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=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable 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 DF1DDC8300B for ; Wed, 29 Apr 2020 04:30:32 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id BD9922072A for ; Wed, 29 Apr 2020 04:30:32 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726684AbgD2EaK (ORCPT ); Wed, 29 Apr 2020 00:30:10 -0400 Received: from mga06.intel.com ([134.134.136.31]:50602 "EHLO mga06.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726451AbgD2EaK (ORCPT ); Wed, 29 Apr 2020 00:30:10 -0400 IronPort-SDR: jYZu44eXIBWA/fryfc467h1uVuDbLuH3bhwiT52xp6J0v1AYh4DITp9+QJfXdz41VwkD2VZYPb cZIGfeUer8NA== X-Amp-Result: SKIPPED(no attachment in message) X-Amp-File-Uploaded: False Received: from orsmga008.jf.intel.com ([10.7.209.65]) by orsmga104.jf.intel.com with ESMTP/TLS/ECDHE-RSA-AES256-GCM-SHA384; 28 Apr 2020 21:30:09 -0700 IronPort-SDR: gHgCiSj+Hez8F35uvvT9L8FD60mHGRbRpB8J+xGO4FEygI0TT2sBHolNaIU2dFvZBlsLXX1z9G 2OEDGXIQkZVQ== X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="5.73,330,1583222400"; d="scan'208";a="294066666" Received: from iweiny-desk2.sc.intel.com ([10.3.52.147]) by orsmga008.jf.intel.com with ESMTP; 28 Apr 2020 21:30:08 -0700 Date: Tue, 28 Apr 2020 21:30:08 -0700 From: Ira Weiny To: Randy Dunlap Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, "Darrick J. Wong" , Al Viro , Jan Kara , Dan Williams , Dave Chinner , Christoph Hellwig , "Theodore Y. Ts'o" , Jeff Moyer , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH V11.1] Documentation/dax: Update Usage section Message-ID: <20200429043008.GA410031@iweiny-DESK2.sc.intel.com> References: <20200428002142.404144-5-ira.weiny@intel.com> <20200428222145.409961-1-ira.weiny@intel.com> <28f97c0b-6c7f-7496-b57d-0342a4dcc0af@infradead.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <28f97c0b-6c7f-7496-b57d-0342a4dcc0af@infradead.org> User-Agent: Mutt/1.11.1 (2018-12-01) Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Tue, Apr 28, 2020 at 07:21:18PM -0700, Randy Dunlap wrote: > On 4/28/20 3:21 PM, ira.weiny@intel.com wrote: > > From: Ira Weiny > > > > Update the Usage section to reflect the new individual dax selection > > functionality. > > > > Signed-off-by: Ira Weiny > > > > --- > > Changes from V11: > > Minor changes from Darrick > > > > Changes from V10: > > Clarifications from Dave > > Add '-c' to xfs_io examples > > > > Changes from V9: > > Fix missing ')' > > Fix trialing '"' > > trailing Thanks > > > > > Changes from V8: > > Updates from Darrick > > > > Changes from V7: > > Cleanups/clarifications from Darrick and Dan > > > > Changes from V6: > > Update to allow setting FS_XFLAG_DAX any time. > > Update with list of behaviors from Darrick > > https://lore.kernel.org/lkml/20200409165927.GD6741@magnolia/ > > > > Changes from V5: > > Update to reflect the agreed upon semantics > > https://lore.kernel.org/lkml/20200405061945.GA94792@iweiny-DESK2.sc.intel.com/ > > --- > > Documentation/filesystems/dax.txt | 142 +++++++++++++++++++++++++++++- > > 1 file changed, 139 insertions(+), 3 deletions(-) > > > > diff --git a/Documentation/filesystems/dax.txt b/Documentation/filesystems/dax.txt > > index 679729442fd2..dc1c1aa36cc2 100644 > > --- a/Documentation/filesystems/dax.txt > > +++ b/Documentation/filesystems/dax.txt > > @@ -17,11 +17,147 @@ For file mappings, the storage device is mapped directly into userspace. > > Usage > > ----- > > > > -If you have a block device which supports DAX, you can make a filesystem > > +If you have a block device which supports DAX, you can make a file system > > on it as usual. The DAX code currently only supports files with a block > > size equal to your kernel's PAGE_SIZE, so you may need to specify a block > > -size when creating the filesystem. When mounting it, use the "-o dax" > > -option on the command line or add 'dax' to the options in /etc/fstab. > > +size when creating the file system. > > + > > +Currently 3 filesystems support DAX: ext2, ext4 and xfs. Enabling DAX on them > > Why "file system" in the first paragraph when "filesystem" is used here and below? AFAIK they are interchangeable. https://en.wikipedia.org/wiki/File_system But consistency is a reasonable request. The rest of the doc (save 1 place) uses filesystem so I will adopt that here, and clean up that 1 place. > > > +is different. > > + > > +Enabling DAX on ext4 and ext2 > > +----------------------------- > > + > > +When mounting the filesystem, use the "-o dax" option on the command line or > > +add 'dax' to the options in /etc/fstab. This works to enable DAX on all files > > +within the filesystem. It is equivalent to the '-o dax=always' behavior below. > > + > > + > > +Enabling DAX on xfs > > +------------------- > > + > > +Summary > > +------- > > + > > + 1. There exists an in-kernel file access mode flag