From: "Darrick J. Wong" <darrick.wong@oracle.com>
To: Ira Weiny <ira.weiny@intel.com>
Cc: 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>,
Dave Chinner <david@fromorbit.com>,
Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute
Date: Wed, 15 Jan 2020 21:39:35 -0800 [thread overview]
Message-ID: <20200116053935.GB8235@magnolia> (raw)
In-Reply-To: <20200115223821.GG23311@iweiny-DESK2.sc.intel.com>
On Wed, Jan 15, 2020 at 02:38:21PM -0800, Ira Weiny wrote:
> On Wed, Jan 15, 2020 at 12:10:50PM -0800, Dan Williams wrote:
> > On Wed, Jan 15, 2020 at 11:45 AM Ira Weiny <ira.weiny@intel.com> wrote:
> > >
> > > On Wed, Jan 15, 2020 at 09:38:34AM -0800, Darrick J. Wong wrote:
> > > > On Wed, Jan 15, 2020 at 12:37:15PM +0100, Jan Kara wrote:
> > > > > On Fri 10-01-20 11:29:31, ira.weiny@intel.com wrote:
> > > > > > From: Ira Weiny <ira.weiny@intel.com>
> > > > > >
>
> [snip]
>
> > > Ok I changed a couple of things as well. How does this sound?
> > >
> > >
> > > STATX_ATTR_DAX
> > >
> > > DAX (cpu direct access) is a file mode that attempts to minimize
> >
> > s/mode/state/?
>
> DOH! yes state... ;-)
>
> >
> > > software cache effects for both I/O and memory mappings of this
> > > file. It requires a block device and file system which have
> > > been configured to support DAX.
> >
> > It may not require a block device in the future.
>
> Ok:
>
> "It requires a file system which has been configured to support DAX." ?
>
> I'm trying to separate the user of the individual STATX DAX flag from the Admin
> details of configuring the file system and/or devices which supports it.
>
> Also, I just realized that we should follow the format of the other STATX_*
> attributes. They all read something like "the file is..."
>
> So I'm adding that text as well.
>
> >
> > >
> > > DAX generally assumes all accesses are via cpu load / store
> > > instructions which can minimize overhead for small accesses, but
> > > may adversely affect cpu utilization for large transfers.
> > >
> > > File I/O is done directly to/from user-space buffers and memory
> > > mapped I/O may be performed with direct memory mappings that
> > > bypass kernel page cache.
> > >
> > > While the DAX property tends to result in data being transferred
> > > synchronously, it does not give the same guarantees of
> > > synchronous I/O where data and the necessary metadata are
> >
> > Maybe use "O_SYNC I/O" explicitly to further differentiate the 2
> > meanings of "synchronous" in this sentence?
>
> Done.
>
> >
> > > transferred together.
> > >
> > > A DAX file may support being mapped with the MAP_SYNC flag,
> > > which enables a program to use CPU cache flush operations to
> >
> > s/operations/instructions/
>
> Done.
>
> >
> > > persist CPU store operations without an explicit fsync(2). See
> > > mmap(2) for more information.
> >
> > I think this also wants a reference to the Linux interpretation of
> > platform "persistence domains" we were discussing that here [1], but
> > maybe it should be part of a "pmem" manpage that can be referenced
> > from this man page.
>
> Sure, but for now I think referencing mmap for details on MAP_SYNC works.
>
> I suspect that we may have some word smithing once I get this series in and we
> submit a change to the statx man page itself. Can I move forward with the
> following for this patch?
>
> <quote>
> STATX_ATTR_DAX
>
> The file is in the DAX (cpu direct access) state. DAX state
Hmm, now that I see it written out, I <cough> kind of like "DAX mode"
better now. :/
"The file is in DAX (CPU direct access) mode. DAX mode attempts..."
> attempts to minimize software cache effects for both I/O and
> memory mappings of this file. It requires a file system which
> has been configured to support DAX.
>
> DAX generally assumes all accesses are via cpu load / store
> instructions which can minimize overhead for small accesses, but
> may adversely affect cpu utilization for large transfers.
>
> File I/O is done directly to/from user-space buffers and memory
> mapped I/O may be performed with direct memory mappings that
> bypass kernel page cache.
