mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks

When MIGRATE_UNMOVABLE pages are freed from MIGRATE_UNMOVABLE type
pageblock (and some MIGRATE_MOVABLE pages are left in it) waiting until an
allocation takes ownership of the block may take too long.  The type of
the pageblock remains unchanged so the pageblock cannot be used as a
migration target during compaction.

Fix it by:

* Adding enum compact_mode (COMPACT_ASYNC_[MOVABLE,UNMOVABLE], and
  COMPACT_SYNC) and then converting sync field in struct compact_control
  to use it.

* Adding nr_pageblocks_skipped field to struct compact_control and
  tracking how many destination pageblocks were of MIGRATE_UNMOVABLE type.
   If COMPACT_ASYNC_MOVABLE mode compaction ran fully in
  try_to_compact_pages() (COMPACT_COMPLETE) it implies that there is not a
  suitable page for allocation.  In this case then check how if there were
  enough MIGRATE_UNMOVABLE pageblocks to try a second pass in
  COMPACT_ASYNC_UNMOVABLE mode.

* Scanning the MIGRATE_UNMOVABLE pageblocks (during COMPACT_SYNC and
  COMPACT_ASYNC_UNMOVABLE compaction modes) and building a count based on
  finding PageBuddy pages, page_count(page) == 0 or PageLRU pages.  If all
  pages within the MIGRATE_UNMOVABLE pageblock are in one of those three
  sets change the whole pageblock type to MIGRATE_MOVABLE.

My particular test case (on a ARM EXYNOS4 device with 512 MiB, which means
131072 standard 4KiB pages in 'Normal' zone) is to:

- allocate 120000 pages for kernel's usage
- free every second page (60000 pages) of memory just allocated
- allocate and use 60000 pages from user space
- free remaining 60000 pages of kernel memory
  (now we have fragmented memory occupied mostly by user space pages)
- try to allocate 100 order-9 (2048 KiB) pages for kernel's usage

The results:
- with compaction disabled I get 11 successful allocations
- with compaction enabled - 14 successful allocations
- with this patch I'm able to get all 100 successful allocations

NOTE: If we can make kswapd aware of order-0 request during compaction, we
can enhance kswapd with changing mode to COMPACT_ASYNC_FULL
(COMPACT_ASYNC_MOVABLE + COMPACT_ASYNC_UNMOVABLE).  Please see the
following thread:

	http://marc.info/?l=linux-mm&m=133552069417068&w=2

[minchan@kernel.org: minor cleanups]
Cc: Mel Gorman <mgorman@suse.de>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Rik van Riel <riel@redhat.com>
Cc: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/compaction.h

@@ -1,6 +1,8 @@
 #ifndef _LINUX_COMPACTION_H
 #define _LINUX_COMPACTION_H
 
+#include <linux/node.h>
+
 /* Return values for compact_zone() and try_to_compact_pages() */
 /* compaction didn't start as it was not possible or direct reclaim was more suitable */
 #define COMPACT_SKIPPED		0
@@ -11,6 +13,23 @@
 /* The full zone was compacted */
 #define COMPACT_COMPLETE	3
 
+/*
+ * compaction supports three modes
+ *
+ * COMPACT_ASYNC_MOVABLE uses asynchronous migration and only scans
+ *    MIGRATE_MOVABLE pageblocks as migration sources and targets.
+ * COMPACT_ASYNC_UNMOVABLE uses asynchronous migration and only scans
+ *    MIGRATE_MOVABLE pageblocks as migration sources.
+ *    MIGRATE_UNMOVABLE pageblocks are scanned as potential migration
+ *    targets and convers them to MIGRATE_MOVABLE if possible
+ * COMPACT_SYNC uses synchronous migration and scans all pageblocks
+ */
+enum compact_mode {
+	COMPACT_ASYNC_MOVABLE,
+	COMPACT_ASYNC_UNMOVABLE,
+	COMPACT_SYNC,
+};
+
 #ifdef CONFIG_COMPACTION
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,

mm/compaction.c

@@ -235,7 +235,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 	 */
 	while (unlikely(too_many_isolated(zone))) {
 		/* async migration should just abort */
-		if (!cc->sync)
+		if (cc->mode != COMPACT_SYNC)
 			return 0;
 