S_DAX that corresponds to > > + the statx flag STATX_ATTR_DAX. See the manpage for statx(2) for details > > + about this access mode. > > + > > + 2. There exists a persistent flag FS_XFLAG_DAX that can be applied to regular > > + files and directories. This advisory flag can be set or cleared at any > > + time, but doing so does not immediately affect the S_DAX state. > > + > > + 3. If the persistent FS_XFLAG_DAX flag is set on a directory, this flag will > > + be inherited by all regular files and subdirectories that are subsequently > > + created in this directory. Files and subdirectories that exist at the time > > + this flag is set or cleared on the parent directory are not modified by > > + this modification of the parent directory. > > + > > + 4. There exists dax mount options which can override FS_XFLAG_DAX in the > > exist Ah yea, Done. > > > + setting of the S_DAX flag. Given underlying storage which supports DAX the > > + following hold: > > + > > + "-o dax=inode" means "follow FS_XFLAG_DAX" and is the default. > > + > > + "-o dax=never" means "never set S_DAX, ignore FS_XFLAG_DAX." > > + > > + "-o dax=always" means "always set S_DAX ignore FS_XFLAG_DAX." > > + > > + "-o dax" is a legacy option which is an alias for "dax=always". > > + This may be removed in the future so "-o dax=always" is > > + the preferred method for specifying this behavior. > > + > > + NOTE: Modifications to and the inheritance behavior of FS_XFLAG_DAX remain > > + the same even when the file system is mounted with a dax option. However, > > + in-core inode state (S_DAX) will be overridden until the file system is > > "file system" (2 times above) Done. > > > + remounted with dax=inode and the inode is evicted from kernel memory. > > + > > + 5. The S_DAX policy can be changed via: > > + > > + a) Setting the parent directory FS_XFLAG_DAX as needed before files are > > + created > > + > > + b) Setting the appropriate dax="foo" mount option > > + > > + c) Changing the FS_XFLAG_DAX on existing regular files and directories. > > FS_XFLAGS_DAX flag on Done. > > > + This has runtime constraints and limitations that are described in 6) > > + below. > > + > > + 6. When changing the S_DAX policy via toggling the persistent FS_XFLAG_DAX flag, > > + the change in behaviour for existing regular files may not occur > > + immediately. If the change must take effect immediately, the administrator > > + needs to: > > + > > + a) stop the application so there are no active references to the data set > > + the policy change will affect > > + > > + b) evict the data set from kernel caches so it will be re-instantiated when > > + the application is restarted. This can be achieved by: > > + > > + i. drop-caches > > + ii. a filesystem unmount and mount cycle > > filesystem Done. > > > + iii. a system reboot > > + > > + > > +Details > > +------- > > + > > +There are 2 per-file dax flags. One is a persistent inode setting (FS_XFLAG_DAX) > > +and the other is a volatile flag indicating the active state of the feature > > +(S_DAX). > > + > > +FS_XFLAG_DAX is preserved within the file system. This persistent config > > file system Done. > > > +setting can be set, cleared and/or queried using the FS_IOC_FS[GS]ETXATTR ioctl > > +(see ioctl_xfs_fsgetxattr(2)) or an utility such as 'xfs_io'. > > + > > +New files and directories automatically inherit FS_XFLAG_DAX from > > +their parent directory _when_ _created_. Therefore, setting FS_XFLAG_DAX at > > +directory creation time can be used to set a default behavior for an entire > > +sub-tree. > > + > > +To clarify inheritance, here are 3 examples: > > + > > +Example A: > > + > > +mkdir -p a/b/c > > +xfs_io -c 'chattr +x' a > > +mkdir a/b/c/d > > +mkdir a/e > > + > > + dax: a,e > > + no dax: b,c,d > > + > > +Example B: > > + > > +mkdir a > > +xfs_io -c 'chattr +x' a > > +mkdir -p a/b/c/d > > + > > + dax: a,b,c,d > > + no dax: > > + > > +Example C: > > + > > +mkdir -p a/b/c > > +xfs_io -c 'chattr +x' c > > +mkdir a/b/c/d > > + > > + dax: c,d > > + no dax: a,b > > + > > + > > +The current enabled state (S_DAX) is set when a file inode is instantiated in > > +memory by the kernel. It is set based on the underlying media support, the > > +value of FS_XFLAG_DAX and the file system's dax mount option. > > + > > +statx can be used to query S_DAX. NOTE that only regular files will ever have > > +S_DAX set and therefore statx will never indicate that S_DAX is set on > > +directories. > > + > > +Setting the FS_XFLAG_DAX (specifically or through inheritance) occurs even if > > the FS_XFLAG_DAX flag Done. > > > +the underlying media does not support dax and/or the file system is overridden > > file system > > Just be consistent, please. Fair enough, Done. > > > +with a mount option. > > + > > > > > > Implementation Tips for Block Driver Writers > > > > thanks. NP, Thank you! Ira > -- > ~Randy >