From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Monakhov Subject: delalloc makes data=writeback safer Date: Wed, 09 Jun 2010 16:19:27 +0400 Message-ID: <877hm8jt4g.fsf@openvz.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii To: linux-ext4@vger.kernel.org Return-path: Received: from mail-fx0-f46.google.com ([209.85.161.46]:37661 "EHLO mail-fx0-f46.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751761Ab0FIMTb (ORCPT ); Wed, 9 Jun 2010 08:19:31 -0400 Received: by fxm8 with SMTP id 8so3531647fxm.19 for ; Wed, 09 Jun 2010 05:19:30 -0700 (PDT) Sender: linux-ext4-owner@vger.kernel.org List-ID: Everybody know that writeback mode for ext3 is potentially result in stale data in case of unclean umount. The same is true for ext4 with nodelalloc. But as far as i can see things is getting better in case of delalloc. In case of delalloc we have following calltrace: [writeback thread] ext4_da_writepages journal_start() ext4_map_blocks() -> real block allocation mpage_da_submit_io() -> submit_bh() -> submit_bio() journal_stop() So journal will be closed only after data was issued. And if journal->j_dev == journal->j_fs_dev (which is usually the case) data will be serialized with metadata. So it looks like it is impassible to see stale data even after unclean umount. Do I miss something? May be this was already discussed before, if so please post a link to previous discussion.