From: Ira Weiny <ira.weiny@intel.com>
To: "Darrick J. Wong" <darrick.wong@oracle.com>
Cc: Dan Williams <dan.j.williams@intel.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Dave Chinner <david@fromorbit.com>,
Christoph Hellwig <hch@lst.de>,
"Theodore Y. Ts'o" <tytso@mit.edu>, Jan Kara <jack@suse.cz>,
Jeff Moyer <jmoyer@redhat.com>,
linux-ext4 <linux-ext4@vger.kernel.org>,
linux-xfs <linux-xfs@vger.kernel.org>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>
Subject: Re: [PATCH V7 9/9] Documentation/dax: Update Usage section
Date: Tue, 14 Apr 2020 13:00:15 -0700 [thread overview]
Message-ID: <20200414200015.GF1853609@iweiny-DESK2.sc.intel.com> (raw)
In-Reply-To: <20200414195754.GH6742@magnolia>
On Tue, Apr 14, 2020 at 12:57:54PM -0700, Darrick J. Wong wrote:
> On Tue, Apr 14, 2020 at 12:04:57PM -0700, Dan Williams wrote:
> > On Tue, Apr 14, 2020 at 9:15 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
[snip]
> > > > > +
> > > > > +Enabling DAX on xfs
> > > > > +-------------------
> > > > > +
> > > > > +Summary
> > > > > +-------
> > > > > +
> > > > > + 1. There exists an in-kernel access mode flag S_DAX that is set when
> > > > > + file accesses go directly to persistent memory, bypassing the page
> > > > > + cache.
> > > >
> > > > I had reserved some quibbling with this wording, but now that this is
> > > > being proposed as documentation I'll let my quibbling fly. "dax" may
> > > > imply, but does not require persistent memory nor does it necessarily
> > > > "bypass page cache". For example on configurations that support dax,
> > > > but turn off MAP_SYNC (like virtio-pmem), a software flush is
> > > > required. Instead, if we're going to define "dax" here I'd prefer it
> > > > be a #include of the man page definition that is careful (IIRC) to
> > > > only talk about semantics and not backend implementation details. In
> > > > other words, dax is to page-cache as direct-io is to page cache,
> > > > effectively not there, but dig a bit deeper and you may find it.
> > >
> > > Uh, which manpage? Are you talking about the MAP_SYNC documentation?
> >
> > No, I was referring to the proposed wording for STATX_ATTR_DAX.
> > There's no reason for this description to say anything divergent from
> > that description.
>
> Ahh, ok. Something like this, then:
>
> 1. There exists an in-kernel access mode flag S_DAX. When set, the
> file is in the DAX (cpu direct access) state. DAX state attempts to
> minimize software cache effects for both I/O and memory mappings of
> this file. The S_DAX state is exposed to userspace via the
> STATX_ATTR_DAX statx flag.
>
> See the STATX_ATTR_DAX in the statx(2) manpage for more information.
We crossed in the ether!!! I propose even less details here... Leave all the
details to the man page.
<quote>
1. There exists an in-kernel access mode flag S_DAX that is set when file
accesses is enabled for 'DAX'. Applications must call statx to discover
the current S_DAX state (STATX_ATTR_DAX). See the man page for statx for
more details.
</quote>
Ira
next prev parent reply other threads:[~2020-04-14 20:00 UTC|newest]
Thread overview: 47+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-13 5:40 [PATCH V7 0/9] Enable per-file/per-directory DAX operations V7 ira.weiny
2020-04-13 5:40 ` [PATCH V7 1/9] fs/xfs: Remove unnecessary initialization of i_rwsem ira.weiny
2020-04-13 15:41 ` Darrick J. Wong
2020-04-13 5:40 ` [PATCH V7 2/9] fs: Remove unneeded IS_DAX() check in io_is_direct() ira.weiny
2020-04-14 6:22 ` Christoph Hellwig
2020-04-13 5:40 ` [PATCH V7 3/9] fs/stat: Define DAX statx attribute ira.weiny
2020-04-14 6:23 ` Christoph Hellwig
2020-04-14 20:39 ` Ira Weiny
2020-04-13 5:40 ` [PATCH V7 4/9] fs/xfs: Make DAX mount option a tri-state ira.weiny
2020-04-13 15:46 ` Darrick J. Wong
2020-04-13 19:28 ` Ira Weiny
2020-04-14 6:24 ` Christoph Hellwig
2020-04-14 6:25 ` Christoph Hellwig
2020-04-14 20:34 ` Ira Weiny
2020-04-13 5:40 ` [PATCH V7 5/9] fs/xfs: Create function xfs_inode_enable_dax() ira.weiny
2020-04-13 15:52 ` Darrick J. Wong
2020-04-13 19:39 ` Ira Weiny
2020-04-14 6:27 ` Christoph Hellwig
2020-04-14 20:43 ` Ira Weiny
2020-04-13 5:40 ` [PATCH V7 6/9] fs/xfs: Combine xfs_diflags_to_linux() and xfs_diflags_to_iflags() ira.weiny
2020-04-13 16:01 ` Darrick J. Wong
2020-04-14 4:07 ` Ira Weiny
2020-04-13 5:40 ` [PATCH V7 7/9] fs: Define I_DONTCACNE in VFS layer ira.weiny
2020-04-13 16:09 ` Darrick J. Wong
2020-04-13 16:13 ` Darrick J. Wong
2020-04-13 19:44 ` Ira Weiny
2020-04-14 15:26 ` Jan Kara
2020-04-14 15:45 ` Ira Weiny
2020-04-14 15:59 ` Jan Kara
2020-04-13 5:40 ` [PATCH V7 8/9] fs/xfs: Change xfs_ioctl_setattr_dax_invalidate() ira.weiny
2020-04-13 16:12 ` Darrick J. Wong
2020-04-13 19:46 ` Ira Weiny
2020-04-13 5:40 ` [PATCH V7 9/9] Documentation/dax: Update Usage section ira.weiny
2020-04-13 16:19 ` Darrick J. Wong
2020-04-14 4:38 ` Ira Weiny
2020-04-14 5:12 ` Dan Williams
2020-04-14 19:48 ` Ira Weiny
2020-04-15 8:23 ` Jan Kara
2020-04-14 5:21 ` Dan Williams
2020-04-14 16:15 ` Darrick J. Wong
2020-04-14 19:04 ` Dan Williams
2020-04-14 19:57 ` Darrick J. Wong
2020-04-14 20:00 ` Ira Weiny [this message]
2020-04-14 20:18 ` Darrick J. Wong
2020-04-14 20:54 ` Ira Weiny
2020-04-14 21:02 ` Darrick J. Wong
2020-04-14 19:58 ` Ira Weiny
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