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Date:	Mon, 16 Jan 2012 10:57:47 +1100
From:	Dave Chinner <>
To:	Allison Henderson <>
Cc:	Lukas Czerner <>,
	Ext4 Developers List <>,
Subject: Re: working on extent locks for i_mutex

On Fri, Jan 13, 2012 at 01:50:52PM -0700, Allison Henderson wrote:
> On 01/12/2012 09:34 PM, Dave Chinner wrote:
> >On Thu, Jan 12, 2012 at 08:01:43PM -0700, Allison Henderson wrote:
> >>Hi All,
> >>
> >>I know this is an old topic, but I am poking it again because I've
> >>had some work items wrap up, and Im planning on picking up on this
> >>one again.  I am thinking about implementing extent locks to replace
> >>i_mutex.  So I just wanted to touch base with folks and see what
> >>people are working on because I know there were some folks out there
> >>that were thing about doing similar solutions.
> >
> >What locking API are you looking at? If you are looking at an
> >something like:
> >
> >read_range_{try}lock(lock, off, len)
> >read_range_unlock(lock, off, len)
> >write_range_{try}lock(lock, off, len)
> >write_range_unlock(lock, off, len)
> >
> >and implementing with an rbtree or a btree for tracking, then I
> >definitely have a use for it in XFS - replacing the current rwsem
> >that is used for the iolock. Range locks like this are the only
> >thing we need to allow concurrent buffered writes to the same file
> >to maintain the per-write exclusion that posix requires.
> Yes that is generally the idea I was thinking about doing, but at
> the time, I was not thinking outside the scope of ext4.  You are
> thinking maybe it should be in vfs layer so that it's something that
> all the filesystems will use?  That seems to be the impression I'm
> getting from folks.  Thx!

Yes, that's what I'm suggesting. Not so much a vfs layer function,
but a library (range locks could be useful outside filesystems) so
locating it in lib/ was what I was thinking....


Dave Chinner
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