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Re: [PATCH] [RFC] xfs: lookaside cache for xfs_buf_find

To: Dave Chinner <david@xxxxxxxxxxxxx>
Subject: Re: [PATCH] [RFC] xfs: lookaside cache for xfs_buf_find
From: Mark Tinguely <tinguely@xxxxxxx>
Date: Tue, 24 Sep 2013 12:41:54 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130924004803.GZ9901@dastard>
References: <1378690396-15792-1-git-send-email-david@xxxxxxxxxxxxx> <52404D7F.1080308@xxxxxxx> <20130924004803.GZ9901@dastard>
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On 09/23/13 19:48, Dave Chinner wrote:
On Mon, Sep 23, 2013 at 09:17:35AM -0500, Mark Tinguely wrote:
On 09/08/13 20:33, Dave Chinner wrote:
From: Dave Chinner<dchinner@xxxxxxxxxx>

CPU overhead of buffer lookups dominate most metadata intensive
workloads. The thing is, most such workloads are hitting a
relatively small number of buffers repeatedly, and so caching
recently hit buffers is a good idea.

...

I think this needs more testing.

Yes, that's what an "RFC" implies. It's an idea, it's not
fully baked and it's not ready for inclusion - it's a proof of
concept that needs further work, and I't being posted for discussion
to determine if it's worth pursuing further.

Indeed, I haven't proposed it for inclusion yet because I'm
still finding problems caused by the patch - it's still just a
prototype at this point.

I got the same panic running xfstest 319 with the patch at:
    http://oss.sgi.com/archives/xfs/2013-09/msg00578.html
once it hung on a xfs_buf lock before the panic.

And these are the only tests that I threw at this patch.

Sure. The version I have in my stack at the moment has some more
ixes in it, like handling of length mismatches due to stale buffers
on lookaside lookups, and other such things.

i.e. early feedback on prototype code is exactly what [RFC] patches
are for...

And early feedback is that it has potential but needs more work.

--Mark.

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