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,URIBL_BLOCKED,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 D9B20C3A59B for ; Fri, 30 Aug 2019 15:35:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id B543822CE9 for ; Fri, 30 Aug 2019 15:35:24 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727938AbfH3PfV (ORCPT ); Fri, 30 Aug 2019 11:35:21 -0400 Received: from mx2.suse.de ([195.135.220.15]:43700 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727434AbfH3PfV (ORCPT ); Fri, 30 Aug 2019 11:35:21 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 9F91DABB2; Fri, 30 Aug 2019 15:35:20 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 0FABE1E43A8; Fri, 30 Aug 2019 17:35:20 +0200 (CEST) Date: Fri, 30 Aug 2019 17:35:20 +0200 From: Jan Kara To: Andreas Dilger Cc: Jan Kara , Dave Chinner , Joseph Qi , Theodore Ts'o , linux-ext4@vger.kernel.org Subject: Re: [PATCH 0/3] Revert parallel dio reads Message-ID: <20190830153520.GB25069@quack2.suse.cz> References: <1566871552-60946-1-git-send-email-joseph.qi@linux.alibaba.com> <20190827115118.GY7777@dread.disaster.area> <20190829105858.GA22939@quack2.suse.cz> <8C1DC2C7-4389-446D-8233-EEDAAD38C398@dilger.ca> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <8C1DC2C7-4389-446D-8233-EEDAAD38C398@dilger.ca> User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-ext4-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Thu 29-08-19 13:06:22, Andreas Dilger wrote: > On Aug 29, 2019, at 4:58 AM, Jan Kara wrote: > > > > On Tue 27-08-19 21:51:18, Dave Chinner wrote: > >> On Tue, Aug 27, 2019 at 10:05:49AM +0800, Joseph Qi wrote: > >>> This patch set is trying to revert parallel dio reads feature at present > >>> since it causes significant performance regression in mixed random > >>> read/write scenario. > >>> > >>> Joseph Qi (3): > >>> Revert "ext4: remove EXT4_STATE_DIOREAD_LOCK flag" > >>> Revert "ext4: fix off-by-one error when writing back pages before dio > >>> read" > >>> Revert "ext4: Allow parallel DIO reads" > >>> > >>> fs/ext4/ext4.h | 17 +++++++++++++++++ > >>> fs/ext4/extents.c | 19 ++++++++++++++----- > >>> fs/ext4/inode.c | 47 +++++++++++++++++++++++++++++++---------------- > >>> fs/ext4/ioctl.c | 4 ++++ > >>> fs/ext4/move_extent.c | 4 ++++ > >>> fs/ext4/super.c | 12 +++++++----- > >>> 6 files changed, 77 insertions(+), 26 deletions(-) > >> > >> Before doing this, you might want to have a chat and co-ordinate > >> with the folks that are currently trying to port the ext4 direct IO > >> code to use the iomap infrastructure: > >> > >> https://lore.kernel.org/linux-ext4/20190827095221.GA1568@poseidon.bobrowski.net/T/#t > >> > >> That is going to need the shared locking on read and will work just > >> fine with shared locking on write, too (it's the code that XFS uses > >> for direct IO). So it might be best here if you work towards shared > >> locking on the write side rather than just revert the shared locking > >> on the read side.... > > > > Yeah, after converting ext4 DIO path to iomap infrastructure, using shared > > inode lock for all aligned non-extending DIO writes will be easy so I'd > > prefer if we didn't have to redo the iomap conversion patches due to these > > reverts. > > But if the next kernel is LTS and the iomap implementation isn't in the > current merge window (very unlikely) then we're stuck with this performance > hit for LTS. It is also unlikely that LTS will take the revert patches if > they have not been landed to master. I agree this is not great but the regression is there for 3 years, it has been released in major distribution kernels quite a long time ago, and only now someone complained. So it doesn't seem many people care about performance of mixed RW workload when mounted with dioread_nolock (note that the patches actually improve performance of read-only DIO workload when not using dioread_nolock as for that case, exclusive lock is replaced with a shared one). Honza -- Jan Kara SUSE Labs, CR