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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: Mon, 09 Sep 2013 10:17:24 -0500
Cc: xfs@xxxxxxxxxxx
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <1378690396-15792-1-git-send-email-david@xxxxxxxxxxxxx>
References: <1378690396-15792-1-git-send-email-david@xxxxxxxxxxxxx>
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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.

Add a hashed lookaside buffer that records the recent buffer
lookup successes and is searched first before doing a rb-tree
lookup. If we get a hit, we avoid the expensive rbtree lookup and
greatly reduce the overhead of the lookup. If we get a cache miss,
then we've added an extra CPU cacheline miss into the lookup.

Interesting. The last allocated xfs_buf is placed into the hash.

Might be interesting to know the hit-miss ratio on a real workload.

--Mark.

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