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=-10.7 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,NICE_REPLY_A, SPF_HELO_NONE,SPF_PASS,USER_AGENT_SANE_1 autolearn=ham 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 08ADBC432BE for ; Fri, 27 Aug 2021 15:35:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id DD3E260FF2 for ; Fri, 27 Aug 2021 15:35:58 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231964AbhH0Pgr (ORCPT ); Fri, 27 Aug 2021 11:36:47 -0400 Received: from sandeen.net ([63.231.237.45]:40676 "EHLO sandeen.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231700AbhH0Pgq (ORCPT ); Fri, 27 Aug 2021 11:36:46 -0400 Received: from liberator.sandeen.net (liberator.sandeen.net [10.0.0.147]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by sandeen.net (Postfix) with ESMTPSA id 318047BDB; Fri, 27 Aug 2021 10:35:34 -0500 (CDT) To: Bill O'Donnell Cc: "Darrick J. Wong" , Bill O'Donnell , linux-xfs@vger.kernel.org References: <20210826173012.273932-1-bodonnel@redhat.com> <20210826180947.GL12640@magnolia> <20210826220841.jsdlbquqq55cetnu@redhat.com> <9a9d54bd-42a5-45c7-38b2-dec12c49defc@sandeen.net> <20210827140312.vzrwee5keck67w5p@redhat.com> <0876d0d8-557a-db32-f2c3-9d976cab6fad@sandeen.net> <20210827142509.bjovj2l75xjoqd6w@redhat.com> From: Eric Sandeen Subject: Re: [PATCH] xfs: dax: facilitate EXPERIMENTAL warning for dax=inode case Message-ID: <0db1a400-8e01-2062-c49c-9538b5685dbb@sandeen.net> Date: Fri, 27 Aug 2021 10:35:56 -0500 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:78.0) Gecko/20100101 Thunderbird/78.13.0 MIME-Version: 1.0 In-Reply-To: <20210827142509.bjovj2l75xjoqd6w@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-xfs@vger.kernel.org On 8/27/21 9:25 AM, Bill O'Donnell wrote: > On Fri, Aug 27, 2021 at 09:18:32AM -0500, Eric Sandeen wrote: >> On 8/27/21 9:03 AM, Bill O'Donnell wrote: >>> On Thu, Aug 26, 2021 at 06:43:44PM -0500, Eric Sandeen wrote: >>>> On 8/26/21 5:08 PM, Bill O'Donnell wrote: >>>>> On Thu, Aug 26, 2021 at 01:16:22PM -0500, Eric Sandeen wrote: >>>>>> >>>>>> On 8/26/21 1:09 PM, Darrick J. Wong wrote: >>>>>>> On Thu, Aug 26, 2021 at 12:30:12PM -0500, Bill O'Donnell wrote: >>>>>> >>>>>>>> @@ -1584,7 +1586,7 @@ xfs_fs_fill_super( >>>>>>>> if (xfs_has_crc(mp)) >>>>>>>> sb->s_flags |= SB_I_VERSION; >>>>>>>> - if (xfs_has_dax_always(mp)) { >>>>>>>> + if (xfs_has_dax_always(mp) || xfs_has_dax_inode(mp)) { >>>>>>> >>>>>>> Er... can't this be done without burning another feature bit by: >>>>>>> >>>>>>> if (xfs_has_dax_always(mp) || (!xfs_has_dax_always(mp) && >>>>>>> !xfs_has_dax_never(mp))) { >>>>>>> ... >>>>>>> xfs_warn(mp, "DAX IS EXPERIMENTAL"); >>>>>>> } >>>>>> >>>>>> changing this conditional in this way will also fail dax=inode mounts on >>>>>> reflink-capable (i.e. default) filesystems, no? >>>>> >>>>> Correct. My original patch tests fine, and still handles the reflink and dax >>>>> incompatibility. The new suggested logic is problematic. >>>>> -Bill >>>> >>>> I think that both your proposed patch and Darrick's suggestion have this problem. >>>> >>>> "mount -o dax=inode" makes your new xfs_has_dax_inode(mp) true, and in that >>>> conditional, if the filesystem has reflink enabled, mount fails: >>>> >>>> # mkfs.xfs -f /dev/pmem0p1 >>>> meta-data=/dev/pmem0p1 isize=512 agcount=4, agsize=4194304 blks >>>> = sectsz=4096 attr=2, projid32bit=1 >>>> = crc=1 finobt=1, sparse=1, rmapbt=0 >>>> = reflink=1 bigtime=0 inobtcount=0 >>>> data = bsize=4096 blocks=16777216, imaxpct=25 >>>> = sunit=0 swidth=0 blks >>>> naming =version 2 bsize=4096 ascii-ci=0, ftype=1 >>>> log =internal log bsize=4096 blocks=8192, version=2 >>>> = sectsz=4096 sunit=1 blks, lazy-count=1 >>>> realtime =none extsz=4096 blocks=0, rtextents=0 >>>> >>>> # mount -o dax=inode /dev/pmem0p1 /mnt/test >>>> mount: wrong fs type, bad option, bad superblock on /dev/pmem0p1, >>>> missing codepage or helper program, or other error >>>> >>>> In some cases useful info is found in syslog - try >>>> dmesg | tail or so. >>>> >>>> # dmesg | tail -n 2 >>>> [ 192.691733] XFS (pmem0p1): DAX enabled. Warning: EXPERIMENTAL, use at your own risk >>>> [ 192.700300] XFS (pmem0p1): DAX and reflink cannot be used together! >>>> >>> >>> So, the "DAX enabled" is a misnomer in this case. However the incompatibility of DAX and reflink is >>> reflected in the next message, and indeed the mount fails. Is it now a matter of fixing >>> the message output so as not to indicate "DAX enabled..."? >> >> The mount should not fail, and it does not fail prior to your change. >> >> In the past, we did not allow any mixing of a reflink-capable >> filesystem with dax in any way. Now, with per-inode dax, dax-enabled inodes and >> reflink-enabled inodes can exist on the same filesystem, you just cannot have an >> inode which is both dax-enabled and reflinked at the same time. > > Ah. I missed that nuance. I had thought the incompatibility was > absolute. :/ > > The manpage for mkfs.xfs may need updating for the inode mode > (unless mine is old): > ----------------snip------------------ > "Note: the filesystem DAX mount option ( -o dax ) is incom‐ > patible with reflink-enabled XFS filesystems. To use > filesystem DAX with XFS, specify the -m reflink=0 option to > mkfs.xfs to disable the reflink feature." > ------------------------------------- Hm, looks like the xfs(5) manpage got updated, but it seems mkfs.xfs(8) did not. dax=value Set CPU direct access (DAX) behavior for the current filesystem. This mount option accepts the following values: "dax=inode" DAX will be enabled only on regular files with FS_XFLAG_DAX applied. "dax=never" DAX will not be enabled for any files. FS_XFLAG_DAX will be ignored. "dax=always" DAX will be enabled for all regular files, regardless of the FS_XFLAG_DAX state. If no option is used when mounting a filesystem stored on a DAX capable device, dax=inode will be used as default. For details regarding DAX behavior in kernel, please refer to ker‐ nel's documentation I'll send a patch to fix up the mkfs manpage, thanks. Thanks, -Eric