Received-SPF: pass (google.com: domain of linux-ext4-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH] fs: i_version mntopt gets visible through /proc/mounts
To:     "J. Bruce Fields" <bfields@fieldses.org>,
        Dave Chinner <david@fromorbit.com>
Cc:     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
References: <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>
 <20200619204033.GB1564@fieldses.org>
 <20200619221044.GO2005@dread.disaster.area>
 <20200619222843.GB2650@fieldses.org>
 <20200620014957.GQ2005@dread.disaster.area>
 <20200620015633.GA1516@fieldses.org>
From:   Eric Sandeen <sandeen@sandeen.net>
Autocrypt: addr=sandeen@sandeen.net; prefer-encrypt=mutual; keydata=
 mQINBE6x99QBEADMR+yNFBc1Y5avoUhzI/sdR9ANwznsNpiCtZlaO4pIWvqQJCjBzp96cpCs
 nQZV32nqJBYnDpBDITBqTa/EF+IrHx8gKq8TaSBLHUq2ju2gJJLfBoL7V3807PQcI18YzkF+
 WL05ODFQ2cemDhx5uLghHEeOxuGj+1AI+kh/FCzMedHc6k87Yu2ZuaWF+Gh1W2ix6hikRJmQ
 vj5BEeAx7xKkyBhzdbNIbbjV/iGi9b26B/dNcyd5w2My2gxMtxaiP7q5b6GM2rsQklHP8FtW
 ZiYO7jsg/qIppR1C6Zr5jK1GQlMUIclYFeBbKggJ9mSwXJH7MIftilGQ8KDvNuV5AbkronGC
 sEEHj2khs7GfVv4pmUUHf1MRIvV0x3WJkpmhuZaYg8AdJlyGKgp+TQ7B+wCjNTdVqMI1vDk2
 BS6Rg851ay7AypbCPx2w4d8jIkQEgNjACHVDU89PNKAjScK1aTnW+HNUqg9BliCvuX5g4z2j
 gJBs57loTWAGe2Ve3cMy3VoQ40Wt3yKK0Eno8jfgzgb48wyycINZgnseMRhxc2c8hd51tftK
 LKhPj4c7uqjnBjrgOVaVBupGUmvLiePlnW56zJZ51BR5igWnILeOJ1ZIcf7KsaHyE6B1mG+X
 dmYtjDhjf3NAcoBWJuj8euxMB6TcQN2MrSXy5wSKaw40evooGwARAQABtCVFcmljIFIuIFNh
 bmRlZW4gPHNhbmRlZW5Ac2FuZGVlbi5uZXQ+iQI7BBMBAgAlAhsDBgsJCAcDAgYVCAIJCgsE
 FgIDAQIeAQIXgAUCUzMzbAIZAQAKCRAgrhaS4T3e4Fr7D/wO+fenqVvHjq21SCjDCrt8HdVj
 aJ28B1SqSU2toxyg5I160GllAxEHpLFGdbFAhQfBtnmlY9eMjwmJb0sCIrkrB6XNPSPA/B2B
 UPISh0z2odJv35/euJF71qIFgWzp2czJHkHWwVZaZpMWWNvsLIroXoR+uA9c2V1hQFVAJZyk
 EE4xzfm1+oVtjIC12B9tTCuS00pY3AUy21yzNowT6SSk7HAzmtG/PJ/uSB5wEkwldB6jVs2A
 sjOg1wMwVvh/JHilsQg4HSmDfObmZj1d0RWlMWcUE7csRnCE0ZWBMp/ttTn+oosioGa09HAS
 9jAnauznmYg43oQ5Akd8iQRxz5I58F/+JsdKvWiyrPDfYZtFS+UIgWD7x+mHBZ53Qjazszox
 gjwO9ehZpwUQxBm4I0lPDAKw3HJA+GwwiubTSlq5PS3P7QoCjaV8llH1bNFZMz2o8wPANiDx
 5FHgpRVgwLHakoCU1Gc+LXHXBzDXt7Cj02WYHdFzMm2hXaslRdhNGowLo1SXZFXa41KGTlNe
 4di53y9CK5ynV0z+YUa+5LR6RdHrHtgywdKnjeWdqhoVpsWIeORtwWGX8evNOiKJ7j0RsHha
 WrePTubr5nuYTDsQqgc2r4aBIOpeSRR2brlT/UE3wGgy9LY78L4EwPR0MzzecfE1Ws60iSqw
 Pu3vhb7h3bkCDQROsffUARAA0DrUifTrXQzqxO8aiQOC5p9Tz25Np/Tfpv1rofOwL8VPBMvJ
 X4P5l1V2yd70MZRUVgjmCydEyxLJ6G2YyHO2IZTEajUY0Up+b3ErOpLpZwhvgWatjifpj6bB
 SKuDXeThqFdkphF5kAmgfVAIkan5SxWK3+S0V2F/oxstIViBhMhDwI6XsRlnVBoLLYcEilxA
 2FlRUS7MOZGmRJkRtdGD5koVZSM6xVZQSmfEBaYQ/WJBGJQdPy94nnlAVn3lH3+N7pXvNUuC
 GV+t4YUt3tLcRuIpYBCOWlc7bpgeCps5Xa0dIZgJ8Louu6OBJ5vVXjPxTlkFdT0S0/uerCG5
 1u8p6sGRLnUeAUGkQfIUqGUjW2rHaXgWNvzOV6i3tf9YaiXKl3avFaNW1kKBs0T5M1cnlWZU
 Utl6k04lz5OjoNY9J/bGyV3DSlkblXRMK87iLYQSrcV6cFz9PRl4vW1LGff3xRQHngeN5fPx
 ze8X5NE3hb+SSwyMSEqJxhVTXJVfQWWW0dQxP7HNwqmOWYF/6m+1gK/Y2gY3jAQnsWTru4RV
 TZGnKwEPmOCpSUvsTRXsVHgsWJ70qd0yOSjWuiv4b8vmD3+QFgyvCBxPMdP3xsxN5etheLMO
 gRwWpLn6yNFq/xtgs+ECgG+gR78yXQyA7iCs5tFs2OrMqV5juSMGmn0kxJUAEQEAAYkCHwQY
 AQIACQUCTrH31AIbDAAKCRAgrhaS4T3e4BKwD/0ZOOmUNOZCSOLAMjZx3mtYtjYgfUNKi0ki
 YPveGoRWTqbis8UitPtNrG4XxgzLOijSdOEzQwkdOIp/QnZhGNssMejCnsluK0GQd+RkFVWN
 mcQT78hBeGcnEMAXZKq7bkIKzvc06GFmkMbX/gAl6DiNGv0UNAX+5FYh+ucCJZSyAp3sA+9/
 LKjxnTedX0aygXA6rkpX0Y0FvN/9dfm47+LGq7WAqBOyYTU3E6/+Z72bZoG/cG7ANLxcPool
 LOrU43oqFnD8QwcN56y4VfFj3/jDF2MX3xu4v2OjglVjMEYHTCxP3mpxesGHuqOit/FR+mF0
 MP9JGfj6x+bj/9JMBtCW1bY/aPeMdPGTJvXjGtOVYblGZrSjXRn5++Uuy36CvkcrjuziSDG+
 JEexGxczWwN4mrOQWhMT5Jyb+18CO+CWxJfHaYXiLEW7dI1AynL4jjn4W0MSiXpWDUw+fsBO
 Pk6ah10C4+R1Jc7dyUsKksMfvvhRX1hTIXhth85H16706bneTayZBhlZ/hK18uqTX+s0onG/
 m1F3vYvdlE4p2ts1mmixMF7KajN9/E5RQtiSArvKTbfsB6Two4MthIuLuf+M0mI4gPl9SPlf
 fWCYVPhaU9o83y1KFbD/+lh1pjP7bEu/YudBvz7F2Myjh4/9GUAijrCTNeDTDAgvIJDjXuLX pA==
Message-ID: <d6f9cac3-eec0-a88e-4eab-7673728db52c@sandeen.net>
Date:   Sat, 20 Jun 2020 12:00:43 -0500
User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:68.0)
 Gecko/20100101 Thunderbird/68.9.0
MIME-Version: 1.0
In-Reply-To: <20200620015633.GA1516@fieldses.org>
Content-Type: text/plain; charset=utf-8
Content-Language: en-US
Content-Transfer-Encoding: 8bit
Sender: linux-ext4-owner@vger.kernel.org
Precedence: bulk