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
@@ -303,7 +303,8 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 		 * satisfies the allocation
 		 */
 		pageblock_nr = low_pfn >> pageblock_order;
-		if (!cc->sync && last_pageblock_nr != pageblock_nr &&
+		if (cc->mode != COMPACT_SYNC &&
+		    last_pageblock_nr != pageblock_nr &&
 		    !migrate_async_suitable(get_pageblock_migratetype(page))) {
 			low_pfn += pageblock_nr_pages;
 			low_pfn = ALIGN(low_pfn, pageblock_nr_pages) - 1;
@@ -324,7 +325,7 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 			continue;
 		}
 
-		if (!cc->sync)
+		if (cc->mode != COMPACT_SYNC)
 			mode |= ISOLATE_ASYNC_MIGRATE;
 
 		/* Try isolate the page */
@@ -357,27 +358,90 @@ isolate_migratepages_range(struct zone *zone, struct compact_control *cc,
 
 #endif /* CONFIG_COMPACTION || CONFIG_CMA */
 #ifdef CONFIG_COMPACTION
+/*
+ * Returns true if MIGRATE_UNMOVABLE pageblock was successfully
+ * converted to MIGRATE_MOVABLE type, false otherwise.
+ */
+static bool rescue_unmovable_pageblock(struct page *page)
+{
+	unsigned long pfn, start_pfn, end_pfn;
+	struct page *start_page, *end_page;
+
+	pfn = page_to_pfn(page);
+	start_pfn = pfn & ~(pageblock_nr_pages - 1);
+	end_pfn = start_pfn + pageblock_nr_pages;
+
+	start_page = pfn_to_page(start_pfn);
+	end_page = pfn_to_page(end_pfn);
+
+	/* Do not deal with pageblocks that overlap zones */
+	if (page_zone(start_page) != page_zone(end_page))
+		return false;
+
+	for (page = start_page, pfn = start_pfn; page < end_page; pfn++,
+								  page++) {
+		if (!pfn_valid_within(pfn))
+			continue;
+
+		if (PageBuddy(page)) {
+			int order = page_order(page);
+
+			pfn += (1 << order) - 1;
+			page += (1 << order) - 1;
+
+			continue;
+		} else if (page_count(page) == 0 || PageLRU(page))
+			continue;
+
+		return false;
+	}
+
+	set_pageblock_migratetype(page, MIGRATE_MOVABLE);
+	move_freepages_block(page_zone(page), page, MIGRATE_MOVABLE);
+	return true;
+}
 
-/* Returns true if the page is within a block suitable for migration to */
-static bool suitable_migration_target(struct page *page)
+enum smt_result {
+	GOOD_AS_MIGRATION_TARGET,
+	FAIL_UNMOVABLE_TARGET,
+	FAIL_BAD_TARGET,
+};
+
+/*
+ * Returns GOOD_AS_MIGRATION_TARGET if the page is within a block
+ * suitable for migration to, FAIL_UNMOVABLE_TARGET if the page
+ * is within a MIGRATE_UNMOVABLE block, FAIL_BAD_TARGET otherwise.
+ */
+static enum smt_result suitable_migration_target(struct page *page,
+				      struct compact_control *cc)
 {
 
 	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;
+		return FAIL_BAD_TARGET;
 
 	/* If the page is a large free page, then allow migration */
 	if (PageBuddy(page) && page_order(page) >= pageblock_order)
-		return true;
+		return GOOD_AS_MIGRATION_TARGET;
 
 	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
-	if (migrate_async_suitable(migratetype))
-		return true;
+	if (cc->mode != COMPACT_ASYNC_UNMOVABLE &&
+	    migrate_async_suitable(migratetype))
+		return GOOD_AS_MIGRATION_TARGET;
+
+	if (cc->mode == COMPACT_ASYNC_MOVABLE &&
+	    migratetype == MIGRATE_UNMOVABLE)
+		return FAIL_UNMOVABLE_TARGET;
+
+	if (cc->mode != COMPACT_ASYNC_MOVABLE &&
+	    migratetype == MIGRATE_UNMOVABLE &&
+	    rescue_unmovable_pageblock(page))
+		return GOOD_AS_MIGRATION_TARGET;
 
