From: Trond Myklebust <trondmy@hammerspace.com>
To: "bfields@fieldses.org" <bfields@fieldses.org>,
"neilb@suse.de" <neilb@suse.de>
Cc: "zohar@linux.ibm.com" <zohar@linux.ibm.com>,
"djwong@kernel.org" <djwong@kernel.org>,
"xiubli@redhat.com" <xiubli@redhat.com>,
"brauner@kernel.org" <brauner@kernel.org>,
"linux-xfs@vger.kernel.org" <linux-xfs@vger.kernel.org>,
"linux-btrfs@vger.kernel.org" <linux-btrfs@vger.kernel.org>,
"linux-api@vger.kernel.org" <linux-api@vger.kernel.org>,
"david@fromorbit.com" <david@fromorbit.com>,
"fweimer@redhat.com" <fweimer@redhat.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"jlayton@kernel.org" <jlayton@kernel.org>,
"chuck.lever@oracle.com" <chuck.lever@oracle.com>,
"linux-man@vger.kernel.org" <linux-man@vger.kernel.org>,
"linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
"tytso@mit.edu" <tytso@mit.edu>,
"viro@zeniv.linux.org.uk" <viro@zeniv.linux.org.uk>,
"jack@suse.cz" <jack@suse.cz>,
"linux-ext4@vger.kernel.org" <linux-ext4@vger.kernel.org>,
"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
"adilger.kernel@dilger.ca" <adilger.kernel@dilger.ca>,
"lczerner@redhat.com" <lczerner@redhat.com>,
"ceph-devel@vger.kernel.org" <ceph-devel@vger.kernel.org>
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field
Date: Thu, 15 Sep 2022 15:08:34 +0000 [thread overview]
Message-ID: <577b6d8a7243aeee37eaa4bbb00c90799586bc48.camel@hammerspace.com> (raw)
In-Reply-To: <20220915140644.GA15754@fieldses.org>
On Thu, 2022-09-15 at 10:06 -0400, J. Bruce Fields wrote:
> On Tue, Sep 13, 2022 at 09:14:32AM +1000, NeilBrown wrote:
> > On Mon, 12 Sep 2022, J. Bruce Fields wrote:
> > > On Sun, Sep 11, 2022 at 08:13:11AM +1000, NeilBrown wrote:
> > > > On Fri, 09 Sep 2022, Jeff Layton wrote:
> > > > >
> > > > > The machine crashes and comes back up, and we get a query for
> > > > > i_version
> > > > > and it comes back as X. Fine, it's an old version. Now there
> > > > > is a write.
> > > > > What do we do to ensure that the new value doesn't collide
> > > > > with X+1?
> > > >
> > > > (I missed this bit in my earlier reply..)
> > > >
> > > > How is it "Fine" to see an old version?
> > > > The file could have changed without the version changing.
> > > > And I thought one of the goals of the crash-count was to be
> > > > able to
> > > > provide a monotonic change id.
> > >
> > > I was still mainly thinking about how to provide reliable close-
> > > to-open
> > > semantics between NFS clients. In the case the writer was an NFS
> > > client, it wasn't done writing (or it would have COMMITted), so
> > > those
> > > writes will come in and bump the change attribute soon, and as
> > > long as
> > > we avoid the small chance of reusing an old change attribute,
> > > we're OK,
> > > and I think it'd even still be OK to advertise
> > > CHANGE_TYPE_IS_MONOTONIC_INCR.
> >
> > You seem to be assuming that the client doesn't crash at the same
> > time
> > as the server (maybe they are both VMs on a host that lost
> > power...)
> >
> > If client A reads and caches, client B writes, the server crashes
> > after
> > writing some data (to already allocated space so no inode update
> > needed)
> > but before writing the new i_version, then client B crashes.
> > When server comes back the i_version will be unchanged but the data
> > has
> > changed. Client A will cache old data indefinitely...
>
> I guess I assume that if all we're promising is close-to-open, then a
> client isn't allowed to trust its cache in that situation. Maybe
> that's
> an overly draconian interpretation of close-to-open.
>
> Also, I'm trying to think about how to improve things incrementally.
> Incorporating something like a crash count into the on-disk i_version
> fixes some cases without introducing any new ones or regressing
> performance after a crash.
>
> If we subsequently wanted to close those remaining holes, I think
> we'd
> need the change attribute increment to be seen as atomic with respect
> to
> its associated change, both to clients and (separately) on disk.
> (That
> would still allow the change attribute to go backwards after a crash,
> to
> the value it held as of the on-disk state of the file. I think
> clients
> should be able to deal with that case.)
>
> But, I don't know, maybe a bigger hammer would be OK:
>
If you're not going to meet the minimum bar of data integrity, then
this whole exercise is just a massive waste of everyone's time. The
answer then going forward is just to recommend never using Linux as an
NFS server. Makes my life much easier, because I no longer have to
debug any of the issues.
>
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@hammerspace.com
next prev parent reply other threads:[~2022-09-15 15:15 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
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 [this message]
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
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=577b6d8a7243aeee37eaa4bbb00c90799586bc48.camel@hammerspace.com \
--to=trondmy@hammerspace.com \
--cc=adilger.kernel@dilger.ca \
--cc=bfields@fieldses.org \
--cc=brauner@kernel.org \
--cc=ceph-devel@vger.kernel.org \
--cc=chuck.lever@oracle.com \
--cc=david@fromorbit.com \
--cc=djwong@kernel.org \
--cc=fweimer@redhat.com \
--cc=jack@suse.cz \
--cc=jlayton@kernel.org \
--cc=lczerner@redhat.com \
--cc=linux-api@vger.kernel.org \
--cc=linux-btrfs@vger.kernel.org \
--cc=linux-ext4@vger.kernel.org \
--cc=linux-fsdevel@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux-man@vger.kernel.org \
--cc=linux-nfs@vger.kernel.org \
--cc=linux-xfs@vger.kernel.org \
--cc=neilb@suse.de \
--cc=tytso@mit.edu \
--cc=viro@zeniv.linux.org.uk \
--cc=xiubli@redhat.com \
--cc=zohar@linux.ibm.com \
/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).