[PATCH] mm: vmscan: fix setting reclaim mode

[Hillf Danton]

The check for under memory pressure is corrected, then lumpy reclaim or
reclaim/compaction could be avoided either when for order-O reclaim or
when free pages are already low enough.


Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Mel Gorman <mgorman@xxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Hillf Danton <dhillf@xxxxxxxxx>
---

--- a/mm/vmscan.c	Thu Dec 29 20:20:16 2011
+++ b/mm/vmscan.c	Sun Jan  8 13:22:12 2012
@@ -365,8 +365,7 @@ out:
 	return ret;
 }

-static void set_reclaim_mode(int priority, struct scan_control *sc,
-				   bool sync)
+static void set_reclaim_mode(int priority, struct scan_control *sc, bool sync)
 {
 	reclaim_mode_t syncmode = sync ? RECLAIM_MODE_SYNC : RECLAIM_MODE_ASYNC;

@@ -381,13 +380,12 @@ static void set_reclaim_mode(int priorit
 		sc->reclaim_mode = RECLAIM_MODE_LUMPYRECLAIM;

 	/*
-	 * Avoid using lumpy reclaim or reclaim/compaction if possible by
-	 * restricting when its set to either costly allocations or when
-	 * under memory pressure
+	 * Avoid lumpy reclaim or reclaim/compaction either
+	 * when for order-O reclaim or when under memory pressure
 	 */
 	if (sc->order > PAGE_ALLOC_COSTLY_ORDER)
 		sc->reclaim_mode |= syncmode;
-	else if (sc->order && priority < DEF_PRIORITY - 2)
+	else if (sc->order && priority >= DEF_PRIORITY - 2)
 		sc->reclaim_mode |= syncmode;
 	else
 		sc->reclaim_mode = RECLAIM_MODE_SINGLE | RECLAIM_MODE_ASYNC;
--
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