From: "Frank Filz" <ffilzlnx@mindspring.com>
To: "'Jeff Layton'" <jlayton@kernel.org>,
"'Trond Myklebust'" <trondmy@hammerspace.com>, <jack@suse.cz>
Cc: <zohar@linux.ibm.com>, <djwong@kernel.org>, <brauner@kernel.org>,
<linux-xfs@vger.kernel.org>, <bfields@fieldses.org>,
<linux-api@vger.kernel.org>, <neilb@suse.de>,
<david@fromorbit.com>, <fweimer@redhat.com>,
<linux-kernel@vger.kernel.org>, <chuck.lever@oracle.com>,
<linux-man@vger.kernel.org>, <linux-nfs@vger.kernel.org>,
<linux-ext4@vger.kernel.org>, <tytso@mit.edu>,
<viro@zeniv.linux.org.uk>, <xiubli@redhat.com>,
<linux-fsdevel@vger.kernel.org>, <adilger.kernel@dilger.ca>,
<lczerner@redhat.com>, <ceph-devel@vger.kernel.org>,
<linux-btrfs@vger.kernel.org>
Subject: RE: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO_VERSION field
Date: Fri, 23 Sep 2022 07:58:55 -0700 [thread overview]
Message-ID: <01ae01d8cf5d$023474d0$069d5e70$@mindspring.com> (raw)
In-Reply-To: <baf852dfb57aaf5a670bc88236f8d62c99668fcc.camel@kernel.org>
> -----Original Message-----
> From: Jeff Layton [mailto:jlayton@kernel.org]
> Sent: Friday, September 23, 2022 6:50 AM
> To: Trond Myklebust <trondmy@hammerspace.com>; jack@suse.cz
> Cc: zohar@linux.ibm.com; djwong@kernel.org; brauner@kernel.org; linux-
> xfs@vger.kernel.org; bfields@fieldses.org; linux-api@vger.kernel.org;
> neilb@suse.de; david@fromorbit.com; fweimer@redhat.com; linux-
> kernel@vger.kernel.org; chuck.lever@oracle.com; linux-man@vger.kernel.org;
> linux-nfs@vger.kernel.org; linux-ext4@vger.kernel.org; tytso@mit.edu;
> viro@zeniv.linux.org.uk; xiubli@redhat.com; linux-fsdevel@vger.kernel.org;
> adilger.kernel@dilger.ca; lczerner@redhat.com; ceph-devel@vger.kernel.org;
> linux-btrfs@vger.kernel.org
> Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
> STATX_INO_VERSION field
>
> On Fri, 2022-09-23 at 13:44 +0000, Trond Myklebust wrote:
> > On Fri, 2022-09-23 at 11:56 +0200, Jan Kara wrote:
> > > On Thu 22-09-22 16:18:02, Jeff Layton wrote:
> > > > On Thu, 2022-09-22 at 06:18 -0400, Jeff Layton wrote:
> > > > > On Thu, 2022-09-22 at 07:41 +1000, Dave Chinner wrote:
> > > > > > e.g. The NFS server can track the i_version values when the
> > > > > > NFSD syncs/commits a given inode. The nfsd can sample
> > > > > > i_version it when calls ->commit_metadata or flushed data on
> > > > > > the inode, and then when it peeks at i_version when gathering
> > > > > > post-op attrs (or any other getattr op) it can decide that
> > > > > > there is too much in-memory change (e.g. 10,000 counts since
> > > > > > last sync) and sync the inode.
> > > > > >
> > > > > > i.e. the NFS server can trivially cap the maximum number of
> > > > > > uncommitted NFS change attr bumps it allows to build up in
> > > > > > memory.
> > > > > > At that point, the NFS server has a bound "maximum write count"
> > > > > > that
> > > > > > can be used in conjunction with the xattr based crash counter
> > > > > > to determine how the change_attr is bumped by the crash
> > > > > > counter.
> > > > >
> > > > > Well, not "trivially". This is the bit where we have to grow
> > > > > struct inode (or the fs-specific inode), as we'll need to know
> > > > > what the latest on-disk value is for the inode.
> > > > >
> > > > > I'm leaning toward doing this on the query side. Basically, when
> > > > > nfsd goes to query the i_version, it'll check the delta between
> > > > > the current version and the latest one on disk. If it's bigger
> > > > > than X then we'd just return NFS4ERR_DELAY to the client.
> > > > >
> > > > > If the delta is >X/2, maybe it can kick off a workqueue job or
> > > > > something that calls write_inode with WB_SYNC_ALL to try to get
> > > > > the thing onto the platter ASAP.
> > > >
> > > > Still looking at this bit too. Probably we can just kick off a
> > > > WB_SYNC_NONE filemap_fdatawrite at that point and hope for the
> > > > best?
> > >
> > > "Hope" is not a great assurance regarding data integrity ;) Anyway,
> > > it depends on how you imagine the "i_version on disk" is going to be
> > > maintained. It could be maintained by NFSD inside
> > > commit_inode_metadata() -
> > > fetch current i_version value before asking filesystem for the sync
> > > and by the time commit_metadata() returns we know that value is on
> > > disk. If we detect the current - on_disk is > X/2, we call
> > > commit_inode_metadata() and we are done. It is not even *that*
> > > expensive because usually filesystems optimize away unnecessary IO
> > > when the inode didn't change since last time it got synced.
> > >
> >
> > Note that these approaches requiring 3rd party help in order to track
> > i_version integrity across filesystem crashes all make the idea of
> > adding i_version to statx() a no-go.
> >
> > It is one thing for knfsd to add specialised machinery for integrity
> > checking, but if all applications need to do so, then they are highly
> > unlikely to want to adopt this attribute.
> >
> >
>
> Absolutely. That is the downside of this approach, but the priority here
has
> always been to improve nfsd. If we don't get the ability to present this
info via
> statx, then so be it. Later on, I suppose we can move that handling into
the
> kernel in some fashion if we decide it's worthwhile.
>
> That said, not having this in statx makes it more difficult to test
i_version
> behavior. Maybe we can add a generic ioctl for that in the interim?
Having i_version in statx would be really nice for nfs-ganesha. I would
consider doing the extra integrity stuff or we may in some cases be able to
rely on the filesystem, but in any case, i_version would be an improvement
over using ctime or mtime for a change attribute.
Frank
next prev parent reply other threads:[~2022-09-23 15:05 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
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 [this message]
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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