From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id p0CCi1jd190844 for ; Wed, 12 Jan 2011 06:44:01 -0600 Received: from mail.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id 955B325DDBD for ; Wed, 12 Jan 2011 04:46:13 -0800 (PST) Received: from mail.internode.on.net (bld-mail14.adl6.internode.on.net [150.101.137.99]) by cuda.sgi.com with ESMTP id qDyf0EuUBznz1u2i for ; Wed, 12 Jan 2011 04:46:13 -0800 (PST) Date: Wed, 12 Jan 2011 23:44:31 +1100 From: Dave Chinner Subject: Re: [PATCH 1/6] fs: add hole punching to fallocate Message-ID: <20110112124431.GP28803@dastard> References: <1289248327-16308-1-git-send-email-josef@redhat.com> <20101109011222.GD2715@dastard> <20101109033038.GF3099@thunk.org> <20101109044242.GH2715@dastard> <20101109214147.GK3099@thunk.org> <20101109234049.GQ2715@dastard> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Lawrence Greenfield Cc: Ted Ts'o , linux-kernel@vger.kernel.org, xfs@oss.sgi.com, cluster-devel@redhat.com, cmm@us.ibm.com, Josef Bacik , joel.becker@oracle.com, linux-fsdevel@vger.kernel.org, linux-ext4@vger.kernel.org, linux-btrfs@vger.kernel.org On Tue, Jan 11, 2011 at 04:13:42PM -0500, Lawrence Greenfield wrote: > On Tue, Nov 9, 2010 at 6:40 PM, Dave Chinner wrote: > > The historical reason for such behaviour existing in XFS was that in > > 1997 the CPU and IO latency cost of unwritten extent conversion was > > significant, ..... > >> (Take for example a trusted cluster filesystem backend that checks the > >> object checksum before returning any data to the user; and if the > >> check fails the cluster file system will try to use some other replica > >> stored on some other server.) > > > > IOWs, all they want to do is avoid the unwritten extent conversion > > overhead. Time has shown that a bad security/performance tradeoff > > decision was made 13 years ago in XFS, so I see little reason to > > repeat it for ext4 today.... > > I'd make use of FALLOC_FL_EXPOSE_OLD_DATA. It's not the CPU overhead > of extent conversion. It's that extent conversion causes more metadata > operations than what you'd have otherwise, Yes, that's the "IO latency" part of the cost I mentioned above. > which means systems that > want to use O_DIRECT and make sure the data doesn't go away either > have to write O_DIRECT|O_DSYNC or need to call fdatasync(). Seriously, we tell application writers _all the time_ that they *must* use fsync/fdatasync to guarantee their data is on stable storage and that they cannot rely on side-effects of filesystem or storage specific behaviours (like ext3 ordered mode) to do that job for them. You're suggesting that by introducing FALLOC_FL_EXPOSE_OLD_DATA, applications can rely on filesystem/storage specific behaviour to guarantee data is on stable storage without the use of fdatasync/fsync. Wht you describe is definitely storage specific, because volatile write caches still needs the fdatasync to issue a cache flush. Do you see the same conflict here that I do? > cluster file system implementor Which one? Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs