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

From mboxrd@z Thu Jan  1 00:00:00 1970
From: Christoph Lameter <cl@linux-foundation.org>
Date: Tue, 22 Sep 2009 22:59:26 +0000
Subject: Re: [PATCH 2/4] ia64: allocate percpu area for cpu0 like percpu
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List-Id: <linux-ia64.vger.kernel.org>
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To: Tejun Heo <tj@kernel.org>
Cc: Nick Piggin <npiggin@suse.de>, Tony Luck <tony.luck@intel.com>, Fenghua Yu <fenghua.yu@intel.com>, linux-ia64 <linux-ia64@vger.kernel.org>, Ingo Molnar <mingo@redhat.com>, Rusty Russell <rusty@rustcorp.com.au>, linux-kernel@vger.kernel.org

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?