From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Stefan Bader" Subject: Re: [RFD] BIO_RW_BARRIER - what it means for devices, filesystems, and dm/md. Date: Wed, 30 May 2007 10:55:13 +0200 Message-ID: <5201e28f0705300155ue7ce985m3f318ff7ff1a1396@mail.gmail.com> References: <18006.38689.818186.221707@notabene.brown> <18010.12472.209452.148229@notabene.brown> <20070528024559.GA85884050@sgi.com> <465C871F.708@cfl.rr.com> <20070529234832.GT85884050@sgi.com> <20070530061723.GY85884050@sgi.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20070530061723.GY85884050@sgi.com> Content-Disposition: inline List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: David Chinner Cc: david@lang.hm, Tejun Heo , linux-kernel@vger.kernel.org, linux-raid@vger.kernel.org, dm-devel@redhat.com, Jens Axboe , linux-fsdevel@vger.kernel.org, Andreas Dilger List-Id: linux-raid.ids > The order that these are expected by the filesystem to hit stable > storage are: > > 1. block 4 and 10 on stable storage in any order > 2. barrier block X on stable storage > 3. block 5 and 20 on stable storage in any order > > The point I'm trying to make is that in XFS, block 5 and 20 cannot > be allowed to hit the disk before the barrier block because they > have strict order dependency on block X being stable before them, > just like block X has strict order dependency that block 4 and 10 > must be stable before we start the barrier block write. > That would be the exactly how I understand Documentation/block/barrier.txt: "In other words, I/O barrier requests have the following two properties. 1. Request ordering ... 2. Forced flushing to physical medium" "So, I/O barriers need to guarantee that requests actually get written to non-volatile medium in order." Stefan