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[68.20.15.154]) by smtp.gmail.com with ESMTPSA id s15sm6751128qtc.95.2020.06.19.05.04.53 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 19 Jun 2020 05:04:53 -0700 (PDT) Message-ID: Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts From: Jeff Layton To: Dave Chinner , "J. Bruce Fields" Cc: Masayoshi Mizuma , Eric Sandeen , "Darrick J. Wong" , Christoph Hellwig , Theodore Ts'o , Andreas Dilger , Alexander Viro , Masayoshi Mizuma , linux-ext4@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-xfs Date: Fri, 19 Jun 2020 08:04:53 -0400 In-Reply-To: <20200619024455.GN2005@dread.disaster.area> References: <20200617172456.GP11245@magnolia> <8f0df756-4f71-9d96-7a52-45bf51482556@sandeen.net> <20200617181816.GA18315@fieldses.org> <4cbb5cbe-feb4-2166-0634-29041a41a8dc@sandeen.net> <20200617184507.GB18315@fieldses.org> <20200618013026.ewnhvf64nb62k2yx@gabell> <20200618030539.GH2005@dread.disaster.area> <20200618034535.h5ho7pd4eilpbj3f@gabell> <20200618223948.GI2005@dread.disaster.area> <20200619022005.GA25414@fieldses.org> <20200619024455.GN2005@dread.disaster.area> Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.36.3 (3.36.3-1.fc32) MIME-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org On Fri, 2020-06-19 at 12:44 +1000, Dave Chinner wrote: > On Thu, Jun 18, 2020 at 10:20:05PM -0400, J. Bruce Fields wrote: > > On Fri, Jun 19, 2020 at 08:39:48AM +1000, Dave Chinner wrote: > > > On Wed, Jun 17, 2020 at 11:45:35PM -0400, Masayoshi Mizuma wrote: > > > > Thank you for pointed it out. > > > > How about following change? I believe it works both xfs and btrfs... > > > > > > > > diff --git a/fs/super.c b/fs/super.c > > > > index b0a511bef4a0..42fc6334d384 100644 > > > > --- a/fs/super.c > > > > +++ b/fs/super.c > > > > @@ -973,6 +973,9 @@ int reconfigure_super(struct fs_context *fc) > > > > } > > > > } > > > > > > > > + if (sb->s_flags & SB_I_VERSION) > > > > + fc->sb_flags |= MS_I_VERSION; > > > > + > > > > WRITE_ONCE(sb->s_flags, ((sb->s_flags & ~fc->sb_flags_mask) | > > > > (fc->sb_flags & fc->sb_flags_mask))); > > > > /* Needs to be ordered wrt mnt_is_readonly() */ > > > > > > This will prevent SB_I_VERSION from being turned off at all. That > > > will break existing filesystems that allow SB_I_VERSION to be turned > > > off on remount, such as ext4. > > > > > > The manipulations here need to be in the filesystem specific code; > > > we screwed this one up so badly there is no "one size fits all" > > > behaviour that we can implement in the generic code... > > > > 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. > > > But looking back through Jeff's postings, I don't see him claiming that; > > e.g. in: > > > > https://lore.kernel.org/lkml/20171222120556.7435-1-jlayton@kernel.org/ > > https://lore.kernel.org/linux-nfs/20180109141059.25929-1-jlayton@kernel.org/ > > https://lore.kernel.org/linux-nfs/1517228795.5965.24.camel@redhat.com/ > > > > he reports comparing old iversion behavior to new iversion behavior, but > > not new iversion behavior to new noiversion behavior. > > Yeah, it's had to compare noiversion behaviour on filesystems where > it was understood that it couldn't actually be turned off. And, > realistically, the comaprison to noiversion wasn't really relevant > to the problem Jeff's patchset was addressing... > I actually did do some comparison with that patchset vs. noiversion mounted ext4, and found that there was a small performance delta. It wasn't much but it was measurable enough that I didn't want to propose removing the option from ext4 altogether at the time. It may be worth it to do that now though. -- Jeff Layton