From mboxrd@z Thu Jan 1 00:00:00 1970 From: Anthony Liguori Subject: Re: JFYI: ext4 bug triggerable by kvm Date: Tue, 17 Aug 2010 09:44:49 -0500 Message-ID: <4C6AA061.80704@codemonkey.ws> References: <4C694483.5010903@msgid.tls.msk.ru> <4C694E7D.3060600@codemonkey.ws> <20100816184237.GA16579@infradead.org> <4C69A0C4.2080102@codemonkey.ws> <20100817090755.GA11110@infradead.org> <4C6A86E4.9080600@codemonkey.ws> <20100817130702.GA16635@infradead.org> <4C6A9AB5.6050404@codemonkey.ws> <20100817142808.GA22412@infradead.org> <4C6A9F4F.8040209@msgid.tls.msk.ru> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: Christoph Hellwig , KVM list , Kevin Wolf To: Michael Tokarev Return-path: Received: from mail-gy0-f174.google.com ([209.85.160.174]:58817 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754385Ab0HQOoz (ORCPT ); Tue, 17 Aug 2010 10:44:55 -0400 Received: by gyd8 with SMTP id 8so20690gyd.19 for ; Tue, 17 Aug 2010 07:44:54 -0700 (PDT) In-Reply-To: <4C6A9F4F.8040209@msgid.tls.msk.ru> Sender: kvm-owner@vger.kernel.org List-ID: On 08/17/2010 09:40 AM, Michael Tokarev wrote: > >>> fsync() being slow is orthogonal to my point. I don't see why we >>> need to do an fsync() on *every* write. It should only be necessary >>> when a guest injects an actual barrier. >>> > We don't do sync on every write, but O_SYNC implies that. > And apparently it is what happening behind the scenes in > ext4 O_SYNC case. > I think the real issue is we're mixing host configuration with guest visible state. With O_SYNC, we're causing cache=writethrough to do writethrough through two layers of the storage heirarchy. I don't think that's necessary or desirable though. Regards, Anthony Liguori > But ok.... > > /mjt >