From: Ira Weiny <ira.weiny@intel.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
Jeff Moyer <jmoyer@redhat.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 12:06:07 -0800 [thread overview]
Message-ID: <20200214200607.GA18593@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <CAPcyv4hkWoC+xCqicH1DWzmU2DcpY0at_A6HaBsrdLbZ6qzWow@mail.gmail.com>
On Thu, Feb 13, 2020 at 04:16:17PM -0800, Dan Williams wrote:
> On Thu, Feb 13, 2020 at 3:29 PM Ira Weiny <ira.weiny@intel.com> wrote:
> >
> > On Thu, Feb 13, 2020 at 11:58:39AM -0800, Darrick J. Wong wrote:
> > > On Thu, Feb 13, 2020 at 11:05:13AM -0800, Ira Weiny wrote:
> > > > On Thu, Feb 13, 2020 at 11:01:57AM -0800, 'Ira Weiny' wrote:
> > > > > On Wed, Feb 12, 2020 at 02:49:48PM -0500, Jeff Moyer wrote:
> > > > > > Ira Weiny <ira.weiny@intel.com> writes:
> > > > > >
> > > >
> > > > [snip]
> > > >
> > > > > > Given that we document the dax mount
> > > > > > option as "the way to get dax," it may be a good idea to allow for a
> > > > > > user to selectively disable dax, even when -o dax is specified. Is that
> > > > > > possible?
> > > > >
> > > > > Not with this patch set. And I'm not sure how that would work. The idea was
> > > > > that -o dax was simply an override for users who were used to having their
> > > > > entire FS be dax. We wanted to depreciate the use of "-o dax" in general. The
> > > > > individual settings are saved so I don't think it makes sense to ignore the -o
> > > > > dax in favor of those settings. Basically that would IMO make the -o dax
> > > > > useless.
> > > >
> > > > Oh and I forgot to mention that setting 'dax' on the root of the FS basically
> > > > provides '-o dax' functionality by default with the ability to "turn it off"
> > > > for files.
> > >
> > > Please don't further confuse FS_XFLAG_DAX and S_DAX.
> >
> > Yes... the above text is wrong WRT statx. But setting the physical
> > XFS_DIFLAG2_DAX flag on the root directory will by default cause all files and
> > directories created there to be XFS_DIFLAG2_DAX and so forth on down the tree
> > unless explicitly changed. This will be the same as mounting with '-o dax' but
> > with the ability to turn off dax for individual files. Which I think is the
> > functionality Jeff is wanting.
>
> To be clear you mean turn off XFS_DIFLAG2_DAX, not mask S_DAX when you
> say "turn off dax", right?
Yes.
[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.
[IF the underlying 'device' (superblock) does _not_ support DAX]
... S_DAX is _never_ set but the underlying XFS_DIFLAG2_DAX flags can be
toggled and will be inherited as above. Because S_DAX is never set access to
that file will be restricted to "not dax"...[1]
I could go into that level of detail in the doc if needed? I feel like we need
a more general name for XFS_DIFLAG2_DAX if I do.[2]
>
> The mount option simply forces "S_DAX" on all regular files as long as
> the underlying device (or soon to be superblock for virtiofs) supports
> it. There is no method to mask S_DAX when the filesystem was mounted
> with -o dax. Otherwise we would seem to need yet another physical flag
> to "always disable" dax.
Exactly. I don't think we want to support that. From this thread alone it
seems we have enough complexity and that would be another layer...
;-)
Ira
[1] I'm beginning to think that if I type dax one more time I'm going to go
crazy... :-P
[2] I have patches in the wings to introduce EXT4_DAX_FL as an ext4 on disk bit
which would be equivalent to XFS_DIFLAG2_DAX. If anyone wants a better name
let me know.
next prev parent reply other threads:[~2020-02-14 20:06 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-08 19:34 [PATCH v3 00/12] Enable per-file/directory DAX operations V3 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 [this message]
2020-02-14 21:23 ` Jeff Moyer
2020-02-14 21:58 ` Ira Weiny
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200214200607.GA18593@iweiny-DESK2.sc.intel.com \
--to=ira.weiny@intel.com \
--cc=dan.j.williams@intel.com \
--cc=darrick.wong@oracle.com \
--cc=david@fromorbit.com \
--cc=hch@lst.de \
--cc=jack@suse.cz \
--cc=jmoyer@redhat.com \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=tytso@mit.edu \
--cc=viro@zeniv.linux.org.uk \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).