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 <[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]>

Author: Michal Hocko

include/linux/compaction.h

@@ -4,37 +4,43 @@
 /* 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
 	 */
 	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
+	 * The full zone was compacted scanned but wasn't successfull to compact
+	 * suitable pages.
 	 */
-	COMPACT_PARTIAL,
+	COMPACT_COMPLETE,
 	/*
 	 * 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,
+
 	/*
-	 * The full zone was compacted scanned but wasn't successfull to compact
-	 * suitable pages.
+	 * direct compaction partially compacted a zone and there might be
+	 * suitable pages
 	 */
-	COMPACT_COMPLETE,
-	/* For more detailed tracepoint output */
-	COMPACT_NO_SUITABLE_PAGE,
-	COMPACT_NOT_SUITABLE_ZONE,
-	COMPACT_CONTENDED,
+	COMPACT_PARTIAL,
 };
 
 /* Used to signal whether compaction detected need_sched() or lock contention */