linux-kernel - Re: [PATCH 12/17] fs: Introduce per-bucket inode hash locks

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Message-ID: <20100930024331.GW5665@dastard>
Date:	Thu, 30 Sep 2010 12:43:31 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/17] fs: Introduce per-bucket inode hash locks

On Wed, Sep 29, 2010 at 09:52:14PM -0400, Christoph Hellwig wrote:
> 
> Instead of doing the lock overkill on a still fundamentally global data
> structure what about replacing this with something better.  I know
> you've already done this with the XFS icache, and while the per-AG
> concept obviously can't be generic at least some of the lessons could be
> applied.

The XFS inode cache design is tied tightly to the inode layout in
XFS, so the tree-per-ag-per-mount parallelism design really does not
work in a generic manner.  Sure, we could probably make it a
hashed-tree rather than hashed-link-list design, but that's a much
more fundamental change than just splitting the locks up.

> then again how much testing did this get anyway given that you
> benchmark ran mostly XFS which doesn't hit this at all?

I've been running comparitive benchmarks on ext4 as well so that I
also test all the generic paths.

> If it was up to me I'd dtop this (and the bl_list addition) from the
> series for now and wait for people who care about the scalability of
> the generic icache code to come up with a better data structure.

I think that it's going to take a lot of work to come up with
something more generically optimal, so in the mean time I think this
is a net win for filesystems that use the generic icache.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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