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Date:   Sat, 20 Jun 2020 13:09:24 -0400
From:   "J. Bruce Fields" <bfields@fieldses.org>
To:     Eric Sandeen <sandeen@sandeen.net>
Cc:     Dave Chinner <david@fromorbit.com>,
        Masayoshi Mizuma <msys.mizuma@gmail.com>,
        "Darrick J. Wong" <darrick.wong@oracle.com>,
        Christoph Hellwig <hch@infradead.org>,
        Theodore Ts'o <tytso@mit.edu>,
        Andreas Dilger <adilger.kernel@dilger.ca>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Masayoshi Mizuma <m.mizuma@jp.fujitsu.com>,
        linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org,
        linux-xfs <linux-xfs@vger.kernel.org>, jlayton@redhat.com
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts
Message-ID: <20200620170924.GI1514@fieldses.org>
References: <20200618034535.h5ho7pd4eilpbj3f@gabell>
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On Sat, Jun 20, 2020 at 12:00:43PM -0500, Eric Sandeen wrote:
> On 6/19/20 8:56 PM, J. Bruce Fields wrote:
> > On Sat, Jun 20, 2020 at 11:49:57AM +1000, Dave Chinner wrote:
> 
> ...
> 
> >> However, other people have different opinions on this matter (and we
> >> know that from the people who considered XFS v4 -> v5 going slower
> >> because iversion a major regression), and so we must acknowledge
> >> those opinions even if we don't agree with them.
> > 
> > Do you have any of those reports handy?  Were there numbers?
> 
> I can't answer that but did a little digging.  MS_I_VERSION as an option
> appeared here:
> 
...
> so the optional enablement was there on day one, without any real explanation
> of why.

My memory is that they didn't have measurements at first, but worried
that there might be a performance issue.  Which later mesurements
confirmed.

But that Jeff Layton's work eliminated most of that.

I think ext4 was the focuse of the concern, but xfs might also have had
a (less serious) regression, and btrfs might have actually had it worst?

But I don't have references and my memory may be wrong.

--b.