linux-kernel - Re: [PATCHSET x86/core/percpu] improve the first percpu chunk allocation

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Date:	Tue, 24 Feb 2009 23:40:43 +0900
From:	Tejun Heo <tj@...nel.org>
To:	Ingo Molnar <mingo@...e.hu>
CC:	rusty@...tcorp.com.au, tglx@...utronix.de, x86@...nel.org,
	linux-kernel@...r.kernel.org, hpa@...or.com, jeremy@...p.org,
	cpw@....com, nickpiggin@...oo.com.au, ink@...assic.park.msu.ru
Subject: Re: [PATCHSET x86/core/percpu] improve the first percpu chunk	allocation

Hello, Ingo.

Ingo Molnar wrote:
> * Tejun Heo <tj@...nel.org> wrote:
> 
>>> and i think that abstraction is wrong.
>> No, it's not wrong.  It simply is irrelevant - it's congruent 
>> vs. contiguos and all that we need is congruent.  Contiguous 
>> of course achieves congruent but it doesn't make any 
>> difference for this purpose.
> 
> Well, as long as we can go up in unit size to 2MB (on 64-bit 
> x86) i'm fine with that model.

Yeap, it defintely can.

> There's no granularity artifacts, right? pcpu_populate_chunk() 
> intelligently only populates pages on an as-needed basis, so 
> extending the percpu areas with a 2MB unit does not trigger 
> nr_cpus*2MB allocations straight away.

Yeap, it doesn't although reclamation is done per-chunk currently.

> The code looks very clean and if we can agree on the SMP/NUMA 
> symmetry and the dynamic-ptr optimizations that it allows, plus 
> if you can up the unit size to 2MB on 64-bit x86, i'm a happy 
> camper and will pull it.

Sounds good.  Thanks.

-- 
tejun
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