slab: remove one NR_CPUS dependency

Reduce high order allocations in do_tune_cpucache() for some setups.
(NR_CPUS=4096 -> we need 64KB)

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Christoph Lameter <cl@linux.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

mm/slab.c

@@ -3934,7 +3934,7 @@ fail:
 
 struct ccupdate_struct {
 	struct kmem_cache *cachep;
-	struct array_cache *new[NR_CPUS];
+	struct array_cache *new[0];
 };
 
 static void do_ccupdate_local(void *info)
@@ -3956,7 +3956,8 @@ static int do_tune_cpucache(struct kmem_cache *cachep, int limit,
 	struct ccupdate_struct *new;
 	int i;
 
-	new = kzalloc(sizeof(*new), gfp);
+	new = kzalloc(sizeof(*new) + nr_cpu_ids * sizeof(struct array_cache *),
+		      gfp);
 	if (!new)
 		return -ENOMEM;