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Date:	Tue,  7 Oct 2014 17:33:37 +0200
From:	Vlastimil Babka <>
To:	Andrew Morton <>
	Vlastimil Babka <>,
	Minchan Kim <>, Mel Gorman <>,
	Joonsoo Kim <>,
	Michal Nazarewicz <>,
	Naoya Horiguchi <>,
	Christoph Lameter <>,
	Rik van Riel <>,
	David Rientjes <>
Subject: [PATCH 3/5] mm, compaction: defer only on COMPACT_COMPLETE

Deferred compaction is employed to avoid compacting zone where sync direct
compaction has recently failed. As such, it makes sense to only defer when
a full zone was scanned, which is when compact_zone returns with
COMPACT_COMPLETE. It's less useful to defer when compact_zone returns with
apparent success (COMPACT_PARTIAL), followed by a watermark check failure,
which can happen due to parallel allocation activity. It also does not make
much sense to defer compaction which was completely skipped (COMPACT_SKIP) for
being unsuitable in the first place.

This patch therefore makes deferred compaction trigger only when
COMPACT_COMPLETE is returned from compact_zone(). Results of stress-highalloc
becnmark show the difference is within measurement error, so the issue is
rather cosmetic.

Signed-off-by: Vlastimil Babka <>
Cc: Minchan Kim <>
Cc: Mel Gorman <>
Cc: Joonsoo Kim <>
Cc: Michal Nazarewicz <>
Cc: Naoya Horiguchi <>
Cc: Christoph Lameter <>
Cc: Rik van Riel <>
Cc: David Rientjes <>
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 4b3e0bd..9107588 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1340,7 +1340,7 @@ unsigned long try_to_compact_pages(struct zonelist *zonelist,
 			goto break_loop;
-		if (mode != MIGRATE_ASYNC) {
+		if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) {
 			 * We think that allocation won't succeed in this zone
 			 * so we defer compaction there. If it ends up

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