linux-kernel - Re: [PATCH -v2 5/5] x86: use dmi check to treat disabled cpus as hotplug cpus.

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Date:	Thu, 14 Jan 2010 10:25:15 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	Suresh Siddha <suresh.b.siddha@...el.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, Andi Kleen <andi@...stfloor.org>,
	Yinghai Lu <yinghai@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	"ananth@...ibm.com" <ananth@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH -v2 5/5] x86: use dmi check to treat disabled cpus as
	hotplug cpus.

On Wed, Jan 13, 2010 at 02:49:18PM -0800, Suresh Siddha wrote:
> On Wed, 2010-01-13 at 14:36 -0800, H. Peter Anvin wrote:
> > On 01/13/2010 02:29 PM, Suresh Siddha wrote:
> > >>
> > >> Well, that *is* working around broken code, in this case the broken code
> > >> is the percpu allocation strategy.
> > > 
> > > Andi, Recently percpu folks changed the per-cpu static first chunk to
> > > PMD SIZE right. I think that is what causing all this issue.
> > > 
> > 
> > Please don't tell me we're allocating 2 MB per CPU and throwing away
> > most of it...
> 
> Looking at the percpu code, they do seem to free the unused memory in
> that hole.

I took a look at alloc_percpu() at least and it seems to always
allocate for all possible cpus.

Unfortunately we don't have a nice accounting mechanism for it in /proc,
perhaps we should. So it's unclear right now if that is a problem or not.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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