Dont allocate pagesets for unpopulated zones.

We do not need to allocate pagesets for unpopulated zones.
This saves 1 mio pagesets per unpopulated zone on a 1k cpu / 1k node box.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.18-rc6-mm2/mm/page_alloc.c
===================================================================
--- linux-2.6.18-rc6-mm2.orig/mm/page_alloc.c	2006-09-18 14:14:58.000000000 -0500
+++ linux-2.6.18-rc6-mm2/mm/page_alloc.c	2006-09-18 14:54:43.456849813 -0500
@@ -1903,6 +1903,9 @@ static int __cpuinit process_zones(int c
 
 	for_each_zone(zone) {
 
+		if (!populated_zone(zone))
+			continue;
+
 		zone_pcp(zone, cpu) = kmalloc_node(sizeof(struct per_cpu_pageset),
 					 GFP_KERNEL, cpu_to_node(cpu));
 		if (!zone_pcp(zone, cpu))