From: Dave Chinner <david@fromorbit.com>
To: Dan Williams <dan.j.williams@intel.com>
Cc: "Darrick J. Wong" <darrick.wong@oracle.com>,
Ira Weiny <ira.weiny@intel.com>, Jan Kara <jack@suse.cz>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
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: Sat, 18 Jan 2020 20:11:05 +1100 [thread overview]
Message-ID: <20200118091105.GA9407@dread.disaster.area> (raw)
In-Reply-To: <CAPcyv4jDMsPj_vZwDOgPkfHLELZWqeJugKgKNVKbpiZ9th683g@mail.gmail.com>
On Wed, Jan 15, 2020 at 10:05:00PM -0800, Dan Williams wrote:
> On Wed, Jan 15, 2020 at 9:39 PM Darrick J. Wong <darrick.wong@oracle.com> wrote:
> [..]
> > > 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...)
>
> Oh? That text was motivated by the open(2) man page description of O_SYNC.
Ugh. "synchronous I/O" means two different things, depending on
context. In the AIO context, it means "process context waits for operation
completion direct", but in the O_SYNC context, it means "we guarantee
data integrity for each I/O submitted".
Indeed, O_SYNC AIO is a thing. i.e. we can do an "async sync
write" to guarantee data integrity without directly waiting for
it. Now try describing that only using the words "synchronous
write" to describe both behaviours. :)
IOWs, if you are talking about data integrity, you need to
explicitly say "O_SYNC semantics", not "synchronous write", because
"synchronous write" is totally ambiguous without the O_SYNC context
of the open(2) man page...
Cheers,
Dave.
--
Dave Chinner
david@fromorbit.com
next prev parent reply other threads:[~2020-01-18 9:11 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
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 [this message]
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
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=20200118091105.GA9407@dread.disaster.area \
--to=david@fromorbit.com \
--cc=dan.j.williams@intel.com \
--cc=darrick.wong@oracle.com \
--cc=hch@lst.de \
--cc=ira.weiny@intel.com \
--cc=jack@suse.cz \
--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).