From: "Darrick J. Wong" <darrick.wong@oracle.com> To: Ira Weiny <ira.weiny@intel.com> Cc: linux-kernel@vger.kernel.org, linux-xfs@vger.kernel.org, Al Viro <viro@zeniv.linux.org.uk>, Jan Kara <jack@suse.cz>, Dan Williams <dan.j.williams@intel.com>, Dave Chinner <david@fromorbit.com>, Christoph Hellwig <hch@lst.de>, "Theodore Y. Ts'o" <tytso@mit.edu>, Jeff Moyer <jmoyer@redhat.com>, linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-api@vger.kernel.org Subject: Re: [PATCH V11 04/11] Documentation/dax: Update Usage section Date: Tue, 28 Apr 2020 14:12:32 -0700 Message-ID: <20200428211232.GI6733@magnolia> (raw) In-Reply-To: <20200428205309.GA406458@iweiny-DESK2.sc.intel.com> On Tue, Apr 28, 2020 at 01:53:10PM -0700, Ira Weiny wrote: > On Tue, Apr 28, 2020 at 01:27:38PM -0700, Darrick J. Wong wrote: > > On Mon, Apr 27, 2020 at 05:21:35PM -0700, ira.weiny@intel.com wrote: > > > From: Ira Weiny <ira.weiny@intel.com> > > > > > [snip] > > > > + > > > + 3. If the persistent FS_XFLAG_DAX flag is set on a directory, this flag will > > > + be inherited by all regular files and sub directories that are subsequently > > > > Well, I'm at the level of minor edits: "...and subdirectories that..." > > Done. > > > > > > + 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 > > > + setting of the S_DAX flag. Given underlying storage which supports DAX the > > > + following hold. > > > > "hold:" > > Dene. > > > > > > + > > > + "-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: Setting and inheritance affect FS_XFLAG_DAX at all times even when > > > + the file system is mounted with a dax option. > > > > We can also clear the flag at any time no matter the mount option state. > > Perhaps: > > > > "NOTE: Modifications to and inheritance behavior of FS_XFLAG_DAX remain > > the same even when the filesystem is mounted with a dax option." > > Done. > > > > > > + However, in-core inode state > > > + (S_DAX) will be overridden until the file system is remounted with > > > + dax=inode and the inode is evicted from kernel memory. > > > + > > > + 5. The DAX policy can be changed via: > > > > "The S_DAX policy". I don't want people to get confused. > > Done. > > > > > > + > > > + a) Set the parent directory FS_XFLAG_DAX as needed before files are created > > > + > > > + b) Set the appropriate dax="foo" mount option > > > + > > > + c) Change the FS_XFLAG_DAX on existing regular files and directories. This > > > + has runtime constraints and limitations that are described in 6) below. > > > > "Setting", and "Changing" at the front of these three bullet points? > > > > Were you to put these together as full sentences, you'd want them to > > read "The DAX policy can be changed via setting the parent directory > > FS_XFLAG_DAX..." > > > > Done. > > > > + > > > + 6. When changing the DAX policy via toggling the persistent FS_XFLAG_DAX flag, > > > > "When changing the S_DAX policy..." > > Done. > > > > > > + 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 acheived by: > > > > "achieved" > > Done. > > > > > > + > > > + i. drop-caches > > > + ii. a filesystem unmount and mount cycle > > > + 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 > > > +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: > > > > "...inheritance, here are..." > > Done. > > > > > > + > > > +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 systems dax mount option setting. > > > > "...and the file system's dax mount option string." > > No. I don't think string is the right word here. It is the setting not the > string which is controlling the behavior. How about: > > "...and the file system's dax mount option." Oops. I miscopied that; all I really wanted was the apostrophe-s after "file system". "...and the file system's dax mount option setting." would have been fine. --D > > > > > > + > > > +statx can be used to query S_DAX. NOTE that a directory will never have S_DAX > > > > "Note that only regular files will ever have S_DAX set..."? > > Done. > > Ira > > > > > --D > > > > > +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 underlying media does not support dax and/or the file system is overridden > > > +with a mount option. > > > + > > > > > > > > > Implementation Tips for Block Driver Writers > > > -- > > > 2.25.1 > > >
next prev parent reply index Thread overview: 29+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-04-28 0:21 [PATCH V11 00/11] XFS - Enable per-file/per-directory DAX operations V11 ira.weiny 2020-04-28 0:21 ` [PATCH V11 01/11] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny 2020-04-28 0:21 ` [PATCH V11 02/11] fs: Remove unneeded IS_DAX() check in io_is_direct() ira.weiny 2020-04-28 0:21 ` [PATCH V11 03/11] fs/stat: Define DAX statx attribute ira.weiny 2020-04-28 0:21 ` [PATCH V11 04/11] Documentation/dax: Update Usage section ira.weiny 2020-04-28 20:27 ` Darrick J. Wong 2020-04-28 20:53 ` Ira Weiny 2020-04-28 21:12 ` Darrick J. Wong [this message] 2020-04-28 22:21 ` [PATCH V11.1] " ira.weiny 2020-04-29 2:21 ` Randy Dunlap 2020-04-29 4:30 ` Ira Weiny 2020-04-29 4:33 ` [PATCH V11.2] " ira.weiny 2020-04-29 5:47 ` Randy Dunlap 2020-04-28 0:21 ` [PATCH V11 05/11] fs/xfs: Change XFS_MOUNT_DAX to XFS_MOUNT_DAX_ALWAYS ira.weiny 2020-04-28 0:21 ` [PATCH V11 06/11] fs/xfs: Make DAX mount option a tri-state ira.weiny 2020-04-28 20:08 ` Darrick J. Wong 2020-04-28 0:21 ` [PATCH V11 07/11] fs/xfs: Create function xfs_inode_should_enable_dax() ira.weiny 2020-04-28 0:21 ` [PATCH V11 08/11] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() ira.weiny 2020-04-28 0:21 ` [PATCH V11 09/11] fs: Lift XFS_IDONTCACHE to the VFS layer ira.weiny 2020-04-28 20:06 ` Darrick J. Wong 2020-04-28 0:21 ` [PATCH V11 10/11] fs: Introduce DCACHE_DONTCACHE ira.weiny 2020-04-28 13:04 ` Jan Kara 2020-04-28 20:09 ` Darrick J. Wong 2020-04-28 0:21 ` [PATCH V11 11/11] fs/xfs: Update xfs_ioctl_setattr_dax_invalidate() ira.weiny 2020-04-28 20:11 ` Darrick J. Wong 2020-06-02 17:23 ` Darrick J. Wong 2020-06-02 23:15 ` Ira Weiny 2020-06-03 10:10 ` Jan Kara 2020-06-03 17:03 ` Darrick J. Wong
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