From: Ira Weiny <email@example.com> To: Dan Williams <firstname.lastname@example.org> Cc: "Darrick J. Wong" <email@example.com>, Jeff Moyer <firstname.lastname@example.org>, Linux Kernel Mailing List <email@example.com>, Alexander Viro <firstname.lastname@example.org>, Dave Chinner <email@example.com>, Christoph Hellwig <firstname.lastname@example.org>, "Theodore Y. Ts'o" <email@example.com>, Jan Kara <firstname.lastname@example.org>, linux-ext4 <email@example.com>, linux-xfs <firstname.lastname@example.org>, linux-fsdevel <email@example.com> Subject: Re: [PATCH v3 00/12] Enable per-file/directory DAX operations V3 Date: Fri, 14 Feb 2020 12:06:07 -0800 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 <firstname.lastname@example.org> 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 <email@example.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"... 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. > > 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  I'm beginning to think that if I type dax one more time I'm going to go crazy... :-P  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 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 [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
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