[PATCH]compaction: checks correct fragmentation index

[PATCH]compaction: checks correct fragmentation index

[Shaohua Li]

fragmentation_index() returns -1000 when the allocation might succeed
This doesn't match the comment and code in compaction_suitable(). I
thought compaction_suitable should return COMPACT_PARTIAL in -1000
case, because in this case allocation could succeed depending on
watermarks.

Signed-off-by: Shaohua Li <shaohua.li@intel.com>

diff --git a/mm/compaction.c b/mm/compaction.c
index 021a296..59b0c4b 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -480,7 +480,8 @@ unsigned long compaction_suitable(struct zone *zone, int order)
 	 * fragmentation index determines if allocation failures are due to
 	 * low memory or external fragmentation
 	 *
-	 * index of -1 implies allocations might succeed dependingon watermarks
+	 * index of -1000 implies allocations might succeed depending on
+	 * watermarks
 	 * index towards 0 implies failure is due to lack of memory
 	 * index towards 1000 implies failure is due to fragmentation
 	 *
@@ -490,7 +491,8 @@ unsigned long compaction_suitable(struct zone *zone, int order)
 	if (fragindex >= 0 && fragindex <= sysctl_extfrag_threshold)
 		return COMPACT_SKIPPED;
 
-	if (fragindex == -1 && zone_watermark_ok(zone, order, watermark, 0, 0))
+	if (fragindex == -1000 && zone_watermark_ok(zone, order, watermark,
+	    0, 0))
 		return COMPACT_PARTIAL;
 
 	return COMPACT_CONTINUE;


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Re: [PATCH]compaction: checks correct fragmentation index

[Mel Gorman]

On Tue, Jun 07, 2011 at 04:36:41PM +0800, Shaohua Li wrote:
> fragmentation_index() returns -1000 when the allocation might succeed
> This doesn't match the comment and code in compaction_suitable(). I
> thought compaction_suitable should return COMPACT_PARTIAL in -1000
> case, because in this case allocation could succeed depending on
> watermarks.
> 
> Signed-off-by: Shaohua Li <shaohua.li@intel.com>

Well spotted. The impact of this is that compaction starts and
compact_finished() is called which rechecks the watermarks and the
free lists. It should have the same result in that compaction should
not start but is more expensive.

Acked-by: Mel Gorman <mel@csn.ul.ie>

-- 
Mel Gorman
SUSE Labs

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