slub-use-raw_cpu_inc-for-incrementing-statistics-fix

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Cc: Christoph Lameter <cl@linux.com>
Cc: Fengguang Wu <fengguang.wu@intel.com>
Cc: Pekka Enberg <penberg@kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/slub.c

@@ -224,6 +224,10 @@ static inline void memcg_propagate_slab_attrs(struct kmem_cache *s) { }
 static inline void stat(const struct kmem_cache *s, enum stat_item si)
 {
 #ifdef CONFIG_SLUB_STATS
+	/*
+	 * The rmw is racy on a preemptible kernel but this is acceptable, so
+	 * avoid this_cpu_add()'s irq-disable overhead.
+	 */
 	raw_cpu_inc(s->cpu_slab->stat[si]);
 #endif
 }