jbd2: use kmem_cache_zalloc for allocating journal head

This commit tries to use kmem_cache_zalloc instead of kmem_cache_alloc/
memset when a new journal head is alloctated.
Signed-off-by: NZheng Liu <wenqing.lz@taobao.com>
Cc: "Theodore Ts'o" <tytso@mit.edu>

fs/jbd2/journal.c

@@ -2325,13 +2325,13 @@ static struct journal_head *journal_alloc_journal_head(void)
 #ifdef CONFIG_JBD2_DEBUG
 	atomic_inc(&nr_journal_heads);
 #endif
-	ret = kmem_cache_alloc(jbd2_journal_head_cache, GFP_NOFS);
+	ret = kmem_cache_zalloc(jbd2_journal_head_cache, GFP_NOFS);
 	if (!ret) {
 		jbd_debug(1, "out of memory for journal_head\n");
 		pr_notice_ratelimited("ENOMEM in %s, retrying.\n", __func__);
 		while (!ret) {
 			yield();
-			ret = kmem_cache_alloc(jbd2_journal_head_cache, GFP_NOFS);
+			ret = kmem_cache_zalloc(jbd2_journal_head_cache, GFP_NOFS);
 		}
 	}
 	return ret;
@@ -2393,10 +2393,8 @@ struct journal_head *jbd2_journal_add_journal_head(struct buffer_head *bh)
 	struct journal_head *new_jh = NULL;
 
 repeat:
-	if (!buffer_jbd(bh)) {
+	if (!buffer_jbd(bh))
 		new_jh = journal_alloc_journal_head();
-		memset(new_jh, 0, sizeof(*new_jh));
-	}
 
 	jbd_lock_bh_journal_head(bh);
 	if (buffer_jbd(bh)) {