mm/z3fold.c: use xx_zalloc instead xx_alloc and memset

alloc_slots() allocates memory for slots using kmem_cache_alloc(), then
memsets it.  We can just use kmem_cache_zalloc().
Signed-off-by: Hui Su <sh_def@163.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Reviewed-by: NAndrew Morton <akpm@linux-foundation.org>
Link: https://lkml.kernel.org/r/20200926100834.GA184671@rlkSigned-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/z3fold.c

@@ -212,13 +212,12 @@ static inline struct z3fold_buddy_slots *alloc_slots(struct z3fold_pool *pool,
 {
 	struct z3fold_buddy_slots *slots;
 
-	slots = kmem_cache_alloc(pool->c_handle,
+	slots = kmem_cache_zalloc(pool->c_handle,
 				 (gfp & ~(__GFP_HIGHMEM | __GFP_MOVABLE)));
 
 	if (slots) {
 		/* It will be freed separately in free_handle(). */
 		kmemleak_not_leak(slots);
-		memset(slots->slot, 0, sizeof(slots->slot));
 		slots->pool = (unsigned long)pool;
 		rwlock_init(&slots->lock);
 	}