[PATCH] mm: do not check unpopulated zones for draining and counter updates

If a zone is unpopulated then we do not need to check for pages that are to
be drained and also not for vm counters that may need to be updated.

Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

mm/vmstat.c

@@ -321,6 +321,9 @@ void refresh_cpu_vm_stats(int cpu)
 	for_each_zone(zone) {
 		struct per_cpu_pageset *pcp;
 
+		if (!populated_zone(zone))
+			continue;
+
 		pcp = zone_pcp(zone, cpu);
 
 		for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++)