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Re: working on extent locks for i_mutex

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: working on extent locks for i_mutex
From: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
Date: Fri, 13 Jan 2012 13:50:52 -0700
Cc: Lukas Czerner <lczerner@xxxxxxxxxx>, Ext4 Developers List <linux-ext4@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
In-reply-to: <20120113043411.GH2806@dastard>
References: <4F0F9E97.1090403@xxxxxxxxxxxxxxxxxx> <20120113043411.GH2806@dastard>
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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.

Cheers,

Dave.

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!

Allison Henderson

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