linux-kernel - Re: [patch 2/3] slub: scan partial list for free slabs when thrashing

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Message-ID: <alpine.DEB.2.00.0903301317120.21074@chino.kir.corp.google.com>
Date:	Mon, 30 Mar 2009 13:22:55 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Christoph Lameter <cl@...ux.com>
cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Nick Piggin <nickpiggin@...oo.com.au>,
	Martin Bligh <mbligh@...gle.com>, linux-kernel@...r.kernel.org
Subject: Re: [patch 2/3] slub: scan partial list for free slabs when
 thrashing

On Mon, 30 Mar 2009, Christoph Lameter wrote:

> > Whenever a cpu cache satisfies a fastpath allocation, a fastpath counter
> > is incrememted.  This counter is cleared whenever the slowpath is
> > invoked.  This tracks how many fastpath allocations the cpu slab has
> > fulfilled before it must be refilled.
> 
> That adds fastpath overhead and it shows for small objects in your tests.
> 

Indeed, which is unavoidable in this case.  The only other way of tracking 
the "thrashing history" I can think of would be bitshifting a 1 for 
slowpath and 0 for fastpath, for example, into an unsigned long.  That, 
however, requires a hamming weight calculation in the slowpath and doesn't 
scale nearly as well as simply an incrementing a counter.

If there's other approaches on tracking such instances, I'd be interested 
to hear them.

Btw, is cl@...ux.com your new email address or are all 
linux-foundation.org emails going to eventually migrate to the new domain?
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