56de7263 (mm: compaction: direct compact when a high-order allocation
fails) introduced a check for cc->order == -1 in compact_finished. We
should continue compacting in that case because the request came from
userspace and there is no particular order to compact for.
The check is, however, done after zone_watermark_ok which uses order as
a right hand argument for shifts. Not only watermark check is pointless
if we can break out without it but it also uses 1 << -1 which is not
well defined (at least from C standard). Let's move the -1 check above
zone_watermark_ok.
Signed-off-by: Michal Hocko <mhocko@xxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
---
compaction.c | 14 +++++++-------
1 file changed, 7 insertions(+), 7 deletions(-)
Index: linus_tree/mm/compaction.c
===================================================================
--- linus_tree.orig/mm/compaction.c 2011-05-30 14:19:58.000000000 +0200
+++ linus_tree/mm/compaction.c 2011-05-30 14:20:40.000000000 +0200
@@ -420,13 +420,6 @@ static int compact_finished(struct zone
if (cc->free_pfn <= cc->migrate_pfn)
return COMPACT_COMPLETE;
- /* Compaction run is not finished if the watermark is not met */
- watermark = low_wmark_pages(zone);
- watermark += (1 << cc->order);
-
- 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
@@ -434,6 +427,13 @@ static int compact_finished(struct zone
if (cc->order == -1)
return COMPACT_CONTINUE;
+ /* Compaction run is not finished if the watermark is not met */
+ watermark = low_wmark_pages(zone);
+ watermark += (1 << cc->order);
+
+ if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
+ return COMPACT_CONTINUE;
+
/* Direct compactor: Is a suitable page free? */
for (order = cc->order; order < MAX_ORDER; order++) {
/* Job done if page is free of the right migratetype */
--
Michal Hocko
SUSE Labs
SUSE LINUX s.r.o.
Lihovarska 1060/12
190 00 Praha 9
Czech Republic
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