linux-kernel - Re: [PATCHSET] percpu: generalize first chunk allocators and improve lpage NUMA support

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Date:	Wed, 1 Jul 2009 00:31:38 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Christoph Lameter <cl@...ux-foundation.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, tj@...nel.org,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-arch@...r.kernel.org, andi@...stfloor.org, hpa@...or.com,
	tglx@...utronix.de
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and
	improve lpage NUMA support


* Christoph Lameter <cl@...ux-foundation.org> wrote:

> On Tue, 30 Jun 2009, Ingo Molnar wrote:
> 
> > But what if not? What if the kernel can run on up to 4096 CPUs 
> > and runs on a big box. Why should a virtual machine have the 
> > illogical choice between either wasting a lot of RAM 
> > preallocating stuff, or limiting its own extendability.
> 
> The kernel may be able to run on 4096 but the machines config 
> information that is available via ACPI knows how many processors 
> the machine we are booting on is able to add.

I think we might be talking past each other.

The usecase i'm talking about is to boot a generic, 
many-CPUs-capable kernel in a guest image.

How would you allow that guest to stay on 2 virtual CPUs but still 
be able to hot-plug many other CPUs if the guest context rises above 
its original CPU utilization?

	Ingo
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