mm/z3fold: remove magic number in z3fold_create_pool()

It's meaningless to pass a magic number 2 to __alloc_percpu() as there is
a minimum alignment size of PCPU_MIN_ALLOC_SIZE (> 2) in it.  Also there
is no special alignment requirement for unbuddied.  So we could replace
this magic number with nature alignment, i.e.  __alignof__(struct
list_head), to improve readability.

Link: https://lkml.kernel.org/r/20210619093151.1492174-4-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Vitaly Wool <vitaly.wool@konsulko.com>
Cc: Hillf Danton <hdanton@sina.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/z3fold.c

@@ -998,7 +998,8 @@ static struct z3fold_pool *z3fold_create_pool(const char *name, gfp_t gfp,
 		goto out_c;
 	spin_lock_init(&pool->lock);
 	spin_lock_init(&pool->stale_lock);
-	pool->unbuddied = __alloc_percpu(sizeof(struct list_head)*NCHUNKS, 2);
+	pool->unbuddied = __alloc_percpu(sizeof(struct list_head) * NCHUNKS,
+					 __alignof__(struct list_head));
 	if (!pool->unbuddied)
 		goto out_pool;
 	for_each_possible_cpu(cpu) {