+                return false;
+
+        /* If the page is a large free page, then allow migration */
+        if (PageBuddy(page) && page_order(page) >= pageblock_order)
+                return true;
+
+        /* If the block is MIGRATE_MOVABLE, allow migration */
+        if (migratetype == MIGRATE_MOVABLE)
+                return true;
+
+        /* Otherwise skip the block */
+        return false;
+}
+
+/*
+ * Based on information in the current compact_control, find blocks
+ * suitable for isolating free pages from and then isolate them.
+ */
+static void isolate_freepages(struct zone *zone,
+                                struct compact_control *cc)
+{
+        struct page *page;
+        unsigned long high_pfn, low_pfn, pfn;
+        unsigned long flags;
+        int nr_freepages = cc->nr_freepages;
+        struct list_head *freelist = &cc->freepages;
+
+        pfn = cc->free_pfn;
+        low_pfn = cc->migrate_pfn + pageblock_nr_pages;
+        high_pfn = low_pfn;
+
+        /*
+         * Isolate free pages until enough are available to migrate the
+         * pages on cc->migratepages. We stop searching if the migrate
+         * and free page scanners meet or enough free pages are isolated.
+         */
+        spin_lock_irqsave(&zone->lock, flags);
+        for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
+                                        pfn -= pageblock_nr_pages) {
+                unsigned long isolated;
+
+                if (!pfn_valid(pfn))
+                        continue;
+
+                /*
+                 * Check for overlapping nodes/zones. It's possible on some
+                 * configurations to have a setup like
+                 * node0 node1 node0
+                 * i.e. it's possible that all pages within a zones range of
+                 * pages do not belong to a single zone.
+                 */
+                page = pfn_to_page(pfn);
+                if (page_zone(page) != zone)
+                        continue;
+
+                /* Check the block is suitable for migration */
+                if (!suitable_migration_target(page))
+                        continue;
+
+                /* Found a block suitable for isolating free pages from */
+                isolated = isolate_freepages_block(zone, pfn, freelist);
+                nr_freepages += isolated;
+
+                /*
+                 * Record the highest PFN we isolated pages from. When next
+                 * looking for free pages, the search will restart here as
+                 * page migration may have returned some pages to the allocator
+                 */
+                if (isolated)
+                        high_pfn = max(high_pfn, pfn);
+        }
+        spin_unlock_irqrestore(&zone->lock, flags);
+
+        /* split_free_page does not map the pages */
+        list_for_each_entry(page, freelist, lru) {
+                arch_alloc_page(page, 0);
+                kernel_map_pages(page, 1, 1);
+        }
+
+        cc->free_pfn = high_pfn;
+        cc->nr_freepages = nr_freepages;
+}
+
+/* Update the number of anon and file isolated pages in the zone */
+static void acct_isolated(struct zone *zone, struct compact_control *cc)
+{
+        struct page *page;
+        unsigned int count[NR_LRU_LISTS] = { 0, };
+
+        list_for_each_entry(page, &cc->migratepages, lru) {
+                int lru = page_lru_base_type(page);
+                count[lru]++;
+        }
+
+        cc->nr_anon = count[LRU_ACTIVE_ANON] + count[LRU_INACTIVE_ANON];
+        cc->nr_file = count[LRU_ACTIVE_FILE] + count[LRU_INACTIVE_FILE];
+        __mod_zone_page_state(zone, NR_ISOLATED_ANON, cc->nr_anon);
+        __mod_zone_page_state(zone, NR_ISOLATED_FILE, cc->nr_file);
+}
+
+/* Similar to reclaim, but different enough that they don't share logic */
+static bool too_many_isolated(struct zone *zone)
+{
+
+        unsigned long inactive, isolated;
+
+        inactive = zone_page_state(zone, NR_INACTIVE_FILE) +
+                                        zone_page_state(zone, NR_INACTIVE_ANON);
+        isolated = zone_page_state(zone, NR_ISOLATED_FILE) +
+                                        zone_page_state(zone, NR_ISOLATED_ANON);
+
+        return isolated > inactive;
+}
+
+/*
+ * Isolate all pages that can be migrated from the block pointed to by
+ * the migrate scanner within compact_control.
