SLUB: Avoid touching per cpu array if kfree occurs to non cpu slab

We can avoid touching the per cpu array cacheline if the kfree
is not occurring to a per cpu slab.

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

Index: linux-2.6/mm/slub.c
===================================================================
--- linux-2.6.orig/mm/slub.c	2007-07-02 10:21:56.000000000 -0700
+++ linux-2.6/mm/slub.c	2007-07-02 10:24:53.000000000 -0700
@@ -1628,8 +1628,9 @@
 	unsigned long flags;
 
 	local_irq_save(flags);
-	if (likely(page == s->cpu_slab[smp_processor_id()] &&
-						!SlabDebug(page))) {
+	if (likely(SlabFrozen(page) &&
+			page == s->cpu_slab[smp_processor_id()] &&
+			!SlabDebug(page))) {
 		object[page->offset] = page->lockless_freelist;
 		page->lockless_freelist = object;
 	} else