linux-kernel - Re: [PATCH] mm-slab: allocate kmem_cache with __GFP

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Message-ID: <alpine.DEB.2.00.1107201114480.1472@router.home>
Date:	Wed, 20 Jul 2011 11:17:57 -0500 (CDT)
From:	Christoph Lameter <cl@...ux.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
cc:	Mel Gorman <mgorman@...e.de>, Pekka Enberg <penberg@...nel.org>,
	Konstantin Khlebnikov <khlebnikov@...nvz.org>,
	Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Matt Mackall <mpm@...enic.com>
Subject: Re: [PATCH] mm-slab: allocate kmem_cache with __GFP_REPEAT

On Wed, 20 Jul 2011, Eric Dumazet wrote:

> Note that adding ____cacheline_aligned_in_smp on nodelists[] actually
> helps performance, as all following fields are readonly after kmem_cache
> setup.

Well but that is not addresssing the same issue. Could you separate that
out?

The other question that follows from this is then: Does that
alignment compensate for the loss of performance due to the additional
lookup in hot code paths and the additional cacheline reference required?

The per node pointers are lower priority in terms of performance than the
per cpu pointers. I'd rather have the per node pointers requiring an
additional lookup. Less impact on hot code paths.

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