slub: Add statistics for this_cmpxchg_double failures

Add some statistics for debugging.

Signed-off-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>
diff --git a/include/linux/slub_def.h b/include/linux/slub_def.h
index 90fbb6d..45ca123 100644
--- a/include/linux/slub_def.h
+++ b/include/linux/slub_def.h
@@ -32,6 +32,7 @@
 	DEACTIVATE_TO_TAIL,	/* Cpu slab was moved to the tail of partials */
 	DEACTIVATE_REMOTE_FREES,/* Slab contained remotely freed objects */
 	ORDER_FALLBACK,		/* Number of times fallback was necessary */
+	CMPXCHG_DOUBLE_CPU_FAIL,/* Failure of this_cpu_cmpxchg_double */
 	NR_SLUB_STAT_ITEMS };
 
 struct kmem_cache_cpu {