[Devel] [PATCH rh7 24/25] ms/mm/compaction: fix wrong order check in compact_finished()

[Andrey Ryabinin]

From: Joonsoo Kim <iamjoonsoo.kim at lge.com>

What we want to check here is whether there is highorder freepage in buddy
list of other migratetype in order to steal it without fragmentation.
But, current code just checks cc->order which means allocation request
order.  So, this is wrong.

Without this fix, non-movable synchronous compaction below pageblock order
would not stopped until compaction is complete, because migratetype of
most pageblocks are movable and high order freepage made by compaction is
usually on movable type buddy list.

There is some report related to this bug. See below link.

  http://www.spinics.net/lists/linux-mm/msg81666.html

Although the issued system still has load spike comes from compaction,
this makes that system completely stable and responsive according to his
report.

stress-highalloc test in mmtests with non movable order 7 allocation
doesn't show any notable difference in allocation success rate, but, it
shows more compaction success rate.

Compaction success rate (Compaction success * 100 / Compaction stalls, %)
18.47 : 28.94

Fixes: 1fb3f8ca0e92 ("mm: compaction: capture a suitable high-order page immediately when it is made available")
Signed-off-by: Joonsoo Kim <iamjoonsoo.kim at lge.com>
Acked-by: Vlastimil Babka <vbabka at suse.cz>
Reviewed-by: Zhang Yanfei <zhangyanfei at cn.fujitsu.com>
Cc: Mel Gorman <mgorman at suse.de>
Cc: David Rientjes <rientjes at google.com>
Cc: Rik van Riel <riel at redhat.com>
Cc: <stable at vger.kernel.org>	[3.7+]
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit 372549c2a3778fd3df445819811c944ad54609ca)
Signed-off-by: Andrey Ryabinin <aryabinin at virtuozzo.com>
---
 mm/compaction.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 4f6d23a87230..995097d8c50a 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -941,7 +941,7 @@ static int compact_finished(struct zone *zone,
 			return COMPACT_PARTIAL;
 
 		/* Job done if allocation would set block type */
-		if (cc->order >= pageblock_order && area->nr_free)
+		if (order >= pageblock_order && area->nr_free)
 			return COMPACT_PARTIAL;
 	}
 
-- 
2.13.6