From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-2.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 827ECC433DF for ; Wed, 10 Jun 2020 05:05:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 63EE72074B for ; Wed, 10 Jun 2020 05:05:25 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1725999AbgFJFFT (ORCPT ); Wed, 10 Jun 2020 01:05:19 -0400 Received: from mail110.syd.optusnet.com.au ([211.29.132.97]:40858 "EHLO mail110.syd.optusnet.com.au" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725844AbgFJFFS (ORCPT ); Wed, 10 Jun 2020 01:05:18 -0400 Received: from dread.disaster.area (pa49-180-124-177.pa.nsw.optusnet.com.au [49.180.124.177]) by mail110.syd.optusnet.com.au (Postfix) with ESMTPS id A3E12108DD1; Wed, 10 Jun 2020 15:05:14 +1000 (AEST) Received: from dave by dread.disaster.area with local (Exim 4.92.3) (envelope-from ) id 1jisvG-0003Er-1u; Wed, 10 Jun 2020 15:05:10 +1000 Date: Wed, 10 Jun 2020 15:05:10 +1000 From: Dave Chinner To: Goldwyn Rodrigues Cc: darrick.wong@oracle.com, linux-btrfs@vger.kernel.org, fdmanana@gmail.com, linux-fsdevel@vger.kernel.org, hch@lst.de, linux-xfs@vger.kernel.org Subject: Re: [PATCH 0/3] Transient errors in Direct I/O Message-ID: <20200610050510.GL2040@dread.disaster.area> References: <20200605204838.10765-1-rgoldwyn@suse.de> <20200610025900.GA2005@dread.disaster.area> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200610025900.GA2005@dread.disaster.area> User-Agent: Mutt/1.10.1 (2018-07-13) X-Optus-CM-Score: 0 X-Optus-CM-Analysis: v=2.3 cv=X6os11be c=1 sm=1 tr=0 a=k3aV/LVJup6ZGWgigO6cSA==:117 a=k3aV/LVJup6ZGWgigO6cSA==:17 a=kj9zAlcOel0A:10 a=nTHF0DUjJn0A:10 a=7-415B0cAAAA:8 a=5l335YXG8XPxeSgPGoIA:9 a=CjuIK1q_8ugA:10 a=biEYGPWJfzWAr4FL6Ov7:22 Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Wed, Jun 10, 2020 at 12:59:00PM +1000, Dave Chinner wrote: > [ Please cc the XFS list on XFS and iomap infrastructure changes.] > > On Fri, Jun 05, 2020 at 03:48:35PM -0500, Goldwyn Rodrigues wrote: > > In current scenarios, for XFS, it would mean that a page invalidation > > would end up being a writeback error. So, if iomap returns zero, fall > > back to biffered I/O. XFS has never supported fallback to buffered I/O. > > I hope it is not "never will" ;) > > I wouldn't say "never", but we are not going to change XFS behaviour > because btrfs has a page invalidation vs DIO bug in it... Let me point out a specific "oh shit, I didn't think of that" sort of problem that your blind fallback to buffered IO causes. Do this via direct IO: pwritev2(RWF_NOWAIT) now have it fail invalidation in the direct IO path and fallback to buffered write. What does buffered write do with it? if (iocb->ki_flags & IOCB_NOWAIT) return -EOPNOTSUPP; Yup, userspace gets a completely spurious and bogus -EOPNOTSUPP error to pwritev2() because some 3rd party is accessing the same file via mmap or buffered IO. Cheers, Dave. -- Dave Chinner david@fromorbit.com