From: Joonsoo Kim Date: Thu, 12 Feb 2015 22:59:50 +0000 (-0800) Subject: mm/compaction: fix wrong order check in compact_finished() X-Git-Tag: firefly_0821_release~176^2~2336^2~73 X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=372549c2a3778fd3df445819811c944ad54609ca;p=firefly-linux-kernel-4.4.55.git mm/compaction: fix wrong order check in compact_finished() 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 Acked-by: Vlastimil Babka Reviewed-by: Zhang Yanfei Cc: Mel Gorman Cc: David Rientjes Cc: Rik van Riel Cc: [3.7+] Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- diff --git a/mm/compaction.c b/mm/compaction.c index b68736c8a1ce..4954e196680c 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1173,7 +1173,7 @@ static int __compact_finished(struct zone *zone, struct compact_control *cc, 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; }