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 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 53B0EC433EF for ; Tue, 26 Oct 2021 14:12:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 37D4060F90 for ; Tue, 26 Oct 2021 14:12:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236448AbhJZOOp (ORCPT ); Tue, 26 Oct 2021 10:14:45 -0400 Received: from out30-133.freemail.mail.aliyun.com ([115.124.30.133]:36654 "EHLO out30-133.freemail.mail.aliyun.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236431AbhJZOOo (ORCPT ); Tue, 26 Oct 2021 10:14:44 -0400 X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R181e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=e01e04394;MF=jefflexu@linux.alibaba.com;NM=1;PH=DS;RN=10;SR=0;TI=SMTPD_---0Utn9eYf_1635257537; Received: from admindeMacBook-Pro-2.local(mailfrom:jefflexu@linux.alibaba.com fp:SMTPD_---0Utn9eYf_1635257537) by smtp.aliyun-inc.com(127.0.0.1); Tue, 26 Oct 2021 22:12:18 +0800 To: Theodore Ts'o , adilger.kernel@dilger.ca, "Darrick J. Wong" , ira.weiny@intel.com Cc: linux-xfs@vger.kernel.org, "linux-ext4@vger.kernel.org" , linux-fsdevel@vger.kernel.org, dan.j.williams@intel.com, Vivek Goyal , Christoph Hellwig From: JeffleXu Subject: [Question] ext4/xfs: Default behavior changed after per-file DAX Message-ID: <26ddaf6d-fea7-ed20-cafb-decd63b2652a@linux.alibaba.com> Date: Tue, 26 Oct 2021 22:12:17 +0800 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.14.0 MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org Hi, Recently I'm working on supporting per-file DAX for virtiofs [1]. Vivek Goyal and I are interested [2] why the default behavior has changed since introduction of per-file DAX on ext4 and xfs [3][4]. That is, before the introduction of per-file DAX, when user doesn't specify '-o dax', DAX is disabled for all files. After supporting per-file DAX, when neither '-o dax' nor '-o dax=always|inode|never' is specified, it actually works in a '-o dax=inode' way if the underlying blkdev is DAX capable, i.e. depending on the persistent inode flag. That is, the default behavior has changed from user's perspective. We are not sure if this is intentional or not. Appreciate if anyone could offer some hint. [1] https://lore.kernel.org/all/YW2Oj4FrIB8do3zX@redhat.com/T/ [2] https://lore.kernel.org/all/YW2Oj4FrIB8do3zX@redhat.com/T/#mf067498887ca2023c64c8b8f6aec879557eb28f8 [3] 9cb20f94afcd2964944f9468e38da736ee855b19 ("fs/ext4: Make DAX mount option a tri-state") [4] 02beb2686ff964884756c581d513e103542dcc6a ("fs/xfs: Make DAX mount option a tri-state") -- Thanks, Jeffle