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Commit 1d4746d3 authored by Michal Hocko's avatar Michal Hocko Committed by Linus Torvalds
Browse files

mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED 



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: default avatarMichal Hocko <mhocko@suse.com>
Acked-by: default avatarVlastimil Babka <vbabka@suse.cz>
Acked-by: default avatarHillf Danton <hillf.zj@alibaba-inc.com>
Cc: David Rientjes <rientjes@google.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Mel Gorman <mgorman@techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel@I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov@virtuozzo.com>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent c46649de

include/linux/compaction.h

+5 −2
Original line number Diff line number Diff line
@@ -4,13 +4,16 @@ 
/* Return values for compact_zone() and try_to_compact_pages() */

/* When adding new states, please adjust include/trace/events/compaction.h */

enum compact_result {

	/* compaction didn't start as it was deferred due to past failures */

	COMPACT_DEFERRED,

	/*

	 * compaction didn't start as it was not possible or direct reclaim

	 * was more suitable

	 */

	COMPACT_SKIPPED,

	/* compaction didn't start as it was deferred due to past failures */

	COMPACT_DEFERRED,

	/* compaction not active last round */

	COMPACT_INACTIVE = COMPACT_DEFERRED,



	/* compaction should continue to another pageblock */

	COMPACT_CONTINUE,

	/*

include/trace/events/compaction.h

+1 −1
Original line number Diff line number Diff line
@@ -10,8 +10,8 @@ 
#include <trace/events/mmflags.h>



#define COMPACTION_STATUS					\

	EM( COMPACT_DEFERRED,		"deferred")		\

	EM( COMPACT_SKIPPED,		"skipped")		\

	EM( COMPACT_DEFERRED,		"deferred")		\

	EM( COMPACT_CONTINUE,		"continue")		\

	EM( COMPACT_PARTIAL,		"partial")		\

	EM( COMPACT_COMPLETE,		"complete")		\

mm/compaction.c

+5 −3
Original line number Diff line number Diff line
@@ -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 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order, 
	 * 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;