[Xenial PATCH 05/11] mm, compaction: distinguish between full and partial COMPACT_COMPLETE

[Thadeu Lima de Souza Cascardo]

From: Michal Hocko <mhocko at suse.com>

BugLink: https://bugs.launchpad.net/bugs/1655842

COMPACT_COMPLETE now means that compaction and free scanner met.  This
is not very useful information if somebody just wants to use this
feedback and make any decisions based on that.  The current caller might
be a poor guy who just happened to scan tiny portion of the zone and
that could be the reason no suitable pages were compacted.  Make sure we
distinguish the full and partial zone walks.

Consumers should treat COMPACT_PARTIAL_SKIPPED as a potential success
and be optimistic in retrying.

The existing users of COMPACT_COMPLETE are conservatively changed to use
COMPACT_PARTIAL_SKIPPED as well but some of them should be probably
reconsidered and only defer the compaction only for COMPACT_COMPLETE
with the new semantic.

This patch shouldn't introduce any functional changes.

Signed-off-by: Michal Hocko <mhocko at suse.com>
Acked-by: Vlastimil Babka <vbabka at suse.cz>
Acked-by: Hillf Danton <hillf.zj at alibaba-inc.com>
Cc: David Rientjes <rientjes at google.com>
Cc: Johannes Weiner <hannes at cmpxchg.org>
Cc: Joonsoo Kim <js1304 at gmail.com>
Cc: Mel Gorman <mgorman at techsingularity.net>
Cc: Tetsuo Handa <penguin-kernel at I-love.SAKURA.ne.jp>
Cc: Vladimir Davydov <vdavydov at virtuozzo.com>
Signed-off-by: Andrew Morton <akpm at linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds at linux-foundation.org>
(cherry picked from commit c8f7de0bfae36e8532e5e25a39d15407f02aca78)
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo at canonical.com>
---
 include/linux/compaction.h        | 10 +++++++++-
 include/trace/events/compaction.h |  1 +
 mm/compaction.c                   | 12 ++++++++++--
 mm/internal.h                     |  1 +
 4 files changed, 21 insertions(+), 3 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index 78eeaf6..ca262db 100644
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -21,7 +21,15 @@ enum compact_result {
 	 * pages
 	 */
 	COMPACT_PARTIAL,
-	/* The full zone was compacted */
+	/*
+	 * direct compaction has scanned part of the zone but wasn't successfull
+	 * to compact suitable pages.
+	 */
+	COMPACT_PARTIAL_SKIPPED,
+	/*
+	 * The full zone was compacted scanned but wasn't successfull to compact
+	 * suitable pages.
+	 */
 	COMPACT_COMPLETE,
 	/* For more detailed tracepoint output */
 	COMPACT_NO_SUITABLE_PAGE,
diff --git a/include/trace/events/compaction.h b/include/trace/events/compaction.h
index ace0a02..b75be5c 100644
--- a/include/trace/events/compaction.h
+++ b/include/trace/events/compaction.h
@@ -14,6 +14,7 @@
 	EM( COMPACT_DEFERRED,		"deferred")		\
 	EM( COMPACT_CONTINUE,		"continue")		\
 	EM( COMPACT_PARTIAL,		"partial")		\
+	EM( COMPACT_PARTIAL_SKIPPED,	"partial_skipped")	\
 	EM( COMPACT_COMPLETE,		"complete")		\
 	EM( COMPACT_NO_SUITABLE_PAGE,	"no_suitable_page")	\
 	EM( COMPACT_NOT_SUITABLE_ZONE,	"not_suitable_zone")	\
diff --git a/mm/compaction.c b/mm/compaction.c
index 2ee037d..3a4ec9f 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1205,7 +1205,10 @@ static enum compact_result __compact_finished(struct zone *zone, struct compact_
 		if (!current_is_kswapd())
 			zone->compact_blockskip_flush = true;
 
-		return COMPACT_COMPLETE;
+		if (cc->whole_zone)
+			return COMPACT_COMPLETE;
+		else
+			return COMPACT_PARTIAL_SKIPPED;
 	}
 
 	if (is_via_compact_memory(cc->order))
@@ -1370,6 +1373,10 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
 		zone->compact_cached_migrate_pfn[0] = cc->migrate_pfn;
 		zone->compact_cached_migrate_pfn[1] = cc->migrate_pfn;
 	}
+
+	if (cc->migrate_pfn == start_pfn)
+		cc->whole_zone = true;
+
 	cc->last_migrated_pfn = 0;
 
 	trace_mm_compaction_begin(start_pfn, cc->migrate_pfn,
@@ -1578,7 +1585,8 @@ enum compact_result try_to_compact_pages(gfp_t gfp_mask, unsigned int order,
 			goto break_loop;
 		}
 
-		if (mode != MIGRATE_ASYNC && status == COMPACT_COMPLETE) {
+		if (mode != MIGRATE_ASYNC && (status == COMPACT_COMPLETE ||
+					status == COMPACT_PARTIAL_SKIPPED)) {
 			/*
 			 * We think that allocation won't succeed in this zone
 			 * so we defer compaction there. If it ends up
diff --git a/mm/internal.h b/mm/internal.h
index 066f3cb..fee09cd 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -206,6 +206,7 @@ struct compact_control {
 	unsigned long last_migrated_pfn;/* Not yet flushed page being freed */
 	enum migrate_mode mode;		/* Async or sync migration mode */
 	bool ignore_skip_hint;		/* Scan blocks even if marked skip */
+	bool whole_zone;		/* Whole zone has been scanned */
 	int order;			/* order a direct compactor needs */
 	const gfp_t gfp_mask;		/* gfp mask of a direct compactor */
 	const unsigned int alloc_flags;	/* alloc flags of a direct compactor */
-- 
2.9.3