From: David Sterba <dsterba@suse.cz>
To: Dave Chinner <david@fromorbit.com>
Cc: Liu Bo <bo.li.liu@oracle.com>,
linux-btrfs@vger.kernel.org, fdmanana@suse.com, kzak@redhat.com,
linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: i_version vs iversion (Was: Re: [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION)
Date: Wed, 24 Jun 2015 19:28:04 +0200 [thread overview]
Message-ID: <20150624172804.GB726@suse.cz> (raw)
In-Reply-To: <20150622204215.GA1557@dastard>
On Tue, Jun 23, 2015 at 06:42:15AM +1000, Dave Chinner wrote:
> On Thu, Jun 18, 2015 at 04:38:56PM +0200, David Sterba wrote:
> > Moving the discussion to fsdevel.
> >
> > Summary: disabling MS_I_VERSION brings some speedups to btrfs, but the
> > generic 'noiversion' option cannot be used to achieve that. It is
> > processed before it reaches btrfs superblock callback, where
> > MS_I_VERSION is forced.
> >
> > The proposed fix is to add btrfs-specific i_version/noi_version to btrfs,
> > to which I object.
>
> The issue is that you can't overide IS_I_VERSION(inode) because it
> looks at the superblock flag, yes?
Effectively, yes.
> So perhaps IS_I_VERSION should become an inode flag, set by the
> filesystem at inode instantiation time, and hence filesystems can
> choose on a per-inode basis if they want I_VERSION behaviour or not.
Sounds good, I like that. Looking at the proposed usecase again, the
performance speedup needs the NODATACOW bit set as well, so setting
one more bit is not a big deal.
Besides, the global 'noi_version' does not have the expected effect
because inode::i_version is incremented unconditionally everywhere
(except 1 call site). From that perspective I think that the
inode-specific bit is the right approach.
> At that point, the behaviour of MS_I_VERSION becomes irrelevant to
> the discussion, doesn't it?
Agreed.
> > xfs also forces I_VERSION if it detects the superblock version 5, so it
> > could use the same fix that would work for btrfs.
>
> XFS is a special snowflake - it updates the I_VERSION only when an
> inode is otherwise modified in a transaction, so turning it off
> saves nothing. (And yes, timestamp updates are transactional in
> XFS). Hence XFS behaviour is irrelevant to the discussion, because
> we aren't ever going to turn it off....
Understood.
Thanks for the feedback.
next prev parent reply other threads:[~2015-06-24 17:28 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-06-17 7:54 [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION Liu Bo
2015-06-17 7:54 ` [RFC PATCH v2 2/2] Btrfs: improve fsync for nocow file Liu Bo
2015-06-17 15:58 ` David Sterba
2015-06-18 3:27 ` Liu Bo
2015-06-24 18:21 ` David Sterba
2015-06-25 2:24 ` Liu Bo
2015-06-25 16:10 ` David Sterba
2015-06-17 15:33 ` [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION David Sterba
2015-06-17 15:52 ` Liu Bo
2015-06-17 17:01 ` David Sterba
2015-06-18 2:46 ` Liu Bo
2015-06-18 14:38 ` i_version vs iversion (Was: Re: [RFC PATCH v2 1/2] Btrfs: add noi_version option to disable MS_I_VERSION) David Sterba
2015-06-19 11:44 ` Karel Zak
2015-06-19 11:44 ` Karel Zak
2015-06-22 20:42 ` Dave Chinner
2015-06-22 20:42 ` Dave Chinner
2015-06-24 17:28 ` David Sterba [this message]
2015-06-23 16:32 ` Theodore Ts'o
2015-06-24 8:23 ` Liu Bo
2015-06-24 18:02 ` David Sterba
2015-06-24 23:17 ` Theodore Ts'o
2015-06-24 23:17 ` Theodore Ts'o
2015-06-24 23:59 ` Dave Chinner
2015-06-24 23:59 ` Dave Chinner
2015-06-25 18:46 ` J. Bruce Fields
2015-06-25 18:46 ` J. Bruce Fields
2015-06-25 22:12 ` Theodore Ts'o
2015-06-26 13:32 ` J. Bruce Fields
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