From: Jeff Layton <jlayton@kernel.org>
To: "J. Bruce Fields" <bfields@fieldses.org>
Cc: NeilBrown <neilb@suse.de>,
tytso@mit.edu, adilger.kernel@dilger.ca, djwong@kernel.org,
david@fromorbit.com, trondmy@hammerspace.com,
viro@zeniv.linux.org.uk, zohar@linux.ibm.com, xiubli@redhat.com,
chuck.lever@oracle.com, lczerner@redhat.com, jack@suse.cz,
brauner@kernel.org, fweimer@redhat.com,
linux-man@vger.kernel.org, linux-api@vger.kernel.org,
linux-btrfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
linux-kernel@vger.kernel.org, ceph-devel@vger.kernel.org,
linux-ext4@vger.kernel.org, linux-nfs@vger.kernel.org,
linux-xfs@vger.kernel.org
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field
Date: Wed, 07 Sep 2022 09:12:34 -0400 [thread overview]
Message-ID: <771650a814ab1ff4dc5473d679936b747d9b6cf5.camel@kernel.org> (raw)
In-Reply-To: <20220907125211.GB17729@fieldses.org>
On Wed, 2022-09-07 at 08:52 -0400, J. Bruce Fields wrote:
> On Wed, Sep 07, 2022 at 08:47:20AM -0400, Jeff Layton wrote:
> > On Wed, 2022-09-07 at 21:37 +1000, NeilBrown wrote:
> > > On Wed, 07 Sep 2022, Jeff Layton wrote:
> > > > +The change to \fIstatx.stx_ino_version\fP is not atomic with respect to the
> > > > +other changes in the inode. On a write, for instance, the i_version it usually
> > > > +incremented before the data is copied into the pagecache. Therefore it is
> > > > +possible to see a new i_version value while a read still shows the old data.
> > >
> > > Doesn't that make the value useless?
> > >
> >
> > No, I don't think so. It's only really useful for comparing to an older
> > sample anyway. If you do "statx; read; statx" and the value hasn't
> > changed, then you know that things are stable.
>
> I don't see how that helps. It's still possible to get:
>
> reader writer
> ------ ------
> i_version++
> statx
> read
> statx
> update page cache
>
> right?
>
Yeah, I suppose so -- the statx wouldn't necessitate any locking. In
that case, maybe this is useless then other than for testing purposes
and userland NFS servers.
Would it be better to not consume a statx field with this if so? What
could we use as an alternate interface? ioctl? Some sort of global
virtual xattr? It does need to be something per-inode.
> >
> > > Surely the change number must
> > > change no sooner than the change itself is visible, otherwise stale data
> > > could be cached indefinitely.
> > >
> > > If currently implementations behave this way, surely they are broken.
> >
> > It's certainly not ideal but we've never been able to offer truly atomic
> > behavior here given that Linux is a general-purpose OS. The behavior is
> > a little inconsistent too:
> >
> > The c/mtime update and i_version bump on directories (mostly) occur
> > after the operation. c/mtime updates for files however are mostly driven
> > by calls to file_update_time, which happens before data is copied to the
> > pagecache.
> >
> > It's not clear to me why it's done this way. Maybe to ensure that the
> > metadata is up to date in the event that a statx comes in? Improving
> > this would be nice, but I don't see a way to do that without regressing
> > performance.
> > --
> > Jeff Layton <jlayton@kernel.org>
--
Jeff Layton <jlayton@kernel.org>
next prev parent reply other threads:[~2022-09-07 13:12 UTC|newest]
Thread overview: 126+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-07 11:16 [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field Jeff Layton
2022-09-07 11:37 ` NeilBrown
2022-09-07 12:20 ` J. Bruce Fields
2022-09-07 12:58 ` Jeff Layton
2022-09-07 12:47 ` Jeff Layton
2022-09-07 12:52 ` J. Bruce Fields
2022-09-07 13:12 ` Jeff Layton [this message]
2022-09-07 13:51 ` Jan Kara
2022-09-07 14:43 ` Jeff Layton
