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From: "J. Bruce Fields" <bfields@fieldses.org>
To: Christoph Hellwig <hch@infradead.org>
Cc: Jeff Layton <jlayton@redhat.com>,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-nfs@vger.kernel.org, linux-ext4@vger.kernel.org,
	linux-btrfs@vger.kernel.org, linux-xfs@vger.kernel.org
Subject: Re: [RFC PATCH v1 00/30] fs: inode->i_version rework and optimization
Date: Tue, 21 Mar 2017 12:30:11 -0400	[thread overview]
Message-ID: <20170321163011.GA16666@fieldses.org> (raw)
In-Reply-To: <20170321134500.GA1318@infradead.org>

On Tue, Mar 21, 2017 at 06:45:00AM -0700, Christoph Hellwig wrote:
> On Mon, Mar 20, 2017 at 05:43:27PM -0400, J. Bruce Fields wrote:
> > To me, the interesting question is whether this allows us to turn on
> > i_version updates by default on xfs and ext4.
> 
> XFS v5 file systems have it on by default.

Great, thanks.

> Although we'll still need to agree on the exact semantics of i_version
> before it's going to be useful.

Once it's figured out maybe we should write it up for a manpage that
could be used if statx starts exposing it to userspace.

A first attempt:

- It's a u64.

- It works for regular files and directories.  (What about symlinks or
  other special types?)

- It changes between two checks if and only if there were intervening
  data or metadata changes.  The change will always be an increase, but
  the amount of the increase is meaningless.
	- NFS doesn't actually require that it increases, but I think it
	  should.  I assume 64 bits means we don't need a discussion of
	  wraparound.
	- AFS wants an actual counter: if you get i_version X, then
	  write twice, then get i_version X+2, you're allowed to assume
	  your writes were the only modifications.  Let's ignore this
	  for now.  In the future if someone explains how to count
	  operations, then we can extend the interface to tell the
	  caller it can get those extra semantics.

- It's durable; the above comparison still works if there were reboots
  between the two i_version checks.
	- I don't know how realistic this is--we may need to figure out
	  if there's a weaker guarantee that's still useful.  Do
	  filesystems actually make ctime/mtime/i_version changes
	  atomically with the changes that caused them?  What if a
	  change attribute is exposed to an NFS client but doesn't make
	  it to disk, and then that value is reused after reboot?

Am I missing any issues?

--b.

  reply	other threads:[~2017-03-21 16:31 UTC|newest]

Thread overview: 87+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-12-21 17:03 Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 01/30] lustre: don't set f_version in ll_readdir Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 02/30] ecryptfs: remove unnecessary i_version bump Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 03/30] ceph: remove the bump of i_version Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 04/30] f2fs: don't bother setting i_version Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 05/30] hpfs: don't bother with the i_version counter Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 06/30] jfs: remove initialization of " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 07/30] nilfs2: remove inode->i_version initialization Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 08/30] orangefs: remove initialization of i_version Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 09/30] reiserfs: remove unneeded i_version bump Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 10/30] ntfs: remove i_version handling Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 11/30] fs: new API for handling i_version Jeff Layton
2017-03-03 22:36   ` J. Bruce Fields
2017-03-04  0:09     ` Jeff Layton
2017-03-03 23:55   ` NeilBrown
2017-03-04  1:58     ` Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 12/30] fat: convert to new i_version API Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 13/30] affs: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 14/30] afs: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 15/30] btrfs: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 16/30] exofs: switch " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 17/30] ext2: convert " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 18/30] ext4: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 19/30] nfs: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 20/30] nfsd: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 21/30] ocfs2: " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 22/30] ufs: use " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 23/30] xfs: convert to " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 24/30] IMA: switch IMA over " Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 25/30] fs: add a "force" parameter to inode_inc_iversion Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 26/30] fs: only set S_VERSION when updating times if it has been queried Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 27/30] xfs: avoid setting XFS_ILOG_CORE if i_version doesn't need incrementing Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 28/30] btrfs: only dirty the inode in btrfs_update_time if something was changed Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 29/30] fs: track whether the i_version has been queried with an i_state flag Jeff Layton
2017-03-04  0:03   ` NeilBrown
2017-03-04  0:43     ` Jeff Layton
2016-12-21 17:03 ` [RFC PATCH v1 30/30] fs: convert i_version counter over to an atomic64_t Jeff Layton
2016-12-22  8:38   ` Amir Goldstein
2016-12-22 13:27     ` Jeff Layton
2017-03-04  0:00   ` NeilBrown
2016-12-22  8:45 ` [RFC PATCH v1 00/30] fs: inode->i_version rework and optimization Christoph Hellwig
2016-12-22 14:42   ` Jeff Layton
2017-03-20 21:43     ` J. Bruce Fields
2017-03-21 13:45       ` Christoph Hellwig
2017-03-21 16:30         ` J. Bruce Fields [this message]
2017-03-21 17:23           ` Jeff Layton
2017-03-21 17:37             ` J. Bruce Fields
2017-03-21 17:51               ` J. Bruce Fields
2017-03-21 18:30             ` J. Bruce Fields
2017-03-21 18:46               ` Jeff Layton
2017-03-21 19:13                 ` J. Bruce Fields
2017-03-21 21:54                   ` Jeff Layton
2017-03-29 11:15                 ` Jan Kara
2017-03-29 17:54                   ` Jeff Layton
2017-03-29 23:41                     ` Dave Chinner
2017-03-30 11:24                       ` Jeff Layton
2017-04-04 18:38                       ` J. Bruce Fields
2017-03-30  6:47                     ` Jan Kara
2017-03-30 11:11                       ` Jeff Layton
2017-03-30 16:12                         ` J. Bruce Fields
2017-03-30 18:35                           ` Jeff Layton
2017-03-30 21:11                             ` Boaz Harrosh
2017-04-04 18:31                             ` J. Bruce Fields
2017-04-05  1:43                               ` NeilBrown
2017-04-05  8:05                                 ` Jan Kara
2017-04-05 18:14                                   ` J. Bruce Fields
2017-05-11 18:59                                     ` J. Bruce Fields
2017-05-11 22:22                                       ` NeilBrown
2017-05-12 16:21                                         ` J. Bruce Fields
2017-10-30 13:21                                           ` Jeff Layton
2017-05-12  8:27                                       ` Jan Kara
2017-05-12 15:56                                         ` J. Bruce Fields
2017-05-12 11:01                                       ` Jeff Layton
2017-05-12 15:57                                         ` J. Bruce Fields
2017-04-06  1:12                                   ` NeilBrown
2017-04-06  7:22                                     ` Jan Kara
2017-04-05 17:26                                 ` J. Bruce Fields
2017-04-01 23:05                           ` Dave Chinner
2017-04-03 14:00                             ` Jan Kara
2017-04-04 12:34                               ` Dave Chinner
2017-04-04 17:53                                 ` J. Bruce Fields
2017-04-05  1:26                                 ` NeilBrown
2017-03-21 21:45             ` Dave Chinner
2017-03-22 19:53               ` Jeff Layton
2017-03-03 23:00 ` J. Bruce Fields
2017-03-04  0:53   ` Jeff Layton
2017-03-08 17:29     ` J. Bruce Fields

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