From: Mel Gorman <mgorman@suse.de>
Date: Wed, 6 Aug 2014 23:07:18 +0000 (-0700)
Subject: mm: vmscan: only update per-cpu thresholds for online CPU
X-Git-Tag: v3.14.31~5
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=442ae03a52461e81eb95a776c9a3009fd4f7daca;p=thirdparty%2Fkernel%2Fstable.git

mm: vmscan: only update per-cpu thresholds for online CPU

commit bb0b6dffa2ccfbd9747ad0cc87c7459622896e60 upstream.

When kswapd is awake reclaiming, the per-cpu stat thresholds are lowered
to get more accurate counts to avoid breaching watermarks.  This
threshold update iterates over all possible CPUs which is unnecessary.
Only online CPUs need to be updated.  If a new CPU is onlined,
refresh_zone_stat_thresholds() will set the thresholds correctly.

Signed-off-by: Mel Gorman <mgorman@suse.de>
Acked-by: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Mel Gorman <mgorman@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 3034638eb4650..eded1909a6901 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -200,7 +200,7 @@ void set_pgdat_percpu_threshold(pg_data_t *pgdat,
 			continue;
 
 		threshold = (*calculate_pressure)(zone);
-		for_each_possible_cpu(cpu)
+		for_each_online_cpu(cpu)
 			per_cpu_ptr(zone->pageset, cpu)->stat_threshold
 							= threshold;
 	}