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

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Message-Id: <1238483617.26587.32.camel@penberg-laptop>
Date:	Tue, 31 Mar 2009 10:13:37 +0300
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Christoph Lameter <cl@...ux.com>
Cc:	David Rientjes <rientjes@...gle.com>,
	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 Sun, 29 Mar 2009, David Rientjes 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.

On Mon, 2009-03-30 at 10:37 -0400, Christoph Lameter wrote:
> That adds fastpath overhead and it shows for small objects in your tests.

Yup, and looking at this:

+       u16 fastpath_allocs;    /* Consecutive fast allocs before slowpath */
+       u16 slowpath_allocs;    /* Consecutive slow allocs before watermark */

How much do operations on u16 hurt on, say, x86-64? It's nice that
sizeof(struct kmem_cache_cpu) is capped at 32 bytes but on CPUs that
have bigger cache lines, the types could be wider.

Christoph, why is struct kmem_cache_cpu not __cacheline_aligned_in_smp
btw?

			Pekka

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