[PATCH 56 of 67] Memory compaction core

[Andrea Arcangeli <aarcange@redhat.com>]

From: Mel Gorman <mel@csn.ul.ie>

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.

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>
---

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
new file mode 100644
--- /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_INCOMPLETE	0
+#define COMPACT_PARTIAL		1
+#define COMPACT_COMPLETE	2
+
+#endif /* _LINUX_COMPACTION_H */
diff --git a/include/linux/mm.h b/include/linux/mm.h
--- a/include/linux/mm.h
+++ b/include/linux/mm.h
@@ -384,6 +384,7 @@ 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
--- a/include/linux/swap.h
+++ b/include/linux/swap.h
@@ -151,6 +151,7 @@ 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
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -43,6 +43,7 @@ enum vm_event_item { PGPGIN, PGPGOUT, PS
 		KSWAPD_LOW_WMARK_HIT_QUICKLY, KSWAPD_HIGH_WMARK_HIT_QUICKLY,
 		KSWAPD_SKIP_CONGESTION_WAIT,
 		PAGEOUTRUN, ALLOCSTALL, PGROTATED,
+		COMPACTBLOCKS, COMPACTPAGES, COMPACTPAGEFAILED,
 #ifdef CONFIG_HUGETLB_PAGE
 		HTLB_BUDDY_PGALLOC, HTLB_BUDDY_PGALLOC_FAIL,
 #endif
diff --git a/mm/Makefile b/mm/Makefile
--- a/mm/Makefile
+++ b/mm/Makefile
@@ -33,6 +33,7 @@ obj-$(CONFIG_FAILSLAB) += failslab.o
 obj-$(CONFIG_MEMORY_HOTPLUG) += memory_hotplug.o
 obj-$(CONFIG_FS_XIP) += filemap_xip.o
 obj-$(CONFIG_MIGRATION) += migrate.o
+obj-$(CONFIG_COMPACTION) += compaction.o
 ifdef CONFIG_SMP
 obj-y += percpu.o
 else
diff --git a/mm/compaction.c b/mm/compaction.c
new file mode 100644
--- /dev/null
+++ b/mm/compaction.c
@@ -0,0 +1,390 @@
+/*
+ * 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);
+
+	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)) {
+			low_pfn += (1 << page_order(page)) - 1;
+			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 inline 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_INCOMPLETE;
+}
+
+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();
+
+	while ((ret = compact_finished(zone, cc)) == COMPACT_INCOMPLETE) {
+		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/page_alloc.c b/mm/page_alloc.c
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1191,6 +1191,45 @@ void split_page(struct page *page, unsig
 }
 
 /*
+ * 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.
+ */
+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
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -896,6 +896,11 @@ static const char * const vmstat_text[] 
 	"allocstall",
 
 	"pgrotated",
+
+	"compact_blocks_moved",
+	"compact_pages_moved",
+	"compact_pagemigrate_failed",
+
 #ifdef CONFIG_HUGETLB_PAGE
 	"htlb_buddy_alloc_success",
 	"htlb_buddy_alloc_fail",

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