linux-kernel - Re: [man-pages RFC PATCH v4] statx, inode: document the new STATX_INO

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Date:   Fri, 09 Sep 2022 10:43:30 -0400
From:   Jeff Layton <jlayton@...nel.org>
To:     Theodore Ts'o <tytso@....edu>
Cc:     "J. Bruce Fields" <bfields@...ldses.org>, Jan Kara <jack@...e.cz>,
        NeilBrown <neilb@...e.de>, adilger.kernel@...ger.ca,
        djwong@...nel.org, david@...morbit.com, trondmy@...merspace.com,
        viro@...iv.linux.org.uk, zohar@...ux.ibm.com, xiubli@...hat.com,
        chuck.lever@...cle.com, lczerner@...hat.com, brauner@...nel.org,
        fweimer@...hat.com, linux-man@...r.kernel.org,
        linux-api@...r.kernel.org, linux-btrfs@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
        ceph-devel@...r.kernel.org, linux-ext4@...r.kernel.org,
        linux-nfs@...r.kernel.org, linux-xfs@...r.kernel.org
Subject: Re: [man-pages RFC PATCH v4] statx, inode: document the new
 STATX_INO_VERSION field

On Fri, 2022-09-09 at 09:48 -0400, Theodore Ts'o wrote:
> On Fri, Sep 09, 2022 at 08:47:17AM -0400, Jeff Layton wrote:
> > 
> > i_version only changes now if someone has queried it since it was last
> > changed. That makes a huge difference in performance. We can try to
> > optimize it further, but it probably wouldn't move the needle much under
> > real workloads.
> 
> Good point.  And to be clear, from NFS's perspective, you only need to
> have i_version bumped if there is a user-visible change to the
> file. --- with an explicit exception here of the FIEMAP system call,
> since in the case of a delayed allocation, FIEMAP might change from
> reporting:
> 
>  ext:     logical_offset:        physical_offset: length:   expected: flags:
>    0:        0..       0:          0..         0:      0:             last,unknown_loc,delalloc,eof
> 
> to this:
> 
>  ext:     logical_offset:        physical_offset: length:   expected: flags:
>    0:        0..       0:  190087172.. 190087172:      1:             last,eof
> 
> after a sync(2) or fsync(2) call, or after time passes.
> 

In general, we want to bump i_version if the ctime changes. I'm guessing
that we don't change ctime on a delalloc? If it's not visible to NFS,
then NFS won't care about it.  We can't project FIEMAP info across the
wire at this time, so we'd probably like to avoid seeing an i_version
bump in due to delalloc.

> > Great! That's what I was hoping for with ext4. Would you be willing to
> > pick up these two patches for v6.1?
> > 
> > https://lore.kernel.org/linux-ext4/20220908172448.208585-3-jlayton@kernel.org/T/#u
> > https://lore.kernel.org/linux-ext4/20220908172448.208585-4-jlayton@kernel.org/T/#u
> 
> I think you mean:
> 
> https://lore.kernel.org/linux-ext4/20220908172448.208585-2-jlayton@kernel.org/T/#u
> https://lore.kernel.org/linux-ext4/20220908172448.208585-3-jlayton@kernel.org/T/#u
> 
> Right?
> 
> BTW, sorry for not responding to these patches earlier; between
> preparing for the various Linux conferences in Dublin next week, and
> being in Zurich and meeting with colleagues at $WORK all of this week,
> I'm a bit behind on my patch reviews.
> 

No worries. As long as they're on your radar, that's fine.

Thanks!
-- 
Jeff Layton <jlayton@...nel.org>