+ */
+static unsigned long isolate_migratepages(struct zone *zone,
+                                        struct compact_control *cc)
+{
+        unsigned long low_pfn, end_pfn;
+        struct list_head *migratelist = &cc->migratepages;
+
+        /* Do not scan outside zone boundaries */
+        low_pfn = max(cc->migrate_pfn, zone->zone_start_pfn);
+
+        /* Only scan within a pageblock boundary */
+        end_pfn = ALIGN(low_pfn + pageblock_nr_pages, pageblock_nr_pages);
+
+        /* Do not cross the free scanner or scan within a memory hole */
+        if (end_pfn > cc->free_pfn || !pfn_valid(low_pfn)) {
+                cc->migrate_pfn = end_pfn;
+                return 0;
+        }
+
+        /*
+         * Ensure that there are not too many pages isolated from the LRU
+         * list by either parallel reclaimers or compaction. If there are,
+         * delay for some time until fewer pages are isolated
+         */
+        while (unlikely(too_many_isolated(zone))) {
+                congestion_wait(BLK_RW_ASYNC, HZ/10);
+
+                if (fatal_signal_pending(current))
+                        return 0;
+        }
+
+        /* Time to isolate some pages for migration */
+        spin_lock_irq(&zone->lru_lock);
+        for (; low_pfn < end_pfn; low_pfn++) {
+                struct page *page;
+                if (!pfn_valid_within(low_pfn))
+                        continue;
+
+                /* Get the page and skip if free */
+                page = pfn_to_page(low_pfn);
+                if (PageBuddy(page))
+                        continue;
+
+                /* Try isolate the page */
+                if (__isolate_lru_page(page, ISOLATE_BOTH, 0) != 0)
+                        continue;
+
+                /* Successfully isolated */
+                del_page_from_lru_list(zone, page, page_lru(page));
+                list_add(&page->lru, migratelist);
+                mem_cgroup_del_lru(page);
+                cc->nr_migratepages++;
+
+                /* Avoid isolating too much */
+                if (cc->nr_migratepages == COMPACT_CLUSTER_MAX)
+                        break;
+        }
+
+        acct_isolated(zone, cc);
+
+        spin_unlock_irq(&zone->lru_lock);
+        cc->migrate_pfn = low_pfn;
+
+        return cc->nr_migratepages;
+}
+
+/*
+ * This is a migrate-callback that "allocates" freepages by taking pages
+ * from the isolated freelists in the block we are migrating to.
+ */
+static struct page *compaction_alloc(struct page *migratepage,
+                                        unsigned long data,
+                                        int **result)
+{
+        struct compact_control *cc = (struct compact_control *)data;
+        struct page *freepage;
+
+        /* Isolate free pages if necessary */
+        if (list_empty(&cc->freepages)) {
+                isolate_freepages(cc->zone, cc);
+
+                if (list_empty(&cc->freepages))
+                        return NULL;
+        }
+
+        freepage = list_entry(cc->freepages.next, struct page, lru);
+        list_del(&freepage->lru);
+        cc->nr_freepages--;
+
+        return freepage;
+}
+
+/*
+ * We cannot control nr_migratepages and nr_freepages fully when migration is
+ * running as migrate_pages() has no knowledge of compact_control. When
+ * migration is complete, we count the number of pages on the lists by hand.
