slab: Make allocations with GFP_ZERO slightly more efficient

Use the likely mechanism already around valid
pointer tests to better choose when to memset
to 0 allocations with __GFP_ZERO

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

mm/slab.c

···
 	kmemleak_alloc_recursive(ptr, cachep->object_size, 1, cachep->flags,
 				 flags);
 
-	if (likely(ptr))
+	if (likely(ptr)) {
 		kmemcheck_slab_alloc(cachep, flags, ptr, cachep->object_size);
-
-	if (unlikely((flags & __GFP_ZERO) && ptr))
-		memset(ptr, 0, cachep->object_size);
+		if (unlikely(flags & __GFP_ZERO))
+			memset(ptr, 0, cachep->object_size);
+	}
 
 	return ptr;
 }
···
 				 flags);
 	prefetchw(objp);
 
-	if (likely(objp))
+	if (likely(objp)) {
 		kmemcheck_slab_alloc(cachep, flags, objp, cachep->object_size);
-
-	if (unlikely((flags & __GFP_ZERO) && objp))
-		memset(objp, 0, cachep->object_size);
+		if (unlikely(flags & __GFP_ZERO))
+			memset(objp, 0, cachep->object_size);
+	}
 
 	return objp;
 }