From: Andreas Dilger Subject: Re: [PATCH 0/4] (RESEND) ext3[34] barrier changes Date: Sat, 17 May 2008 11:59:58 -0600 Message-ID: <20080517175958.GL3491@webber.adilger.int> References: <482DDA56.6000301@redhat.com> <20080516130545.845a3be9.akpm@linux-foundation.org> <482DF44B.50204@redhat.com> <20080516220315.GB15334@shareable.org> <482E08E6.4030507@redhat.com> <20080516225304.GG15334@shareable.org> <20080517002030.GA7374@mit.edu> <20080516173552.e88183d9.akpm@linux-foundation.org> <20080517134344.GA7411@mit.edu> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7BIT To: Theodore Tso , Andrew Morton , Eric Sandeen , linux-ext4@vger.kernel.org, linux-kernel@vger.kernel.org, linux-fsdevel@vge Return-path: Received: from sca-es-mail-1.Sun.COM ([192.18.43.132]:54412 "EHLO sca-es-mail-1.sun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752868AbYEQSAJ (ORCPT ); Sat, 17 May 2008 14:00:09 -0400 In-reply-to: <20080517134344.GA7411@mit.edu> Content-disposition: inline Sender: linux-ext4-owner@vger.kernel.org List-ID: On May 17, 2008 09:43 -0400, Theodore Ts'o wrote: > On Fri, May 16, 2008 at 05:35:52PM -0700, Andrew Morton wrote: > > Journal wrapping could cause the commit block to get written before its > > data blocks. We could improve that by changing the journal layout a bit: > > wrap the entire commit rather than just its tail. Such a change might > > be intrusive though. > > Or we backport jbd2's checksum support in the commit block to jbd; > with the checksum support, if the commit block is written out-of-order > with the rest of the blocks in the commit, the commit will simply not > be recognized as valid, and we'll use the previous commit block as the > last valid commit. The jbd2 journal checksum support, along with the 64-bit journal block layout is designed to be 100% compatible with jbd, so it would be trivial to "back port" jbd2. Just copy jbd2 into jbd, and add the option to set (or set by default) the JBD_FEATURE_COMPAT_CHECKSUM feature in the journal. I was going to suggest complete removal of jbd2 at that point, but the ordered-mode rewrite is still pending and should live in ext4 for a reasonably long while before going back to ext3. Cheers, Andreas -- Andreas Dilger Sr. Staff Engineer, Lustre Group Sun Microsystems of Canada, Inc.