ext4: remove unnecessary [cm]time update of quota file

It is not necessary to update [cm]time of quota file on each quota
file write and it wastes journal space and IO throughput with inode
writes. So just remove the updating from ext4_quota_write() and only
update times when quotas are being turned off. Userspace cannot get
anything reliable from quota files while they are used by the kernel
anyway.

Signed-off-by: Jan Kara <jack@suse.cz>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 22546ad..35ff9fe 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -4614,11 +4614,24 @@
 
 static int ext4_quota_off(struct super_block *sb, int type)
 {
+	struct inode *inode = sb_dqopt(sb)->files[type];
+	handle_t *handle;
+
 	/* Force all delayed allocation blocks to be allocated.
 	 * Caller already holds s_umount sem */
 	if (test_opt(sb, DELALLOC))
 		sync_filesystem(sb);
 
+	/* Update modification times of quota files when userspace can
+	 * start looking at them */
+	handle = ext4_journal_start(inode, 1);
+	if (IS_ERR(handle))
+		goto out;
+	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
+	ext4_mark_inode_dirty(handle, inode);
+	ext4_journal_stop(handle);
+
+out:
 	return dquot_quota_off(sb, type);
 }
 
@@ -4714,9 +4727,8 @@
 	if (inode->i_size < off + len) {
 		i_size_write(inode, off + len);
 		EXT4_I(inode)->i_disksize = inode->i_size;
+		ext4_mark_inode_dirty(handle, inode);
 	}
-	inode->i_mtime = inode->i_ctime = CURRENT_TIME;
-	ext4_mark_inode_dirty(handle, inode);
 	mutex_unlock(&inode->i_mutex);
 	return len;
 }