+ */
+static void update_nr_listpages(struct compact_control *cc)
+{
+        int nr_migratepages = 0;
+        int nr_freepages = 0;
+        struct page *page;
+
+        list_for_each_entry(page, &cc->migratepages, lru)
+                nr_migratepages++;
+        list_for_each_entry(page, &cc->freepages, lru)
+                nr_freepages++;
+
+        cc->nr_migratepages = nr_migratepages;
+        cc->nr_freepages = nr_freepages;
+}
+
+static int compact_finished(struct zone *zone,
+                                                struct compact_control *cc)
+{
+        if (fatal_signal_pending(current))
+                return COMPACT_PARTIAL;
+
+        /* Compaction run completes if the migrate and free scanner meet */
+        if (cc->free_pfn <= cc->migrate_pfn)
+                return COMPACT_COMPLETE;
+
+        return COMPACT_CONTINUE;
+}
+
+static int compact_zone(struct zone *zone, struct compact_control *cc)
+{
+        int ret;
+
+        /* Setup to move all movable pages to the end of the zone */
+        cc->migrate_pfn = zone->zone_start_pfn;
+        cc->free_pfn = cc->migrate_pfn + zone->spanned_pages;
+        cc->free_pfn &= ~(pageblock_nr_pages-1);
+
+        migrate_prep_local();
+
+        while ((ret = compact_finished(zone, cc)) == COMPACT_CONTINUE) {
+                unsigned long nr_migrate, nr_remaining;
+
+                if (!isolate_migratepages(zone, cc))
+                        continue;
+
+                nr_migrate = cc->nr_migratepages;
+                migrate_pages(&cc->migratepages, compaction_alloc,
+                                                (unsigned long)cc, 0);
+                update_nr_listpages(cc);
+                nr_remaining = cc->nr_migratepages;
+
+                count_vm_event(COMPACTBLOCKS);
+                count_vm_events(COMPACTPAGES, nr_migrate - nr_remaining);
+                if (nr_remaining)
+                        count_vm_events(COMPACTPAGEFAILED, nr_remaining);
+
+                /* Release LRU pages not migrated */
+                if (!list_empty(&cc->migratepages)) {
+                        putback_lru_pages(&cc->migratepages);
+                        cc->nr_migratepages = 0;
+                }
+
+        }
+
+        /* Release free pages and check accounting */
+        cc->nr_freepages -= release_freepages(&cc->freepages);
+        VM_BUG_ON(cc->nr_freepages != 0);
+
+        return ret;
+}
diff --git a/mm/migrate.c b/mm/migrate.c
index 4afd6fe3c074..09e2471afa0f 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -40,7 +40,8 @@
 
 /*
  * migrate_prep() needs to be called before we start compiling a list of pages
- * to be migrated using isolate_lru_page().
+ * to be migrated using isolate_lru_page(). If scheduling work on other CPUs is
+ * undesirable, use migrate_prep_local()
  */
 int migrate_prep(void)
 {
@@ -55,6 +56,14 @@ int migrate_prep(void)
         return 0;
 }
 
+/* Do the necessary work of migrate_prep but not if it involves other CPUs */
+int migrate_prep_local(void)
+{
+        lru_add_drain();
+
+        return 0;
+}
+
 /*
  * Add isolated pages on the list back to the LRU under page lock
  * to avoid leaking evictable pages back onto unevictable list.
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index cefe6fe8d991..c54376a09f30 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1208,6 +1208,51 @@ void split_page(struct page *page, unsigned int order)
 }
 
 /*
+ * Similar to split_page except the page is already free. As this is only
+ * being used for migration, the migratetype of the block also changes.
+ * As this is called with interrupts disabled, the caller is responsible
+ * for calling arch_alloc_page() and kernel_map_page() after interrupts
+ * are enabled.
+ *
+ * Note: this is probably too low level an operation for use in drivers.
+ * Please consult with lkml before using this in your driver.
+ */
+int split_free_page(struct page *page)
+{
+        unsigned int order;
+        unsigned long watermark;
+        struct zone *zone;
+
+        BUG_ON(!PageBuddy(page));
+
+        zone = page_zone(page);
+        order = page_order(page);
+
+        /* Obey watermarks as if the page was being allocated */
+        watermark = low_wmark_pages(zone) + (1 << order);
+        if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
+                return 0;
+
+        /* Remove page from free list */
+        list_del(&page->lru);
+        zone->free_area[order].nr_free--;
+        rmv_page_order(page);
+        __mod_zone_page_state(zone, NR_FREE_PAGES, -(1UL << order));
+
+        /* Split into individual pages */
+        set_page_refcounted(page);
+        split_page(page, order);
+
+        if (order >= pageblock_order - 1) {
+                struct page *endpage = page + (1 << order) - 1;
+                for (; page < endpage; page += pageblock_nr_pages)
+                        set_pageblock_migratetype(page, MIGRATE_MOVABLE);
+        }
+
+        return 1 << order;
+}
+
+/*
  * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
  * we cheat by calling it from here, in the order > 0 path.  Saves a branch
  * or two.
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 23a5899c7461..c6aacf51b554 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -766,6 +766,13 @@ static const char * const vmstat_text[] = {
         "allocstall",
 
         "pgrotated",
+
+#ifdef CONFIG_COMPACTION
+        "compact_blocks_moved",
+        "compact_pages_moved",
+        "compact_pagemigrate_failed",
+#endif
+
 #ifdef CONFIG_HUGETLB_PAGE
         "htlb_buddy_alloc_success",
         "htlb_buddy_alloc_fail",