slub: Add statistics for this_cmpxchg_double failures

Add some statistics for debugging.

Signed-off-by: Christoph Lameter <[e-mail]>
Signed-off-by: Pekka Enberg <[e-mail]>

include/linux/slub_def.h

···
 	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 {

mm/slub.c

···
 
 #endif
 
-static inline void stat(struct kmem_cache *s, enum stat_item si)
+static inline void stat(const struct kmem_cache *s, enum stat_item si)
 {
 #ifdef CONFIG_SLUB_STATS
 	__this_cpu_inc(s->cpu_slab->stat[si]);
···
 		printk("for unknown reason: actual=%lx was=%lx target=%lx\n",
 			actual_tid, tid, next_tid(tid));
 #endif
+	stat(s, CMPXCHG_DOUBLE_CPU_FAIL);
 }
 
 #endif