linux-kernel - Re: [RFC 00/15] x86_64: Optimize percpu accesses

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Date:	Thu, 10 Jul 2008 15:32:20 -0400
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Mike Travis <travis@....com>
CC:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jack Steiner <steiner@....com>, linux-kernel@...r.kernel.org,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [RFC 00/15] x86_64: Optimize percpu accesses

Mike Travis wrote:
> 
> The biggest growth came from moving all the xxx[NR_CPUS] arrays into
> the per cpu area.  So you free up a huge amount of unused memory when
> the NR_CPUS count starts getting into the ozone layer.  4k now, 16k
> real soon now, ??? future?
> 

Even (or perhaps especially) so, allocating the percpu area in 2 MB 
increments is a total nonstarter.  It hurts the small, common 
configurations way too much.  For SGI, it's probably fine.

	-hpa
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