From 82478fb7bca28e3ca2f3c55c14e690f749dd4dbb Mon Sep 17 00:00:00 2001
From: Johannes Weiner <hannes@cmpxchg.org>
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 <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 | 11 +++++++++++
1 file changed, 11 insertions(+)
diff --git a/mm/compaction.c b/mm/compaction.c
index 6d592a021072a8..8be430b812def9 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
--
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