ext4: optimize ext4_ext_precache for 0 depth

This patch avoids the memory alloc & free path when depth is 0,
since anyway there is no extra caching done in that case.
So on checking depth 0, simply return early.
Signed-off-by: Ritesh Harjani <riteshh@linux.ibm.com>
Reviewed-by: Jan Kara <jack@suse.cz>
Link: https://lore.kernel.org/r/93da0d0f073c73358e85bb9849d8a5378d1da539.1582880246.git.riteshh@linux.ibm.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/extents.c

@@ -549,6 +549,12 @@ int ext4_ext_precache(struct inode *inode)
 	down_read(&ei->i_data_sem);
 	depth = ext_depth(inode);
 
+	/* Don't cache anything if there are no external extent blocks */
+	if (!depth) {
+		up_read(&ei->i_data_sem);
+		return ret;
+	}
+
 	path = kcalloc(depth + 1, sizeof(struct ext4_ext_path),
 		       GFP_NOFS);
 	if (path == NULL) {
@@ -556,9 +562,6 @@ int ext4_ext_precache(struct inode *inode)
 		return -ENOMEM;
 	}
 
-	/* Don't cache anything if there are no external extent blocks */
-	if (depth == 0)
-		goto out;
 	path[0].p_hdr = ext_inode_hdr(inode);
 	ret = ext4_ext_check(inode, path[0].p_hdr, depth, 0);
 	if (ret)