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

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Date:	Tue, 30 Jun 2009 16:34:05 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Ingo Molnar <mingo@...e.hu>
CC:	Tejun Heo <tj@...nel.org>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, x86@...nel.org,
	linux-arch@...r.kernel.org, andi@...stfloor.org, tglx@...utronix.de
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and	improve
 lpage NUMA support

Ingo Molnar wrote:
> * Tejun Heo <tj@...nel.org> wrote:
> 
>> Hello, Christoph.
>>
>> Christoph Lameter wrote:
> 
>>> I looked at allocating for online cpus only a couple of years 
>>> back but at that per cpu state was kept for offlined cpus in per 
>>> cpu areas. There are numerous assumptions in per cpu handling 
>>> all over the kernel that a percpu area is always available.
>> The plan is to allocate and keep percpu areas for cpus which have 
>> ever been up.  There'll be no taking down of percpu areas.  
>> Conversion from possible to has_ever_been_up should be much easier 
>> than possible -> online.  State keeping will work fine too.
> 
> That sounds like a very sane plan.
> 
> 	Ingo

Yes, percpu area dynamic *de*-allocation would almost certainly be a
nightmare.

	-hpa

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