From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Darrick J. Wong" Subject: Re: BLKZEROOUT + pread should return zeroes, right? Date: Thu, 16 Oct 2014 13:04:15 -0700 Message-ID: <20141016200415.GA16637@birch.djwong.org> References: <20141014030132.GA12013@birch.djwong.org> <20141014042711.GJ5267@dastard> <20141014060242.GA22878@birch.djwong.org> <20141014063210.GK9738@thunk.org> <20141015012534.GB12013@birch.djwong.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Theodore Ts'o" , Dave Chinner , Jens Axboe , linux-fsdevel@vger.kernel.org, linux-ext4 To: "Martin K. Petersen" Return-path: Received: from aserp1040.oracle.com ([141.146.126.69]:47204 "EHLO aserp1040.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751539AbaJPUEa (ORCPT ); Thu, 16 Oct 2014 16:04:30 -0400 Content-Disposition: inline In-Reply-To: Sender: linux-fsdevel-owner@vger.kernel.org List-ID: On Tue, Oct 14, 2014 at 09:32:25PM -0400, Martin K. Petersen wrote: > >>>>> "Darrick" == Darrick J Wong writes: > > Darrick> Well then let's change BLKZEROOUT to require O_DIRECT instead > Darrick> of hiding the coherency problem, > > That would break existing users, though. If they're using the existing BLKZEROOUT without O_DIRECT they're already broken. But I might as well just fix them quietly. --D > Darrick> A further optimization to mke2fs would be to detect that we've > Darrick> run discard-with-zeroes and therefore can skip issuing > Darrick> subsequent zeroouts on the same ranges, but I'm wary that > Darrick> discard-zeroes-data does what it purports to do. > > It's dubious. I'm working on making sure we only set discard_zeroes_data > when the device guarantees it for 3.19. > > -- > Martin K. Petersen Oracle Linux Engineering