From: Ira Weiny <ira.weiny@intel.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>,
Dave Chinner <david@fromorbit.com>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
Dan Williams <dan.j.williams@intel.com>, Jan Kara <jack@suse.cz>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5
Date: Thu, 2 Apr 2020 21:39:01 -0700 [thread overview]
Message-ID: <20200403043901.GH3952565@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200401040021.GC56958@magnolia>
On Wed, Apr 01, 2020 at 04:00:21AM +0000, Darrick J. Wong wrote:
> On Mon, Mar 16, 2020 at 10:55:09AM +0100, Christoph Hellwig wrote:
> > On Mon, Mar 16, 2020 at 10:52:24AM +0100, Jan Kara wrote:
> > > > This sounds reasonable to me.
> > > >
> > > > As for deprecating the mount option, I think at a minimum it needs to
> > > > continue be accepted as an option even if it is ignored to not break
> > > > existing setups.
> > >
> > > Agreed. But that's how we usually deprecate mount options. Also I'd say
> > > that statx() support for reporting DAX state and some education of
> > > programmers using DAX is required before we deprecate the mount option
> > > since currently applications check 'dax' mount option to determine how much
> > > memory they need to set aside for page cache before they consume everything
> > > else on the machine...
> >
> > I don't even think we should deprecate it. It isn't painful to maintain
> > and actually useful for testing. Instead we should expand it into a
> > tristate:
> >
> > dax=off
> > dax=flag
> > dax=always
> >
> > where the existing "dax" option maps to "dax=always" and nodax maps
> > to "dax=off". and dax=flag becomes the default for DAX capable devices.
>
> That works for me. In summary:
>
> - Applications must call statx to discover the current S_DAX state.
>
> - There exists an advisory file inode flag FS_XFLAG_DAX that can be
> changed on files that have no blocks allocated to them. Changing
> this flag does not necessarily change the S_DAX state immediately
> but programs can query the S_DAX state via statx.
>
> If FS_XFLAG_DAX is set and the fs is on pmem then it will always
> enable S_DAX at inode load time; if FS_XFLAG_DAX is not set, it will
> never enable S_DAX. Unless overridden...
>
> - There exists a dax= mount option. dax=off means "never set S_DAX,
> ignore FS_XFLAG_DAX"; dax=always means "always set S_DAX (at least on
> pmem), ignore FS_XFLAG_DAX"; and dax=iflag means "follow FS_XFLAG_DAX"
> and is the default. "dax" by itself means "dax=always". "nodax"
> means "dax=off".
>
> - There exists an advisory directory inode flag FS_XFLAG_DAX that can
> be changed at any time. The flag state is copied into any files or
> subdirectories created within that directory. If programs require
> that file access runs in S_DAX mode, they'll have to create those
> files themselves inside a directory with FS_XFLAG_DAX set, or mount
> the fs with dax=always.
One other thing to add here. They _can_ set the FS_XFLAG_DAX on a file with
data and force an eviction to get S_DAX to change.
I think that is a nice reason to have a different error code returned.
>
> Ok? Let's please get this part finished for 5.8, then we can get back
> to arguing about fs-rmap and reflink and dax and whatnot.
I'm happy to see you motivated to get this in.
I'm starting with a new xfstest to make sure we agree on the semantics prior to
more patches. I hope to have the xfstest patch sent tomorrow sometime.
Ira
>
> --D
next prev parent reply other threads:[~2020-04-03 4:39 UTC|newest]
Thread overview: 45+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 5:24 [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5 ira.weiny
2020-02-27 5:24 ` [PATCH V5 01/12] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny
2020-02-27 17:25 ` Ira Weiny
2020-02-27 5:24 ` [PATCH V5 02/12] fs: Remove unneeded IS_DAX() check ira.weiny
2020-02-27 5:24 ` [PATCH V5 03/12] fs/stat: Define DAX statx attribute ira.weiny
2020-02-27 5:24 ` [PATCH V5 04/12] fs/xfs: Isolate the physical DAX flag from enabled ira.weiny
2020-02-27 5:24 ` [PATCH V5 05/12] fs/xfs: Create function xfs_inode_enable_dax() ira.weiny
2020-03-01 22:37 ` Dave Chinner
2020-02-27 5:24 ` [PATCH V5 06/12] fs: Add locking for a dynamic address space operations state ira.weiny
2020-03-02 1:26 ` Dave Chinner
2020-03-02 1:36 ` Dave Chinner
2020-02-27 5:24 ` [PATCH V5 07/12] fs: Prevent DAX state change if file is mmap'ed ira.weiny
2020-02-27 5:24 ` [PATCH V5 08/12] fs/xfs: Hold off aops users while changing DAX state ira.weiny
2020-02-27 5:24 ` [PATCH V5 09/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-02-27 5:24 ` [PATCH V5 10/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny
2020-02-27 5:24 ` [PATCH V5 11/12] fs/xfs: Remove xfs_diflags_to_linux() ira.weiny
2020-02-27 5:24 ` [PATCH V5 12/12] Documentation/dax: Update Usage section ira.weiny
2020-03-05 15:51 ` [PATCH V5 00/12] Enable per-file/per-directory DAX operations V5 Christoph Hellwig
2020-03-09 17:04 ` Ira Weiny
2020-03-11 3:36 ` Darrick J. Wong
2020-03-11 6:29 ` Christoph Hellwig
2020-03-11 17:07 ` Dan Williams
2020-03-16 9:52 ` Jan Kara
2020-03-16 9:55 ` Christoph Hellwig
2020-04-01 4:00 ` Darrick J. Wong
2020-04-01 10:25 ` Jan Kara
2020-04-02 8:53 ` Christoph Hellwig
2020-04-02 20:55 ` Ira Weiny
2020-04-03 7:27 ` Christoph Hellwig
2020-04-03 15:48 ` Ira Weiny
2020-04-03 17:03 ` Jan Kara
2020-04-03 18:18 ` Ira Weiny
2020-04-03 18:21 ` Ira Weiny
2020-04-03 18:37 ` Darrick J. Wong
2020-04-05 6:19 ` Ira Weiny
2020-04-06 10:00 ` Jan Kara
2020-04-03 18:29 ` Darrick J. Wong
2020-04-03 16:05 ` Darrick J. Wong
2020-04-03 4:39 ` Ira Weiny [this message]
2020-03-11 6:39 ` Dave Chinner
2020-03-11 6:44 ` Christoph Hellwig
2020-03-11 17:07 ` Dan Williams
2020-03-12 0:49 ` Dave Chinner
2020-03-12 3:00 ` Darrick J. Wong
2020-03-12 7:27 ` Christoph Hellwig
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