linux-kernel - Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu areas for other cpus

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Date:	Tue, 22 Sep 2009 18:59:26 -0400 (EDT)
From:	Christoph Lameter <cl@...ux-foundation.org>
To:	Tejun Heo <tj@...nel.org>
cc:	Nick Piggin <npiggin@...e.de>, Tony Luck <tony.luck@...el.com>,
	Fenghua Yu <fenghua.yu@...el.com>,
	linux-ia64 <linux-ia64@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu
 areas for other cpus

On Tue, 22 Sep 2009, Tejun Heo wrote:

>
> +#ifdef	CONFIG_SMP
> +  . = ALIGN(PERCPU_PAGE_SIZE);
> +  __cpu0_per_cpu = .;

__per_cpu_start?

> +  . = . + PERCPU_PAGE_SIZE;	/* cpu0 per-cpu space */
> +#endif

This is a statically sized per cpu area that is used by __get_cpu_var()
Data is access via a cpu specific memory mapping. How does this work when
the area grows beyond  PERCPU_PAGE_SIZE? As far as I can see: It seems
that __get_cpu_var would then cause a memory fault?
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