vmstats: add cond_resched() to refresh_cpu_vm_stats()

We've found that it can take quite a bit of time (100's of usec) to get
through the zone loop in refresh_cpu_vm_stats().

Adding a cond_resched() to allow other threads to run in the non-preemptive
case.
Signed-off-by: Dimitri Sivanich <sivanich@sgi.com>
Acked-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmstat.c

@@ -322,6 +322,7 @@ void refresh_cpu_vm_stats(int cpu)
 				p->expire = 3;
 #endif
 			}
+		cond_resched();
 #ifdef CONFIG_NUMA
 		/*
 		 * Deal with draining the remote pageset of this