From mboxrd@z Thu Jan 1 00:00:00 1970 From: Matthew Wilcox Subject: Re: [Lsf] Preliminary Agenda and Activities for LSF Date: Wed, 30 Mar 2011 18:05:08 -0600 Message-ID: <20110331000508.GV13806@parisc-linux.org> References: <1301373398.2590.20.camel@mulgrave.site> <4D91BF90.8070909@redhat.com> <1301445210.2731.14.camel@mingming-laptop> <20110330021742.GL3008@dastard> <1301521798.7449.65.camel@mingming-laptop> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Dave Chinner , Ric Wheeler , James Bottomley , lsf@lists.linux-foundation.org, linux-fsdevel , "linux-scsi@vger.kernel.org" , device-mapper development To: Mingming Cao Return-path: Received: from palinux.external.hp.com ([192.25.206.14]:53542 "EHLO mail.parisc-linux.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754618Ab1CaAFM (ORCPT ); Wed, 30 Mar 2011 20:05:12 -0400 Content-Disposition: inline In-Reply-To: <1301521798.7449.65.camel@mingming-laptop> Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Wed, Mar 30, 2011 at 02:49:58PM -0700, Mingming Cao wrote: > > Direct IO semantics have always been that the application is allowed > > to overlap IO to the same range if it wants to. The result is > > undefined (just like issuing overlapping reads and writes to a disk > > at the same time) so it's the application's responsibility to avoid > > overlapping IO if it is a problem. > > I was thinking along the line to provide finer granularity lock to allow > concurrent direct IO to different offset/range, but to same offset, they > have to be serialized. If it's undefined behavior, i.e. overlapping is > allowed, then concurrent dio implementation is much easier. But not sure > if any apps currently using DIO aware of the ordering has to be done at > the application level. Yes, they're aware of it. And they consider it a bug if they ever do concurrent I/O to the same sector. -- Matthew Wilcox Intel Open Source Technology Centre "Bill, look, we understand that you're interested in selling us this operating system, but compare it to ours. We can't possibly take such a retrograde step."