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=-5.3 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,NICE_REPLY_A,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 17A2FC433E9 for ; Mon, 1 Mar 2021 07:43:15 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id CFBAB64E40 for ; Mon, 1 Mar 2021 07:43:14 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232575AbhCAHlS (ORCPT ); Mon, 1 Mar 2021 02:41:18 -0500 Received: from esa5.hc1455-7.c3s2.iphmx.com ([68.232.139.130]:34593 "EHLO esa5.hc1455-7.c3s2.iphmx.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232574AbhCAHlR (ORCPT ); Mon, 1 Mar 2021 02:41:17 -0500 IronPort-SDR: tGvBDWbOft83eNsQjRioYLiVBVz1iyTh5nEUdQtY/rAjCbWstI0P576mQxG76VXSQw4xGhrL2O 4pwBXFGLFfhyEbZhAR/Mgsk0Y5Jr5w8MEPfKH8NLh/OX8XS0Nr1OYGhwmOZpX+d7dbK3mK+0Zu k6MIMtLyZivYsUNlCwnuq4wnqvQFqUY3d/d+V53NnFfS+l32tQyX/4P0l4NjWnCus3LwP1B33G r72yxnXbCv2gEGqjmBh+qABH4oGmwPuvAC4E8deFIwy0n12gZGnaDb5KFX3wnOvJPF3pKE4Q81 sgE= X-IronPort-AV: E=McAfee;i="6000,8403,9909"; a="20943770" X-IronPort-AV: E=Sophos;i="5.81,214,1610377200"; d="scan'208";a="20943770" Received: from unknown (HELO oym-r2.gw.nic.fujitsu.com) ([210.162.30.90]) by esa5.hc1455-7.c3s2.iphmx.com with ESMTP; 01 Mar 2021 16:26:47 +0900 Received: from oym-m3.gw.nic.fujitsu.com (oym-nat-oym-m3.gw.nic.fujitsu.com [192.168.87.60]) by oym-r2.gw.nic.fujitsu.com (Postfix) with ESMTP id CC3C2E60A7; Mon, 1 Mar 2021 16:26:46 +0900 (JST) Received: from m3050.s.css.fujitsu.com (msm.b.css.fujitsu.com [10.134.21.208]) by oym-m3.gw.nic.fujitsu.com (Postfix) with ESMTP id D3CCE15331; Mon, 1 Mar 2021 16:26:45 +0900 (JST) Received: from [10.133.113.145] (VPC-Y08P0560117.g01.fujitsu.local [10.133.113.145]) by m3050.s.css.fujitsu.com (Postfix) with ESMTP id A473F2A7; Mon, 1 Mar 2021 16:26:45 +0900 (JST) Subject: Re: Question about the "EXPERIMENTAL" tag for dax in XFS To: Dan Williams , "Darrick J. Wong" Cc: "ruansy.fnst@fujitsu.com" , "linux-kernel@vger.kernel.org" , "linux-xfs@vger.kernel.org" , "linux-nvdimm@lists.01.org" , "linux-fsdevel@vger.kernel.org" , "darrick.wong@oracle.com" , "willy@infradead.org" , "jack@suse.cz" , "viro@zeniv.linux.org.uk" , "linux-btrfs@vger.kernel.org" , "ocfs2-devel@oss.oracle.com" , "david@fromorbit.com" , "hch@lst.de" , "rgoldwyn@suse.de" , "qi.fuli@fujitsu.com" , "fnstml-iaas@cn.fujitsu.com" References: <20210226002030.653855-1-ruansy.fnst@fujitsu.com> <20210226190454.GD7272@magnolia> From: Yasunori Goto Message-ID: <556921a1-456c-c24d-6d47-e8b15c1d9972@fujitsu.com> Date: Mon, 1 Mar 2021 16:26:45 +0900 User-Agent: Mozilla/5.0 (Windows NT 6.3; WOW64; rv:68.0) Gecko/20100101 Thunderbird/68.12.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 7bit X-TM-AS-GCONF: 00 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org Hello, Dan-san, On 2021/02/27 4:24, Dan Williams wrote: > On Fri, Feb 26, 2021 at 11:05 AM Darrick J. Wong wrote: >> >> On Fri, Feb 26, 2021 at 09:45:45AM +0000, ruansy.fnst@fujitsu.com wrote: >>> Hi, guys >>> >>> Beside this patchset, I'd like to confirm something about the >>> "EXPERIMENTAL" tag for dax in XFS. >>> >>> In XFS, the "EXPERIMENTAL" tag, which is reported in waring message >>> when we mount a pmem device with dax option, has been existed for a >>> while. It's a bit annoying when using fsdax feature. So, my initial >>> intention was to remove this tag. And I started to find out and solve >>> the problems which prevent it from being removed. >>> >>> As is talked before, there are 3 main problems. The first one is "dax >>> semantics", which has been resolved. The rest two are "RMAP for >>> fsdax" and "support dax reflink for filesystem", which I have been >>> working on. >> >> >> >>> So, what I want to confirm is: does it means that we can remove the >>> "EXPERIMENTAL" tag when the rest two problem are solved? >> >> Yes. I'd keep the experimental tag for a cycle or two to make sure that >> nothing new pops up, but otherwise the two patchsets you've sent close >> those two big remaining gaps. Thank you for working on this! >> >>> Or maybe there are other important problems need to be fixed before >>> removing it? If there are, could you please show me that? >> >> That remains to be seen through QA/validation, but I think that's it. >> >> Granted, I still have to read through the two patchsets... > > I've been meaning to circle back here as well. > > My immediate concern is the issue Jason recently highlighted [1] with > respect to invalidating all dax mappings when / if the device is > ripped out from underneath the fs. I don't think that will collide > with Ruan's implementation, but it does need new communication from > driver to fs about removal events. > > [1]: http://lore.kernel.org/r/CAPcyv4i+PZhYZiePf2PaH0dT5jDfkmkDX-3usQy1fAhf6LPyfw@mail.gmail.com > I'm not sure why there is a race condition between unbinding operation and accessing mmaped file on filesystem dax yet. May be silly question, but could you tell me why the "unbinding" operation of the namespace which is mounted by filesystem dax must be allowed? If "unbinding" is rejected when the filesystem is mounted with dax enabled, what is inconvenience? I can imagine if a device like usb memory stick is removed surprisingly, kernel/filesystem need to reject writeback at the time, and discard page cache. Then, I can understand that unbinding operation is essential for such case. But I don't know why PMEM device/namespace allows unbinding operation like surprising removal event. Thanks, -- Yasunori Goto