mm: compaction: prevent division-by-zero during user-requested compaction
authorJohannes Weiner <hannes@cmpxchg.org>
Thu, 20 Jan 2011 22:44:21 +0000 (14:44 -0800)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 21 Jan 2011 01:02:05 +0000 (17:02 -0800)
commit82478fb7bca28e3ca2f3c55c14e690f749dd4dbb
tree71023f480667dc3bfd255673437c76db77a05aa0
parent3305de51bf612603c9a4e4dc98ceb839ef933749
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 <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>
mm/compaction.c