linux-kernel - Re: [patch 3/4] cpu alloc: The allocator

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Message-Id: <200810060810.43511.rusty@rustcorp.com.au>
Date:	Mon, 6 Oct 2008 07:10:43 +1000
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org, jeremy@...p.org,
	ebiederm@...ssion.com, travis@....com, herbert@...dor.apana.org.au,
	xemul@...nvz.org, penberg@...helsinki.fi
Subject: Re: [patch 3/4] cpu alloc: The allocator

On Friday 03 October 2008 22:48:32 Christoph Lameter wrote:
> Andrew Morton wrote:
> > But I'd have though that it would be possible to only allocate the
> > storage for online CPUs.  That would be a pretty significant win for
> > some system configurations?
>
> We  have tried that but currently the kernel (core and in particular arch
> code) keeps state for all possible cpus in percpu segments. Would require
> more extensive cleanup of numerous arches to do.

It shouldn't be a big win, since possible ~= online for most systems.  And 
having all the per-cpu users register online and offline cpu callbacks is 
error prone and a PITA.

Rusty.
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