Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755747AbbHYOOa (ORCPT ); Tue, 25 Aug 2015 10:14:30 -0400 Received: from mx0b-00082601.pphosted.com ([67.231.153.30]:32021 "EHLO mx0b-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755134AbbHYOO2 (ORCPT ); Tue, 25 Aug 2015 10:14:28 -0400 Date: Tue, 25 Aug 2015 10:13:48 -0400 From: Chris Mason To: Jeff Moyer CC: Dave Chinner , Brian Norris , Artem Bityutskiy , Richard Weinberger , Dongsheng Yang , , , Subject: Re: [PATCH 2/2] ubifs: Allow O_DIRECT Message-ID: <20150825141348.GF7176@ret.masoncoding.com> Mail-Followup-To: Chris Mason , Jeff Moyer , Dave Chinner , Brian Norris , Artem Bityutskiy , Richard Weinberger , Dongsheng Yang , linux-mtd@lists.infradead.org, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org References: <1440016553-26481-2-git-send-email-richard@nod.at> <55D542C5.6040500@cn.fujitsu.com> <1440070300.31419.202.camel@gmail.com> <55D5BC92.8050903@nod.at> <20150820204933.GG74600@google.com> <1440400405.15510.29.camel@gmail.com> <20150824161837.GA28975@localhost> <20150824234611.GV3902@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.5.23.1 (2014-03-12) X-Originating-IP: [192.168.52.123] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:5.14.151,1.0.33,0.0.0000 definitions=2015-08-25_06:2015-08-24,2015-08-25,1970-01-01 signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2205 Lines: 48 On Tue, Aug 25, 2015 at 10:00:58AM -0400, Jeff Moyer wrote: > Dave Chinner writes: > > > On Mon, Aug 24, 2015 at 01:19:24PM -0400, Jeff Moyer wrote: > >> Brian Norris writes: > >> > >> > On Mon, Aug 24, 2015 at 10:13:25AM +0300, Artem Bityutskiy wrote: > >> >> Now, some user-space fails when direct I/O is not supported. > >> > > >> > I think the whole argument rested on what it means when "some user space > >> > fails"; apparently that "user space" is just a test suite (which > >> > can/should be fixed). > >> > >> Even if it wasn't a test suite it should still fail. Either the fs > >> supports O_DIRECT or it doesn't. Right now, the only way an application > >> can figure this out is to try an open and see if it fails. Don't break > >> that. > > > > Who cares how a filesystem implements O_DIRECT as long as it does > > not corrupt data? ext3 fell back to buffered IO in many situations, > > yet the only complaints about that were performance. IOWs, it's long been > > true that if the user cares about O_DIRECT *performance* then they > > have to be careful about their choice of filesystem. > > > But if it's only 5 lines of code per filesystem to support O_DIRECT > > *correctly* via buffered IO, then exactly why should userspace have > > to jump through hoops to explicitly handle open(O_DIRECT) failure? > > > Especially when you consider that all they can do is fall back to > > buffered IO themselves.... > > I had written counterpoints for all of this, but I thought better of > it. Old versions of the kernel simply ignore O_DIRECT, so clearly > there's precedent. > > I do think we should at least document what file systems appear to be > doing. Here's a man page patch for open (generated with extra context > for easier reading). Let me know what you think. We shouldn't be ignoring it, but instead call it similar to O_DSYNC plus removing the pages from cache. -chris -- 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/