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From: Ira Weiny <ira.weiny@intel.com>
To: Jeff Moyer <jmoyer@redhat.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
	"Darrick J. Wong" <darrick.wong@oracle.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Dave Chinner <david@fromorbit.com>,
	Christoph Hellwig <hch@lst.de>,
	"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
	linux-ext4 <linux-ext4@vger.kernel.org>,
	linux-xfs <linux-xfs@vger.kernel.org>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH v3 00/12] Enable per-file/directory DAX operations V3
Date: Fri, 14 Feb 2020 13:58:00 -0800
Message-ID: <20200214215759.GA20548@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <x4936bcdfso.fsf@segfault.boston.devel.redhat.com>

On Fri, Feb 14, 2020 at 04:23:19PM -0500, Jeff Moyer wrote:
> Ira Weiny <ira.weiny@intel.com> writes:
> 
> > [disclaimer: the following assumes the underlying 'device' (superblock)
> > supports DAX]
> >
> > ... which results in S_DAX == false when the file is opened without the mount
> > option.  The key would be that all directories/files created under a root with
> > XFS_DIFLAG2_DAX == true would inherit their flag and be XFS_DIFLAG2_DAX == true
> > all the way down the tree.  Any file not wanting DAX would need to set
> > XFS_DIFLAG2_DAX == false.  And setting false could be used on a directory to
> > allow a user or group to not use dax on files in that sub-tree.
> >
> > Then without '-o dax' (XFS_MOUNT_DAX == false) all files when opened set S_DAX
> > equal to XFS_DIFLAG2_DAX value.  (Directories, as of V4, never get S_DAX set.)
> >
> > If '-o dax' (XFS_MOUNT_DAX == true) then S_DAX is set on all files.
> 
> One more clarifying question.  Let's say I set XFS_DIFLAG2_DAX on an
> inode.  I then open the file, and perform mmap/load/store/etc.  I close
> the file, and I unset XFS_DIFLAG2_DAX.  Will the next open treat the
> file as S_DAX or not?  My guess is the inode won't be evicted, and so
> S_DAX will remain set.

The inode will not be evicted, or even it happens to be xfs_io will reload it
to unset the XFS_DIFLAG2_DAX flag.  And the S_DAX flag changes _with_ the
XFS_DIFLAG2_DAX change when it can (when the underlying storage supports
S_DAX).

Trying to change XFS_DIFLAG2_DAX while the file is mmap'ed returns -EBUSY.

Ira

> 
> The reason I ask is I've had requests from application developers to do
> just this.  They want to be able to switch back and forth between dax
> modes.
> 
> Thanks,
> Jeff
> 
> > [1] I'm beginning to think that if I type dax one more time I'm going to go
> > crazy...  :-P
> 
> dax dax dax!
> 

  reply index

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-02-08 19:34 ira.weiny
2020-02-08 19:34 ` [PATCH v3 01/12] fs/stat: Define DAX statx attribute ira.weiny
2020-02-08 19:34 ` [PATCH v3 02/12] fs/xfs: Isolate the physical DAX flag from effective ira.weiny
2020-02-08 19:34 ` [PATCH v3 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax() ira.weiny
2020-02-11  5:47   ` Dave Chinner
2020-02-11 16:13     ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 04/12] fs/xfs: Clean up DAX support check ira.weiny
2020-02-11  5:57   ` Dave Chinner
2020-02-11 16:28     ` Ira Weiny
2020-02-11 20:38       ` Dave Chinner
2020-02-08 19:34 ` [PATCH v3 05/12] fs: remove unneeded IS_DAX() check ira.weiny
2020-02-11  5:34   ` Dave Chinner
2020-02-11 16:38     ` Ira Weiny
2020-02-11 20:41       ` Dave Chinner
2020-02-12 16:04         ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 06/12] fs/xfs: Check if the inode supports DAX under lock ira.weiny
2020-02-11  6:16   ` Dave Chinner
2020-02-11 17:55     ` Ira Weiny
2020-02-11 20:42       ` Dave Chinner
2020-02-12 16:10         ` Ira Weiny
2020-02-08 19:34 ` [PATCH v3 07/12] fs: Add locking for a dynamic DAX state ira.weiny
2020-02-11  8:00   ` Dave Chinner
2020-02-11 20:14     ` Ira Weiny
2020-02-11 20:59       ` Dan Williams
2020-02-11 21:49       ` Dave Chinner
2020-02-12  6:31         ` Darrick J. Wong
2020-02-08 19:34 ` [PATCH v3 08/12] fs/xfs: Clarify lockdep dependency for xfs_isilocked() ira.weiny
2020-02-08 19:34 ` [PATCH v3 09/12] fs/xfs: Add write DAX lock to xfs layer ira.weiny
2020-02-08 19:34 ` [PATCH v3 10/12] fs: Prevent DAX state change if file is mmap'ed ira.weiny
2020-02-08 19:34 ` [PATCH v3 11/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-02-08 19:34 ` [PATCH v3 12/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny
2020-02-10 15:15 ` [PATCH v3 00/12] Enable per-file/directory DAX operations V3 Jeff Moyer
2020-02-11 20:17   ` Ira Weiny
2020-02-12 19:49     ` Jeff Moyer
2020-02-13 19:01       ` Ira Weiny
2020-02-13 19:05         ` Ira Weiny
2020-02-13 19:58           ` Darrick J. Wong
2020-02-13 23:29             ` Ira Weiny
2020-02-14  0:16               ` Dan Williams
2020-02-14 20:06                 ` Ira Weiny
2020-02-14 21:23                   ` Jeff Moyer
2020-02-14 21:58                     ` Ira Weiny [this message]
2020-02-14 22:06                       ` Jeff Moyer
2020-02-14 22:58                         ` Jeff Moyer
2020-02-14 23:03                           ` Jeff Moyer
2020-02-18  2:35                           ` Ira Weiny
2020-02-18 14:22                             ` Jeff Moyer
2020-02-18 23:54                               ` Ira Weiny
2020-02-20 16:20                                 ` Ira Weiny
2020-02-20 16:30                                   ` Darrick J. Wong
2020-02-20 16:49                                     ` Ira Weiny
2020-02-20 17:00                                       ` Darrick J. Wong

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