 	/* Otherwise skip the block */
-	return false;
+	return FAIL_BAD_TARGET;
 }
 
 /*
@@ -410,6 +474,13 @@ static void isolate_freepages(struct zone *zone,
 
 	zone_end_pfn = zone->zone_start_pfn + zone->spanned_pages;
 
+	/*
+	 * isolate_freepages() may be called more than once during
+	 * compact_zone_order() run and we want only the most recent
+	 * count.
+	 */
+	cc->nr_pageblocks_skipped = 0;
+
 	/*
 	 * Isolate free pages until enough are available to migrate the
 	 * pages on cc->migratepages. We stop searching if the migrate
@@ -418,6 +489,7 @@ static void isolate_freepages(struct zone *zone,
 	for (; pfn > low_pfn && cc->nr_migratepages > nr_freepages;
 					pfn -= pageblock_nr_pages) {
 		unsigned long isolated;
+		enum smt_result ret;
 
 		if (!pfn_valid(pfn))
 			continue;
@@ -434,9 +506,12 @@ static void isolate_freepages(struct zone *zone,
 			continue;
 
 		/* Check the block is suitable for migration */
-		if (!suitable_migration_target(page))
+		ret = suitable_migration_target(page, cc);
+		if (ret != GOOD_AS_MIGRATION_TARGET) {
+			if (ret == FAIL_UNMOVABLE_TARGET)
+				cc->nr_pageblocks_skipped++;
 			continue;
-
+		}
 		/*
 		 * Found a block suitable for isolating free pages from. Now
 		 * we disabled interrupts, double check things are ok and
@@ -445,12 +520,14 @@ static void isolate_freepages(struct zone *zone,
 		 */
 		isolated = 0;
 		spin_lock_irqsave(&zone->lock, flags);
-		if (suitable_migration_target(page)) {
+		ret = suitable_migration_target(page, cc);
+		if (ret == GOOD_AS_MIGRATION_TARGET) {
 			end_pfn = min(pfn + pageblock_nr_pages, zone_end_pfn);
 			isolated = isolate_freepages_block(pfn, end_pfn,
 							   freelist, false);
 			nr_freepages += isolated;
-		}
+		} else if (ret == FAIL_UNMOVABLE_TARGET)
+			cc->nr_pageblocks_skipped++;
 		spin_unlock_irqrestore(&zone->lock, flags);
 
 		/*
@@ -682,8 +759,9 @@ static int compact_zone(struct zone *zone, struct compact_control *cc)
 
 		nr_migrate = cc->nr_migratepages;
 		err = migrate_pages(&cc->migratepages, compaction_alloc,
-				(unsigned long)cc, false,
-				cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
+			(unsigned long)&cc->freepages, false,
+			(cc->mode == COMPACT_SYNC) ? MIGRATE_SYNC_LIGHT
+						      : MIGRATE_ASYNC);
 		update_nr_listpages(cc);
 		nr_remaining = cc->nr_migratepages;
 
@@ -712,7 +790,8 @@ out:
 
 static unsigned long compact_zone_order(struct zone *zone,
 				 int order, gfp_t gfp_mask,
-				 bool sync)
+				 enum compact_mode mode,
+				 unsigned long *nr_pageblocks_skipped)
 {
 	struct compact_control cc = {
 		.nr_freepages = 0,
@@ -720,12 +799,17 @@ static unsigned long compact_zone_order(struct zone *zone,
 		.order = order,
 		.migratetype = allocflags_to_migratetype(gfp_mask),
 		.zone = zone,
-		.sync = sync,
+		.mode = mode,
 	};
+	unsigned long rc;
+
 	INIT_LIST_HEAD(&cc.freepages);
 	INIT_LIST_HEAD(&cc.migratepages);
 
-	return compact_zone(zone, &cc);
+	rc = compact_zone(zone, &cc);
+	*nr_pageblocks_skipped = cc.nr_pageblocks_skipped;
+
+	return rc;
 }
 
 int sysctl_extfrag_threshold = 500;
@@ -750,6 +834,8 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
 	struct zoneref *z;
 	struct zone *zone;
 	int rc = COMPACT_SKIPPED;
+	unsigned long nr_pageblocks_skipped;
+	enum compact_mode mode;
 
 	/*
 	 * Check whether it is worth even starting compaction. The order check is
@@ -766,12 +852,22 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
 								nodemask) {
 		int status;
 
