[PATCH 1/4] mm: compaction: Ensure rescanning only happens on partially scanned pageblocks

[Mel Gorman <mgorman@techsingularity.net>]

compact_zone() intends to rescan pageblocks if there is a failure to
migrate "within the current order-aligned block". However, the pageblock
scan may already be complete and moved to the next block causing the
next pageblock to be "rescanned". Ensure only the most recent pageblock
is rescanned.

Reported-by: Vlastimil Babka <vbabka@suse.cz>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/compaction.c | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index c8bcdea15f5f..81791c124bb8 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -2464,8 +2464,9 @@ compact_zone(struct compact_control *cc, struct capture_control *capc)
 			 * fast_find_migrateblock revisiting blocks that were
 			 * recently partially scanned.
 			 */
-			if (cc->direct_compaction && !cc->finish_pageblock &&
-						(cc->mode < MIGRATE_SYNC)) {
+			if (!pageblock_aligned(cc->migrate_pfn) &&
+			    cc->direct_compaction && !cc->finish_pageblock &&
+			    (cc->mode < MIGRATE_SYNC)) {
 				cc->finish_pageblock = true;
 
 				/*
-- 
2.35.3