>
> While the DAX property tends to result in data being transferred
> synchronously, it does not give the same guarantees of
> synchronous I/O where data and the necessary metadata are
> transferred together.
(I'm frankly not sure that synchronous I/O actually guarantees that the
metadata has hit stable storage...)
--D
> A DAX file may support being mapped with the MAP_SYNC flag,
> which enables a program to use CPU cache flush instructions to
> persist CPU store operations without an explicit fsync(2). See
> mmap(2) for more information.
> </quote>
>
> Ira
>
> >
> > [1]: http://lore.kernel.org/r/20200108064905.170394-1-aneesh.kumar@linux.ibm.com
next prev parent reply other threads:[~2020-01-16 5:40 UTC|newest]
Thread overview: 55+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-10 19:29 [RFC PATCH V2 00/12] Enable per-file/directory DAX operations V2 ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 01/12] fs/stat: Define DAX statx attribute ira.weiny
2020-01-15 11:37 ` Jan Kara
2020-01-15 17:38 ` Darrick J. Wong
2020-01-15 19:45 ` Ira Weiny
2020-01-15 20:10 ` Dan Williams
2020-01-15 22:38 ` Ira Weiny
2020-01-16 5:39 ` Darrick J. Wong [this message]
2020-01-16 6:05 ` Dan Williams
2020-01-16 6:18 ` Darrick J. Wong
2020-01-16 6:25 ` Dan Williams
2020-01-18 9:11 ` Dave Chinner
2020-01-16 17:55 ` Ira Weiny
2020-01-16 18:04 ` Darrick J. Wong
2020-01-16 18:52 ` Ira Weiny
2020-01-16 22:19 ` Darrick J. Wong
2020-01-17 11:58 ` Jan Kara
2020-01-10 19:29 ` [RFC PATCH V2 02/12] fs/xfs: Isolate the physical DAX flag from effective ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 03/12] fs/xfs: Separate functionality of xfs_inode_supports_dax() ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 04/12] fs/xfs: Clean up DAX support check ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 05/12] fs: remove unneeded IS_DAX() check ira.weiny
2020-01-16 9:38 ` Jan Kara
2020-01-16 18:47 ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 06/12] fs/xfs: Check if the inode supports DAX under lock ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 07/12] fs: Add locking for a dynamic inode 'mode' ira.weiny
2020-01-13 22:12 ` Darrick J. Wong
2020-01-14 0:20 ` Ira Weiny
2020-01-14 1:03 ` Darrick J. Wong
2020-01-15 19:08 ` Ira Weiny
2020-01-16 5:40 ` Darrick J. Wong
2020-01-16 18:54 ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 08/12] fs/xfs: Add lock/unlock mode to xfs ira.weiny
2020-01-13 22:19 ` Darrick J. Wong
2020-01-14 0:35 ` Ira Weiny
2020-01-15 0:57 ` Ira Weiny
2020-01-15 23:52 ` Ira Weiny
2020-01-16 9:24 ` Jan Kara
2020-01-16 19:12 ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 09/12] fs: Prevent mode change if file is mmap'ed ira.weiny
2020-01-13 22:22 ` Darrick J. Wong
2020-01-14 0:46 ` Ira Weiny
2020-01-14 1:30 ` Darrick J. Wong
2020-01-14 17:53 ` Ira Weiny
2020-01-15 11:34 ` Jan Kara
2020-01-15 18:24 ` Ira Weiny
2020-01-15 10:21 ` David Laight
2020-01-15 17:53 ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 10/12] fs/xfs: Fix truncate up ira.weiny
2020-01-13 22:27 ` Darrick J. Wong
2020-01-14 0:40 ` Ira Weiny
2020-01-14 1:14 ` Darrick J. Wong
2020-01-14 19:00 ` Ira Weiny
2020-01-14 19:39 ` Ira Weiny
2020-01-10 19:29 ` [RFC PATCH V2 11/12] fs/xfs: Clean up locking in dax invalidate ira.weiny
2020-01-10 19:29 ` [RFC PATCH V2 12/12] fs/xfs: Allow toggle of effective DAX flag ira.weiny
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