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

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Date:	Wed, 23 Sep 2009 09:44:33 -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 Wed, 23 Sep 2009, Tejun Heo wrote:

> On ia64, the first chunk is fixed at PERCPU_PAGE_SIZE.  It's something
> hardwired into the page fault logic and the linker script.  Build will
> fail if the static + reserved area goes over PERCPU_PAGE_SIZE and in
> that case ia64 will need to update the special case page fault logic
> and increase PERCPU_PAGE_SIZE.  The area reserved above is interim
> per-cpu area for cpu0 which is used between head.S and proper percpu
> area setup and will be ditched once initialization is complete.

You did not answer my question.

The local percpu variables are accessed via a static per cpu
virtual mapping. You cannot place per cpu variables outside of that
virtual address range of PERCPU_PAGE_SIZE.

What happens if the percpu allocator allocates more data than available in
the reserved area?

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