linux-kernel - [PATCH 2/3] mm, compaction: cover all compaction mode in compact

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Date:	Tue,  8 Mar 2016 14:42:44 +0100
From:	Michal Hocko <mhocko@...nel.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	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>,
	Hillf Danton <hillf.zj@...baba-inc.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Joonsoo Kim <js1304@...il.com>, <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.com>
Subject: [PATCH 2/3] mm, compaction: cover all compaction mode in compact_zone

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

the compiler is complaining after "mm, compaction: change COMPACT_
constants into enum"

mm/compaction.c: In function ‘compact_zone’:
mm/compaction.c:1350:2: warning: enumeration value ‘COMPACT_DEFERRED’ not handled in switch [-Wswitch]
  switch (ret) {
  ^
mm/compaction.c:1350:2: warning: enumeration value ‘COMPACT_COMPLETE’ not handled in switch [-Wswitch]
mm/compaction.c:1350:2: warning: enumeration value ‘COMPACT_NO_SUITABLE_PAGE’ not handled in switch [-Wswitch]
mm/compaction.c:1350:2: warning: enumeration value ‘COMPACT_NOT_SUITABLE_ZONE’ not handled in switch [-Wswitch]
mm/compaction.c:1350:2: warning: enumeration value ‘COMPACT_CONTENDED’ not handled in switch [-Wswitch]

compaction_suitable is allowed to return only COMPACT_PARTIAL,
COMPACT_SKIPPED and COMPACT_CONTINUE so other cases are simply
impossible. Put a VM_BUG_ON to catch an impossible return value.

Signed-off-by: Michal Hocko <mhocko@...e.com>
---
 mm/compaction.c | 13 +++++--------
 1 file changed, 5 insertions(+), 8 deletions(-)

diff --git a/mm/compaction.c b/mm/compaction.c
index 0f61f12d82b6..86968d3a04e6 100644
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -1347,15 +1347,12 @@ static enum compact_result compact_zone(struct zone *zone, struct compact_contro
 
 	ret = compaction_suitable(zone, cc->order, cc->alloc_flags,
 							cc->classzone_idx);
-	switch (ret) {
-	case COMPACT_PARTIAL:
-	case COMPACT_SKIPPED:
-		/* Compaction is likely to fail */
+	/* Compaction is likely to fail */
+	if (ret == COMPACT_PARTIAL || ret == COMPACT_SKIPPED)
 		return ret;
-	case COMPACT_CONTINUE:
-		/* Fall through to compaction */
-		;
-	}
+
+	/* huh, compaction_suitable is returning something unexpected */
+	VM_BUG_ON(ret != COMPACT_CONTINUE);
 
 	/*
 	 * Clear pageblock skip if there were failures recently and compaction
-- 
2.7.0