From 82478fb7bca28e3ca2f3c55c14e690f749dd4dbb Mon Sep 17 00:00:00 2001 From: Johannes Weiner Date: Thu, 20 Jan 2011 14:44:21 -0800 Subject: [PATCH] mm: compaction: prevent division-by-zero during user-requested compaction Up until 3e7d344 ("mm: vmscan: reclaim order-0 and use compaction instead of lumpy reclaim"), compaction skipped calculating the fragmentation index of a zone when compaction was explicitely requested through the procfs knob. However, when compaction_suitable was introduced, it did not come with an extra check for order == -1, set on explicit compaction requests, and passed this order on to the fragmentation index calculation, where it overshifts the number of requested pages, leading to a division by zero. This patch makes sure that order == -1 is recognized as the flag it is rather than passing it along as valid order parameter. [akpm@linux-foundation.org: add comment, per Mel] Signed-off-by: Johannes Weiner Reviewed-by: Mel Gorman Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/compaction.c | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/mm/compaction.c b/mm/compaction.c index 6d592a021072..8be430b812de 100644 --- a/mm/compaction.c +++ b/mm/compaction.c @@ -406,6 +406,10 @@ static int compact_finished(struct zone *zone, if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0)) return COMPACT_CONTINUE; + /* + * order == -1 is expected when compacting via + * /proc/sys/vm/compact_memory + */ if (cc->order == -1) return COMPACT_CONTINUE; @@ -453,6 +457,13 @@ unsigned long compaction_suitable(struct zone *zone, int order) if (!zone_watermark_ok(zone, 0, watermark, 0, 0)) return COMPACT_SKIPPED; + /* + * order == -1 is expected when compacting via + * /proc/sys/vm/compact_memory + */ + if (order == -1) + return COMPACT_CONTINUE; + /* * fragmentation index determines if allocation failures are due to * low memory or external fragmentation