Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932310AbcDAOer (ORCPT ); Fri, 1 Apr 2016 10:34:47 -0400 Received: from mx0a-00082601.pphosted.com ([67.231.145.42]:50233 "EHLO mx0a-00082601.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759215AbcDAOep (ORCPT ); Fri, 1 Apr 2016 10:34:45 -0400 Subject: Re: [PATCHSET v3][RFC] Make background writeback not suck To: Dave Chinner References: <1459350477-16404-1-git-send-email-axboe@fb.com> <20160331082433.GO11812@dastard> <56FD344F.70908@fb.com> <20160401004623.GT11812@dastard> <56FDEA2D.2030207@fb.com> <20160401062745.GY11812@dastard> CC: , , From: Jens Axboe Message-ID: <56FE8702.6030306@fb.com> Date: Fri, 1 Apr 2016 08:34:42 -0600 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.6.0 MIME-Version: 1.0 In-Reply-To: <20160401062745.GY11812@dastard> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit X-Originating-IP: [192.168.54.13] X-Proofpoint-Spam-Reason: safe X-FB-Internal: Safe X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10432:,, definitions=2016-04-01_06:,, signatures=0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1444 Lines: 38 On 04/01/2016 12:27 AM, Dave Chinner wrote: > On Thu, Mar 31, 2016 at 09:25:33PM -0600, Jens Axboe wrote: >> On 03/31/2016 06:46 PM, Dave Chinner wrote: >>>>> virtio in guest, XFS direct IO -> no-op -> scsi in host. >>>> >>>> That has write back caching enabled on the guest, correct? >>> >>> No. It uses virtio,cache=none (that's the "XFS Direct IO" bit above). >>> Sorry for not being clear about that. >> >> That's fine, it's one less worry if that's not the case. So if you >> cat the 'write_cache' file in the virtioblk sysfs block queue/ >> directory, it says 'write through'? Just want to confirm that we got >> that propagated correctly. > > No such file. But I did find: > > $ cat /sys/block/vdc/cache_type > write back > > Which is what I'd expect it to safe given the man page description > of cache=none: > > Note that this is considered a writeback mode and the guest > OS must handle the disk write cache correctly in order to > avoid data corruption on host crashes. > > To make it say "write through" I need to use cache=directsync, but > I have no need for such integrity guarantees on a volatile test > device... I wasn't as concerned about the integrity side, more if it's flagged as write back then we induce further throttling. But I'll see if I can get your test case reproduced, then I don't see why it can't get fixed. I'm off all of next week though, so probably won't be until the week after... -- Jens Axboe