-		status = compact_zone_order(zone, order, gfp_mask, sync);
+		mode = sync ? COMPACT_SYNC : COMPACT_ASYNC_MOVABLE;
+retry:
+		status = compact_zone_order(zone, order, gfp_mask, mode,
+						&nr_pageblocks_skipped);
 		rc = max(status, rc);
 
 		/* If a normal allocation would succeed, stop compacting */
 		if (zone_watermark_ok(zone, order, low_wmark_pages(zone), 0, 0))
 			break;
+
+		if (rc == COMPACT_COMPLETE && mode == COMPACT_ASYNC_MOVABLE) {
+			if (nr_pageblocks_skipped) {
+				mode = COMPACT_ASYNC_UNMOVABLE;
+				goto retry;
+			}
+		}
 	}
 
 	return rc;
@@ -805,7 +901,7 @@ static int __compact_pgdat(pg_data_t *pgdat, struct compact_control *cc)
 			if (ok && cc->order > zone->compact_order_failed)
 				zone->compact_order_failed = cc->order + 1;
 			/* Currently async compaction is never deferred. */
-			else if (!ok && cc->sync)
+			else if (!ok && cc->mode == COMPACT_SYNC)
 				defer_compaction(zone, cc->order);
 		}
 
@@ -820,7 +916,7 @@ int compact_pgdat(pg_data_t *pgdat, int order)
 {
 	struct compact_control cc = {
 		.order = order,
-		.sync = false,
+		.mode = COMPACT_ASYNC_MOVABLE,
 	};
 
 	return __compact_pgdat(pgdat, &cc);
@@ -830,7 +926,7 @@ static int compact_node(int nid)
 {
 	struct compact_control cc = {
 		.order = -1,
-		.sync = true,
+		.mode = COMPACT_SYNC,
 	};
 
 	return __compact_pgdat(NODE_DATA(nid), &cc);

mm/internal.h

@@ -94,6 +94,9 @@ extern void putback_lru_page(struct page *page);
 /*
  * in mm/page_alloc.c
  */
+extern void set_pageblock_migratetype(struct page *page, int migratetype);
+extern int move_freepages_block(struct zone *zone, struct page *page,
+				int migratetype);
 extern void __free_pages_bootmem(struct page *page, unsigned int order);
 extern void prep_compound_page(struct page *page, unsigned long order);
 #ifdef CONFIG_MEMORY_FAILURE
@@ -101,6 +104,7 @@ extern bool is_free_buddy_page(struct page *page);
 #endif
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
+#include <linux/compaction.h>
 
 /*
  * in mm/compaction.c
@@ -119,11 +123,14 @@ struct compact_control {
 	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 */
-	bool sync;			/* Synchronous migration */
+	enum compact_mode mode;		/* Compaction mode */
 
 	int order;			/* order a direct compactor needs */
 	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
 	struct zone *zone;
+
+	/* Number of UNMOVABLE destination pageblocks skipped during scan */
+	unsigned long nr_pageblocks_skipped;
 };
 
 unsigned long

mm/page_alloc.c

@@ -219,7 +219,7 @@ EXPORT_SYMBOL(nr_online_nodes);
 
 int page_group_by_mobility_disabled __read_mostly;
 
-static void set_pageblock_migratetype(struct page *page, int migratetype)
+void set_pageblock_migratetype(struct page *page, int migratetype)
 {
 
 	if (unlikely(page_group_by_mobility_disabled))
@@ -954,8 +954,8 @@ static int move_freepages(struct zone *zone,
 	return pages_moved;
 }
 
-static int move_freepages_block(struct zone *zone, struct page *page,
-				int migratetype)
+int move_freepages_block(struct zone *zone, struct page *page,
+			 int migratetype)
 {
 	unsigned long start_pfn, end_pfn;
 	struct page *start_page, *end_page;
@@ -5657,7 +5657,7 @@ static int __alloc_contig_migrate_range(unsigned long start, unsigned long end)
 		.nr_migratepages = 0,
 		.order = -1,
 		.zone = page_zone(pfn_to_page(start)),
-		.sync = true,
+		.mode = COMPACT_SYNC,
 	};
 	INIT_LIST_HEAD(&cc.migratepages);