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

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Message-ID: <20090224151512.GA12438@elte.hu>
Date:	Tue, 24 Feb 2009 16:15:12 +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:

> > It's still about this restriction:
> > 
> > +       /*
> > +        * If large page isn't supported, there's no benefit in doing
> > +        * this.  Also, embedding allocation doesn't play well with
> > +        * NUMA.
> > +        */
> > +       if (!cpu_has_pse || pcpu_need_numa())
> > +               return -EINVAL;
> > 
> > This is what makes no sense (why force the static percpu area 
> > into 4K mappings on NUMA).
> 
> No, the first allocator tried is remap allocator which will do 
> the 2MB remapping thing if NUMA.  If not, it gives its way to 
> embedding allocator which only kicks in for pse && !numa.  The 
> 4k thing is just the last resort.  We might as well kill it 
> and make it
> 
>  if (numa)
> 	do remap
>  else
> 	do embed
>  panic if failed
> 
> The 4k thing is the final fallback for cases where pse isn't 
> supported.

ah, ok :-) Then i was confused by that and wanted to see 
something implemented that ... was already there :)

	Ingo
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