2022-09-08 0:44 ` NeilBrown
2022-09-08 8:33 ` Jan Kara
2022-09-08 15:21 ` Theodore Ts'o
2022-09-08 15:44 ` J. Bruce Fields
2022-09-08 15:44 ` Jeff Layton
2022-09-08 15:56 ` J. Bruce Fields
2022-09-08 16:15 ` Chuck Lever III
2022-09-08 17:40 ` Jeff Layton
2022-09-08 18:22 ` J. Bruce Fields
2022-09-08 19:07 ` Jeff Layton
2022-09-08 23:01 ` NeilBrown
2022-09-08 23:23 ` Jeff Layton
2022-09-08 23:45 ` NeilBrown
2022-09-09 15:45 ` J. Bruce Fields
2022-09-09 16:36 ` Jeff Layton
2022-09-10 14:56 ` J. Bruce Fields
2022-09-12 11:42 ` Jeff Layton
2022-09-12 12:13 ` Florian Weimer
2022-09-12 12:55 ` Jeff Layton
2022-09-12 13:20 ` Florian Weimer
2022-09-12 13:49 ` Jeff Layton
2022-09-12 13:51 ` J. Bruce Fields
2022-09-12 14:02 ` Jeff Layton
2022-09-12 14:47 ` J. Bruce Fields
2022-09-12 14:15 ` Trond Myklebust
2022-09-12 14:50 ` J. Bruce Fields
2022-09-12 14:56 ` Trond Myklebust
2022-09-12 15:32 ` Trond Myklebust
2022-09-12 15:49 ` Jeff Layton
2022-09-12 12:54 ` J. Bruce Fields
2022-09-12 12:59 ` Jeff Layton
2022-09-13 0:29 ` John Stoffel
2022-09-13 0:41 ` Dave Chinner
2022-09-13 1:49 ` NeilBrown
2022-09-13 2:41 ` Dave Chinner
2022-09-13 3:30 ` NeilBrown
2022-09-13 9:38 ` Theodore Ts'o
2022-09-13 19:02 ` J. Bruce Fields
2022-09-13 23:19 ` NeilBrown
2022-09-14 0:08 ` J. Bruce Fields
2022-09-09 20:34 ` John Stoffel
2022-09-10 22:13 ` NeilBrown
2022-09-12 10:43 ` Jeff Layton
2022-09-12 13:42 ` J. Bruce Fields
2022-09-12 23:14 ` NeilBrown
2022-09-15 14:06 ` J. Bruce Fields
2022-09-15 15:08 ` Trond Myklebust
2022-09-15 16:45 ` Jeff Layton
2022-09-15 17:49 ` Trond Myklebust
2022-09-15 18:11 ` Jeff Layton
2022-09-15 19:03 ` Trond Myklebust
2022-09-15 19:25 ` Jeff Layton
2022-09-15 22:23 ` NeilBrown
2022-09-16 6:54 ` Theodore Ts'o
2022-09-16 11:36 ` Jeff Layton
2022-09-16 15:11 ` Jeff Layton
2022-09-18 23:53 ` Dave Chinner
2022-09-19 13:13 ` Jeff Layton
2022-09-20 0:16 ` Dave Chinner
2022-09-20 10:26 ` Jeff Layton
2022-09-21 0:00 ` Dave Chinner
2022-09-21 10:33 ` Jeff Layton
2022-09-21 21:41 ` Dave Chinner
2022-09-22 10:18 ` Jeff Layton
2022-09-22 20:18 ` Jeff Layton
2022-09-23 9:56 ` Jan Kara
2022-09-23 10:19 ` Jeff Layton
2022-09-23 13:44 ` Trond Myklebust
2022-09-23 13:50 ` Jeff Layton
2022-09-23 14:58 ` Frank Filz
2022-09-26 22:43 ` NeilBrown
2022-09-27 11:14 ` Jeff Layton
2022-09-27 13:18 ` Jeff Layton
2022-09-15 15:41 ` Jeff Layton
2022-09-15 22:42 ` NeilBrown
2022-09-16 11:32 ` Jeff Layton
2022-09-09 12:11 ` Theodore Ts'o
2022-09-09 12:47 ` Jeff Layton
2022-09-09 13:48 ` Theodore Ts'o
2022-09-09 14:43 ` Jeff Layton
2022-09-09 14:58 ` Theodore Ts'o
2022-09-08 22:55 ` NeilBrown
2022-09-08 23:59 ` Trond Myklebust
2022-09-09 0:51 ` NeilBrown
2022-09-09 1:05 ` Trond Myklebust
2022-09-09 1:07 ` NeilBrown
2022-09-09 1:10 ` Trond Myklebust
2022-09-09 2:14 ` Trond Myklebust
2022-09-09 6:41 ` NeilBrown
2022-09-10 12:39 ` Jeff Layton
2022-09-10 22:53 ` NeilBrown
2022-09-12 10:25 ` Jeff Layton
2022-09-12 23:29 ` NeilBrown
2022-09-13 1:15 ` Dave Chinner
2022-09-13 1:41 ` NeilBrown
2022-09-13 19:01 ` Jeff Layton
2022-09-13 23:24 ` NeilBrown
2022-09-14 11:51 ` Jeff Layton
2022-09-14 22:45 ` NeilBrown
2022-09-14 23:02 ` NeilBrown
2022-09-08 22:40 ` NeilBrown
2022-09-07 13:55 ` Trond Myklebust
2022-09-07 14:05 ` Jeff Layton
2022-09-07 15:04 ` Trond Myklebust
2022-09-07 15:11 ` Jeff Layton
2022-09-08 0:40 ` NeilBrown
2022-09-08 11:34 ` Jeff Layton
2022-09-08 22:29 ` NeilBrown
2022-09-09 11:53 ` Jeff Layton
2022-09-10 22:58 ` NeilBrown
2022-09-10 19:46 ` Al Viro
2022-09-10 23:00 ` NeilBrown
2022-09-08 0:31 ` NeilBrown
2022-09-08 0:41 ` Trond Myklebust
2022-09-08 0:53 ` NeilBrown
2022-09-08 11:37 ` Jeff Layton
2022-09-08 12:40 ` Trond Myklebust
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