From: Mark Tinguely <tinguely@sgi.com>
To: Dave Chinner <david@fromorbit.com>
Cc: xfs@oss.sgi.com
Subject: Re: [PATCH] [RFC] xfs: lookaside cache for xfs_buf_find
Date: Thu, 19 Sep 2013 08:23:32 -0500 [thread overview]
Message-ID: <523AFAD4.4040208@sgi.com> (raw)
In-Reply-To: <20130918232409.GF9901@dastard>
On 09/18/13 18:24, Dave Chinner wrote:
> On Wed, Sep 18, 2013 at 04:48:45PM -0500, Mark Tinguely wrote:
>> On 09/08/13 20:33, Dave Chinner wrote:
>>> From: Dave Chinner<dchinner@redhat.com>
>>>
>>> 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.
> ....
>>
>> Low cost, possible higher return. Idea looks good to me.
>>
>> What happens in xfs_buf_get_map() when we lose the xfs_buf_find() race?
>
> What race is that?
I am thinking the two overlapping callers to xfs_buf_find() protected by
the two calls to xfs_buf_find(). But my mistake was where the lookaside
gets added. It is added correctly on the second call to xfs_buf_find()
where it make sure that another find did not beat this find. Yes, no
entry needs to be removed.
--Mark.
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next prev parent reply other threads:[~2013-09-19 13:23 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-09-09 1:33 [PATCH] [RFC] xfs: lookaside cache for xfs_buf_find Dave Chinner
2013-09-09 15:17 ` Mark Tinguely
2013-09-09 15:39 ` Dave Chinner
2013-09-18 21:48 ` Mark Tinguely
2013-09-18 23:24 ` Dave Chinner
2013-09-19 13:23 ` Mark Tinguely [this message]
2013-09-23 14:17 ` Mark Tinguely
2013-09-23 21:25 ` Michael L. Semon
2013-09-24 0:48 ` Dave Chinner
2013-09-24 17:41 ` Mark Tinguely
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