linux-kernel - [PATCH 04/14] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT

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Date:	Wed, 20 Apr 2016 15:47:17 -0400
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Johannes Weiner <hannes@...xchg.org>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Tetsuo Handa <penguin-kernel@...ove.SAKURA.ne.jp>,
	Joonsoo Kim <js1304@...il.com>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	Vlastimil Babka <vbabka@...e.cz>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 04/14] mm, compaction: distinguish COMPACT_DEFERRED from COMPACT_SKIPPED

From: Michal Hocko <mhocko@...e.com>

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.

Acked-by: Vlastimil Babka <vbabka@...e.cz>
Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 include/linux/compaction.h        | 7 +++++--
 include/trace/events/compaction.h | 2 +-
 mm/compaction.c                   | 8 +++++---
 3 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index 4458fd94170f..7e177d111c39 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -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,
 	/*
diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index e215bf68f521..6ba16c86d7db 100644
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -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")		\
diff --git a/mm/compaction.c b/mm/compaction.c
index b06de27b7f72..13709e33a2fc 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1637,7 +1637,7 @@ 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;
@@ -1654,8 +1654,10 @@ 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,
@@ -1726,7 +1728,7 @@ 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;
-- 
2.8.0.rc3