From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758939AbZBLQoL (ORCPT ); Thu, 12 Feb 2009 11:44:11 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1756983AbZBLQnx (ORCPT ); Thu, 12 Feb 2009 11:43:53 -0500 Received: from mx2.redhat.com ([66.187.237.31]:47319 "EHLO mx2.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756963AbZBLQnx (ORCPT ); Thu, 12 Feb 2009 11:43:53 -0500 Message-ID: <499451A0.3070403@redhat.com> Date: Thu, 12 Feb 2009 10:43:12 -0600 From: Eric Sandeen User-Agent: Thunderbird 2.0.0.19 (Macintosh/20081209) MIME-Version: 1.0 To: Jens Axboe CC: Jan Kara , Theodore Tso , =?ISO-8859-1?Q?Fernando_Luis_V=E1zquez_Cao?= , Alan Cox , Pavel Machek , kernel list Subject: Re: ext2 + -osync: not as easy as it seems References: <20090113131418.GD30352@atrey.karlin.mff.cuni.cz> <20090113134503.41318144@lxorguk.ukuu.org.uk> <20090113140347.GD17664@mit.edu> <20090113143011.GB10064@duck.suse.cz> <1231904239.11640.38.camel@sebastian.kern.oss.ntt.co.jp> <20090114103532.GA18834@duck.suse.cz> <20090114132146.GC6222@mit.edu> <20090114140532.GC19950@duck.suse.cz> <20090114140802.GC30821@kernel.dk> In-Reply-To: <20090114140802.GC30821@kernel.dk> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Jens Axboe wrote: > On Wed, Jan 14 2009, Jan Kara wrote: >>> I'm not sure what you mean; if the barrier operation isn't flushing >>> all of the caches all the way out to the iron oxide, it's not going to >>> be working properly no matter where it is being called, whether it's >>> in ext4_sync_file() or in jbd2's journal_submit_commit_record(). >> Well, I thought that a barrier, as an abstraction, only guarantees that >> any IO which happened before the barrier hits the iron before any IO which >> has been submitted after a barrier. This is actually enough for a >> journalling to work correctly but it's not enough for fsync() guarantees. >> But I might be wrong... > > It also guarentees that when you get a completion for that barrier > write, it's on safe storage. Think of it as a flush-write-flush > operation, in the presence of write back caching. (sorry for chiming in so late) Jens, isn't this just the way it's implemented today? At some point couldn't a barrier bio simply be a reordering barrier that the storage can use when destaging the write cache, rather than the heavy-handed flush-write-flush we have today? I guess it's a question of the intended semantics of a barrier bio, vs. today's implementation based on current hardware functionality... -Eric