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:

commit 7a224228ed79d587ece2304869000aad1b8e97dd
Author: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
Date:   Mon Jan 28 23:58:27 2008 -0500

    vfs: Add 64 bit i_version support
    
    The i_version field of the inode is changed to be a 64-bit counter that
    is set on every inode creation and that is incremented every time the
    inode data is modified (similarly to the "ctime" time-stamp).
    The aim is to fulfill a NFSv4 requirement for rfc3530.
    This first part concerns the vfs, it converts the 32-bit i_version in
    the generic inode to a 64-bit, a flag is added in the super block in
    order to check if the feature is enabled and the i_version is
    incremented in the vfs.
    
    Signed-off-by: Mingming Cao <cmm@us.ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
    Signed-off-by: Kalpak Shah <kalpak@clusterfs.com>

and ext4's Opt_i_version mount option appeared here:

commit 25ec56b518257a56d2ff41a941d288e4b5ff9488
Author: Jean Noel Cordenner <jean-noel.cordenner@bull.net>
Date:   Mon Jan 28 23:58:27 2008 -0500

    ext4: Add inode version support in ext4
    
    This patch adds 64-bit inode version support to ext4. The lower 32 bits
    are stored in the osd1.linux1.l_i_version field while the high 32 bits
    are stored in the i_version_hi field newly created in the ext4_inode.
    This field is incremented in case the ext4_inode is large enough. A
    i_version mount option has been added to enable the feature.
    
    Signed-off-by: Mingming Cao <cmm@us.ibm.com>
    Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
    Signed-off-by: Kalpak Shah <kalpak@clusterfs.com>
    Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
    Signed-off-by: Jean Noel Cordenner <jean-noel.cordenner@bull.net>

so the optional enablement was there on day one, without any real explanation
of why.

-Eric