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

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Date:	Tue, 24 Feb 2009 14:02:12 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Tejun Heo <tj@...nel.org>
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

* 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.

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.

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.

	Ingo
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