From 20311420282f3402888f1d9b8b80d924d491aadf Mon Sep 17 00:00:00 2001 From: Vlastimil Babka Date: Fri, 7 Oct 2016 17:00:46 -0700 Subject: [PATCH] mm, compaction: restrict fragindex to costly orders Fragmentation index and the vm.extfrag_threshold sysctl is meant as a heuristic to prevent excessive compaction for costly orders (i.e. THP). It's unlikely to make any difference for non-costly orders, especially with the default threshold. But we cannot afford any uncertainty for the non-costly orders where the only alternative to successful reclaim/compaction is OOM. After the recent patches we are guaranteed maximum effort without heuristics from compaction before deciding OOM, and fragindex is the last remaining heuristic. Therefore skip fragindex altogether for non-costly orders. Suggested-by: Michal Hocko Link: http://lkml.kernel.org/r/20160926162025.21555-5-vbabka@suse.cz Signed-off-by: Vlastimil Babka Acked-by: Michal Hocko Cc: Mel Gorman Cc: Joonsoo Kim Cc: David Rientjes Cc: Rik van Riel Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/mm/compaction.c b/mm/compaction.c index b918bdb28aed..0409a4ad6ea1 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -1435,9 +1435,14 @@ enum compact_result compaction_suitable(struct zone *zone, int order, * index towards 0 implies failure is due to lack of memory * index towards 1000 implies failure is due to fragmentation * - * Only compact if a failure would be due to fragmentation. + * Only compact if a failure would be due to fragmentation. Also + * ignore fragindex for non-costly orders where the alternative to + * a successful reclaim/compaction is OOM. Fragindex and the + * vm.extfrag_threshold sysctl is meant as a heuristic to prevent + * excessive compaction for costly orders, but it should not be at the + * expense of system stability. */ - if (ret == COMPACT_CONTINUE) { + if (ret == COMPACT_CONTINUE && (order > PAGE_ALLOC_COSTLY_ORDER)) { fragindex = fragmentation_index(zone, order); if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold) ret = COMPACT_NOT_SUITABLE_ZONE; -- 2.20.1