From mboxrd@z Thu Jan 1 00:00:00 1970 From: Josef Bacik Subject: Re: testing stable pages being modified Date: Fri, 31 May 2013 09:29:07 -0400 Message-ID: <20130531132907.GF9829@localhost.localdomain> References: <20130530223610.GA24721@lenny.home.zabbo.net> <20130531051158.7927.24213@localhost.localdomain> <20130531062430.GB24721@lenny.home.zabbo.net> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Cc: Chris Mason , "linux-fsdevel@vger.kernel.org" , "linux-btrfs@vger.kernel.org" To: Zach Brown Return-path: Content-Disposition: inline In-Reply-To: <20130531062430.GB24721@lenny.home.zabbo.net> Sender: linux-btrfs-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Fri, May 31, 2013 at 12:24:30AM -0600, Zach Brown wrote: > > Changing O_DIRECT in flight has always been a deep dark corner case, and > > crc errors are the expected result. Have you found anyone doing this in > > real life? > > Agreed; and no, I haven't heard of people accidentally modifying stable > pages. > Windows does this, it also will send down the same page for different offsets which is why we have that special check in check_direct_IO for reads because that would cause lots of csum errors too. I tried to fix the modified in flight problem by checking the csums of the pages in the io completion handler and re-submitting the IO if the pages had changed, but this of course dramatically reduced performance for all of those well behaved O_DIRECT applications, so in the end I just set nodatasum for that vm image and carried on. I'm not sure what the solution is for this problem. Thanks, Josef