Commit 82478fb7 authored Jan 20, 2011 by Johannes Weiner Committed by Linus Torvalds Jan 20, 2011

mm: compaction: prevent division-by-zero during user-requested compaction



Up until 3e7d3449 ("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 <hannes@cmpxchg.org>
Reviewed-by: Mel Gorman <mel@csn.ul.ie>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 3305de51

mm/compaction.c

+11 −0

Original line number	Original line	Diff line number	Diff line
	@@ -406,6 +406,10 @@ static int compact_finished(struct zone *zone,
	if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))		if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
	return COMPACT_CONTINUE;		return COMPACT_CONTINUE;

			/*
			* order == -1 is expected when compacting via
			* /proc/sys/vm/compact_memory
			*/
	if (cc->order == -1)		if (cc->order == -1)
	return COMPACT_CONTINUE;		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))		if (!zone_watermark_ok(zone, 0, watermark, 0, 0))
	return COMPACT_SKIPPED;		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		* fragmentation index determines if allocation failures are due to
	* low memory or external fragmentation		* low memory or external fragmentation