Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758117AbXFAGAb (ORCPT ); Fri, 1 Jun 2007 02:00:31 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754831AbXFAGAV (ORCPT ); Fri, 1 Jun 2007 02:00:21 -0400 Received: from ns1.suse.de ([195.135.220.2]:58556 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754608AbXFAGAT (ORCPT ); Fri, 1 Jun 2007 02:00:19 -0400 From: Neil Brown To: David Chinner Date: Fri, 1 Jun 2007 15:59:51 +1000 MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Message-ID: <18015.46551.209946.204238@notabene.brown> Cc: Phillip Susi , Jens Axboe , david@lang.hm, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, dm-devel@redhat.com, linux-raid@vger.kernel.org, Stefan Bader , Andreas Dilger , Tejun Heo Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. In-Reply-To: message from David Chinner on Friday June 1 References: <20070528024559.GA85884050@sgi.com> <465C871F.708@cfl.rr.com> <20070529234832.GT85884050@sgi.com> <20070530061723.GY85884050@sgi.com> <20070531002011.GC85884050@sgi.com> <20070531062644.GI32105@kernel.dk> <20070531070307.GK85884050@sgi.com> <465F1479.70100@cfl.rr.com> <20070531233449.GT86004887@sgi.com> X-Mailer: VM 7.19 under Emacs 21.4.1 X-face: [Gw_3E*Gng}4rRrKRYotwlE?.2|**#s9D On Thu, May 31, 2007 at 02:31:21PM -0400, Phillip Susi wrote: > > David Chinner wrote: > > >That sounds like a good idea - we can leave the existing > > >WRITE_BARRIER behaviour unchanged and introduce a new WRITE_ORDERED > > >behaviour that only guarantees ordering. The filesystem can then > > >choose which to use where appropriate.... > > > > So what if you want a synchronous write, but DON'T care about the order? > > submit_bio(WRITE_SYNC, bio); > > Already there, already used by XFS, JFS and direct I/O. Are you sure? You seem to be saying that WRITE_SYNC causes the write to be safe on media before the request returns. That isn't my understanding. I think (from comments near the definition and a quick grep through the code) that WRITE_SYNC expedites the delivery of the request through the elevator, but doesn't do anything special about getting it onto the media. It essentially say "Submit this request now, don't wait for more request to bundle with it for better bandwidth utilisation" NeilBrown - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/