Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts

From: "J. Bruce Fields" <bfields@fieldses.org>
To: Dave Chinner <david@fromorbit.com>
Cc: Masayoshi Mizuma <msys.mizuma@gmail.com>,
	Eric Sandeen <sandeen@sandeen.net>,
	"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
Date: Fri, 19 Jun 2020 21:56:33 -0400	[thread overview]
Message-ID: <20200620015633.GA1516@fieldses.org> (raw)
In-Reply-To: <20200620014957.GQ2005@dread.disaster.area>

On Sat, Jun 20, 2020 at 11:49:57AM +1000, Dave Chinner wrote:
> On Fri, Jun 19, 2020 at 06:28:43PM -0400, J. Bruce Fields wrote:
> > On Sat, Jun 20, 2020 at 08:10:44AM +1000, Dave Chinner wrote:
> > > On Fri, Jun 19, 2020 at 04:40:33PM -0400, J. Bruce Fields wrote:
> > > > On Fri, Jun 19, 2020 at 12:44:55PM +1000, Dave Chinner wrote:
> > > > > On Thu, Jun 18, 2020 at 10:20:05PM -0400, J. Bruce Fields wrote:
> > > > > > My memory was that after Jeff Layton's i_version patches, there wasn't
> > > > > > really a significant performance hit any more, so the ability to turn it
> > > > > > off is no longer useful.
> > > > > 
> > > > > Yes, I completely agree with you here. However, with some
> > > > > filesystems allowing it to be turned off, we can't just wave our
> > > > > hands and force enable the option. Those filesystems - if the
> > > > > maintainers chose to always enable iversion - will have to go
> > > > > through a mount option deprecation period before permanently
> > > > > enabling it.
> > > > 
> > > > I don't understand why.
> > > > 
> > > > The filesystem can continue to let people set iversion or noiversion as
> > > > they like, while under the covers behaving as if iversion is always set.
> > > > I can't see how that would break any application.  (Or even how an
> > > > application would be able to detect that the filesystem was doing this.)
> > > 
> > > It doesn't break functionality, but it affects performance.
> > 
> > I thought you just agreed above that any performance hit was not
> > "significant".
> 
> Yes, but that's just /my opinion/.
> 
> 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?

--b.