mm, slab_common: add 'unlikely' to size check of kmalloc_slab()

Size is usually below than KMALLOC_MAX_SIZE.
If we add a 'unlikely' macro, compiler can make better code.
Acked-by: NChristoph Lameter <cl@linux.com>
Signed-off-by: NJoonsoo Kim <iamjoonsoo.kim@lge.com>
Signed-off-by: NPekka Enberg <penberg@kernel.org>

mm/slab_common.c

@@ -373,7 +373,7 @@ struct kmem_cache *kmalloc_slab(size_t size, gfp_t flags)
 {
 	int index;
 
-	if (size > KMALLOC_MAX_SIZE) {
+	if (unlikely(size > KMALLOC_MAX_SIZE)) {
 		WARN_ON_ONCE(!(flags & __GFP_NOWARN));
 		return NULL;
 	}