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

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Message-ID: <20090625195408.GW6760@one.firstfloor.org>
Date:	Thu, 25 Jun 2009 21:54:08 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Tejun Heo <tj@...nel.org>, linux-kernel@...r.kernel.org,
	x86@...nel.org, linux-arch@...r.kernel.org, mingo@...e.hu,
	tglx@...utronix.de, cl@...ux-foundation.org
Subject: Re: [PATCHSET] percpu: generalize first chunk allocators and improve lpage NUMA support

On Thu, Jun 25, 2009 at 07:18:07AM -0700, H. Peter Anvin wrote:
> Andi Kleen wrote:
> >>>
> >> *Ahem* virtual machines *ahem*...
> > 
> > And? Even there's not that big typically. 
> > 
> > The traditional problem was just for 128 NR_CPUs kernel were nothing
> > was sized based on machine capacity.
> > 
> > Also on large systems the VMs shouldn't be sized for full capacity.
> > 
> 
> We have already have cases where the "possible" CPUs have eaten up the
> entire vmalloc area on 32 bits.  In real use.  It's a real problem.

That's hard to believe or a serious bug/misconfiguration somewhere. 

Each per CPU data should be <100k (let's say 200k with some slack for modules), 
so to fill vmalloc you would need hundreds of CPUs, which a 32bit
kernel doesn't really support anyways because it doesn't support
enough memory for that many CPUs.

Perhaps you had firmware/hypervisor who passed a gigantic impossible
value here? If yes thy

-Andi

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