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mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED

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try_to_compact_pages() can currently return COMPACT_SKIPPED even when
the compaction is defered for some zone just because zone DMA is skipped
in 99% of cases due to watermark checks.  This makes COMPACT_DEFERRED
basically unusable for the page allocator as a feedback mechanism.

Make sure we distinguish those two states properly and switch their
ordering in the enum.  This would mean that the COMPACT_SKIPPED will be
returned only when all eligible zones are skipped.

As a result COMPACT_DEFERRED handling for THP in __alloc_pages_slowpath
will be more precise and we would bail out rather than reclaim.

Signed-off-by: Michal Hocko <[email protected]>
Acked-by: Vlastimil Babka <[email protected]>
Acked-by: Hillf Danton <[email protected]>
Cc: David Rientjes <[email protected]>
Cc: Johannes Weiner <[email protected]>
Cc: Joonsoo Kim <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: Tetsuo Handa <[email protected]>
Cc: Vladimir Davydov <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Michal Hocko 2016-05-20 16:56:44 -07:00 • committed by Linus Torvalds
commit 1d4746d395
3 changed files with 11 additions and 6 deletions
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8
mm/compaction.c
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@ -1578,7 +1578,7 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
int may_perform_io = gfp_mask & __GFP_IO;
struct zoneref *z;
struct zone *zone;
enum compact_result rc = COMPACT_DEFERRED;
enum compact_result rc = COMPACT_SKIPPED;
int all_zones_contended = COMPACT_CONTENDED_LOCK; /* init for &= op */
*contended = COMPACT_CONTENDED_NONE;
@ -1595,8 +1595,10 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
enum compact_result status;
int zone_contended;
if (compaction_deferred(zone, order))
if (compaction_deferred(zone, order)) {
rc = max_t(enum compact_result, COMPACT_DEFERRED, rc);
continue;
}
status = compact_zone_order(zone, order, gfp_mask, mode,
&zone_contended, alloc_flags,
@ -1667,7 +1669,7 @@ break_loop:
* If at least one zone wasn't deferred or skipped, we report if all
* zones that were tried were lock contended.
*/
if (rc > COMPACT_SKIPPED && all_zones_contended)
if (rc > COMPACT_INACTIVE && all_zones_contended)
*contended = COMPACT_CONTENDED_LOCK;
return rc;