mm, compaction: update compaction_result ordering

compaction_result will be used as the primary feedback channel for
compaction users.  At the same time try_to_compact_pages (and
potentially others) assume a certain ordering where a more specific
feedback takes precendence.

This gets a bit awkward when we have conflicting feedback from different
zones.  E.g one returing COMPACT_COMPLETE meaning the full zone has been
scanned without any outcome while other returns with COMPACT_PARTIAL aka
made some progress.  The caller should get COMPACT_PARTIAL because that
means that the compaction still can make some progress.  The same
applies for COMPACT_PARTIAL vs COMPACT_PARTIAL_SKIPPED.

Reorder PARTIAL to be the largest one so the larger the value is the
more progress we have done.

Signed-off-by: Michal Hocko <mhocko@suse.com>
Acked-by: Vlastimil Babka <vbabka@suse.cz>
Acked-by: Hillf 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: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/compaction.h

@@ -4,6 +4,8 @@
 /* Return values for compact_zone() and try_to_compact_pages() */
 /* When adding new states, please adjust include/trace/events/compaction.h */
 enum compact_result {
+	/* For more detailed tracepoint output - internal to compaction */
+	COMPACT_NOT_SUITABLE_ZONE,
 	/*
 	 * compaction didn't start as it was not possible or direct reclaim
 	 * was more suitable
@@ -11,30 +13,34 @@ enum compact_result {
 	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,
 
+	/* For more detailed tracepoint output - internal to compaction */
+	COMPACT_NO_SUITABLE_PAGE,
 	/* compaction should continue to another pageblock */
 	COMPACT_CONTINUE,
-	/*
-	 * direct compaction partially compacted a zone and there are suitable
-	 * pages
-	 */
-	COMPACT_PARTIAL,
-	/*
-	 * 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,
-	COMPACT_NOT_SUITABLE_ZONE,
+	/*
+	 * direct compaction has scanned part of the zone but wasn't successfull
+	 * to compact suitable pages.
+	 */
+	COMPACT_PARTIAL_SKIPPED,
+
+	/* compaction terminated prematurely due to lock contentions */
 	COMPACT_CONTENDED,
+
+	/*
+	 * direct compaction partially compacted a zone and there might be
+	 * suitable pages
+	 */
+	COMPACT_PARTIAL,
 };
 
 /* Used to signal whether compaction detected need_sched() or lock contention */