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

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Date:	Wed, 24 Jun 2009 17:13:37 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Andi Kleen <andi@...stfloor.org>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org, mingo@...e.hu,
	tglx@...utronix.de, cl@...ux-foundation.org
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and improve
 lpage NUMA support

Andi Kleen wrote:
> 
> Haven't read the new patches, but per cpu data always was sized
> for all possible CPUs.
> 
>> and N is large, what did it cost?
> 
>> And what are reasonable values of N?
> 
> N should normally not be large anymore, since num_possible_cpus() 
> is sized based on firmware information now.
> 

*Ahem* virtual machines *ahem*...

I have discussed this with Tejun, and the plan is to allocate the percpu
information when a processor is first brought online (but not removed
when it is offlined again.)  It's a real problem for 32-bit VMs, so it's
more important than you'd think.

	-hpa

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