[PATCH 06/14] mm, compaction: Update compaction_result ordering

[Michal Hocko]

From: Michal Hocko <mhocko@xxxxxxxx>

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.

Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
---
 include/linux/compaction.h | 26 ++++++++++++++++----------
 1 file changed, 16 insertions(+), 10 deletions(-)

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
index 7c4de92d12cc..a7b9091ff349 100644
--- a/include/linux/compaction.h
+++ b/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
+	 * 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 */
-- 
2.8.0.rc3