Revert "mm: compaction: handle incorrect MIGRATE_UNMOVABLE type pageblocks"

This reverts commit 5ceb9ce6fe9462a298bb2cd5c9f1ca6cb80a0199.

That commit seems to be the cause of the mm compation list corruption
issues that Dave Jones reported. The locking (or rather, absense
there-of) is dubious, as is the use of the 'page' variable once it has
been found to be outside the pageblock range.

So revert it for now, we can re-visit this for 3.6. If we even need to:
as Minchan Kim says, "The patch wasn't a bug fix and even test workload
was very theoretical".

Reported-and-tested-by: Dave Jones <[e-mail]>
Acked-by: Hugh Dickins <[e-mail]>
Acked-by: KOSAKI Motohiro <[e-mail]>
Acked-by: Minchan Kim <[e-mail]>
Cc: Bartlomiej Zolnierkiewicz <[e-mail]>
Cc: Kyungmin Park <[e-mail]>
Cc: Andrew Morton <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

include/linux/compaction.h

···
 #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
···
 #define COMPACT_PARTIAL		2
 /* 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;

mm/compaction.c

···
 	 */
 	while (unlikely(too_many_isolated(zone))) {
 		/* async migration should just abort */
-		if (cc->mode != COMPACT_SYNC)
+		if (!cc->sync)
 			return 0;
 
 		congestion_wait(BLK_RW_ASYNC, HZ/10);
···
 		 * satisfies the allocation
 		 */
 		pageblock_nr = low_pfn >> pageblock_order;
-		if (cc->mode != COMPACT_SYNC &&
-		    last_pageblock_nr != pageblock_nr &&
+		if (!cc->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;
···
 			continue;
 		}
 
-		if (cc->mode != COMPACT_SYNC)
+		if (!cc->sync)
 			mode |= ISOLATE_ASYNC_MIGRATE;
 
 		lruvec = mem_cgroup_page_lruvec(page, zone);
···
 
 #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;
-}
-
-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)
+/* 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 FAIL_BAD_TARGET;
+		return false;
 
 	/* If the page is a large free page, then allow migration */
 	if (PageBuddy(page) && page_order(page) >= pageblock_order)
-		return GOOD_AS_MIGRATION_TARGET;
+		return true;
 
 	/* If the block is MIGRATE_MOVABLE or MIGRATE_CMA, allow migration */
-	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;
+	if (migrate_async_suitable(migratetype))
+		return true;
 
 	/* Otherwise skip the block */
-	return FAIL_BAD_TARGET;
+	return false;
 }
 
 /*
···
 	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
 	 * and free page scanners meet or enough free pages are isolated.
···
 	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;
···
 			continue;
 
 		/* Check the block is suitable for migration */
-		ret = suitable_migration_target(page, cc);
-		if (ret != GOOD_AS_MIGRATION_TARGET) {
-			if (ret == FAIL_UNMOVABLE_TARGET)
-				cc->nr_pageblocks_skipped++;
+		if (!suitable_migration_target(page))
 			continue;
-		}
+
 		/*
 		 * Found a block suitable for isolating free pages from. Now
 		 * we disabled interrupts, double check things are ok and
···
 		 */
 		isolated = 0;
 		spin_lock_irqsave(&zone->lock, flags);
-		ret = suitable_migration_target(page, cc);
-		if (ret == GOOD_AS_MIGRATION_TARGET) {
+		if (suitable_migration_target(page)) {
 			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);
 
 		/*
···
 
 		nr_migrate = cc->nr_migratepages;
 		err = migrate_pages(&cc->migratepages, compaction_alloc,
-			(unsigned long)&cc->freepages, false,
-			(cc->mode == COMPACT_SYNC) ? MIGRATE_SYNC_LIGHT
-						      : MIGRATE_ASYNC);
+				(unsigned long)cc, false,
+				cc->sync ? MIGRATE_SYNC_LIGHT : MIGRATE_ASYNC);
 		update_nr_listpages(cc);
 		nr_remaining = cc->nr_migratepages;
 
···
 
 static unsigned long compact_zone_order(struct zone *zone,
 				 int order, gfp_t gfp_mask,
-				 enum compact_mode mode,
-				 unsigned long *nr_pageblocks_skipped)
+				 bool sync)
 {
 	struct compact_control cc = {
 		.nr_freepages = 0,
···
 		.order = order,
 		.migratetype = allocflags_to_migratetype(gfp_mask),
 		.zone = zone,
-		.mode = mode,
+		.sync = sync,
 	};
-	unsigned long rc;
-
 	INIT_LIST_HEAD(&cc.freepages);
 	INIT_LIST_HEAD(&cc.migratepages);
 
-	rc = compact_zone(zone, &cc);
-	*nr_pageblocks_skipped = cc.nr_pageblocks_skipped;
-
-	return rc;
+	return compact_zone(zone, &cc);
 }
 
 int sysctl_extfrag_threshold = 500;
···
 	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
···
 								nodemask) {
 		int status;
 
-		mode = sync ? COMPACT_SYNC : COMPACT_ASYNC_MOVABLE;
-retry:
-		status = compact_zone_order(zone, order, gfp_mask, mode,
-						&nr_pageblocks_skipped);
+		status = compact_zone_order(zone, order, gfp_mask, sync);
 		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;
···
 			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->mode == COMPACT_SYNC)
+			else if (!ok && cc->sync)
 				defer_compaction(zone, cc->order);
 		}
 
···
 {
 	struct compact_control cc = {
 		.order = order,
-		.mode = COMPACT_ASYNC_MOVABLE,
+		.sync = false,
 	};
 
 	return __compact_pgdat(pgdat, &cc);
···
 {
 	struct compact_control cc = {
 		.order = -1,
-		.mode = COMPACT_SYNC,
+		.sync = true,
 	};
 
 	return __compact_pgdat(NODE_DATA(nid), &cc);

mm/internal.h

···
 /*
  * 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
···
 #endif
 
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
-#include <linux/compaction.h>
 
 /*
  * in mm/compaction.c
···
 	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 */
-	enum compact_mode mode;		/* Compaction mode */
+	bool sync;			/* Synchronous migration */
 
 	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

···
 
 int page_group_by_mobility_disabled __read_mostly;
 
-void set_pageblock_migratetype(struct page *page, int migratetype)
+static void set_pageblock_migratetype(struct page *page, int migratetype)
 {
 
 	if (unlikely(page_group_by_mobility_disabled))
···
 	return pages_moved;
 }
 
-int move_freepages_block(struct zone *zone, struct page *page,
-			 int migratetype)
+static int move_freepages_block(struct zone *zone, struct page *page,
+				int migratetype)
 {
 	unsigned long start_pfn, end_pfn;
 	struct page *start_page, *end_page;
···
 		.nr_migratepages = 0,
 		.order = -1,
 		.zone = page_zone(pfn_to_page(start)),
-		.mode = COMPACT_SYNC,
+		.sync = true,
 	};
 	INIT_LIST_HEAD(&cc.migratepages);