linux-kernel - Re: unified percpu stuff

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Date:	Tue, 27 Jan 2009 09:50:58 -0800
From:	Jeremy Fitzhardinge <jeremy@...p.org>
To:	Brian Gerst <brgerst@...il.com>
CC:	Tejun Heo <htejun@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: unified percpu stuff

Brian Gerst wrote:
>> BTW, does the initial cpu0 percpu area get reallocated and moved during
>> boot, or does cpu0 keep using the same memory forever?
>>     
>
> It is reallocated in setup_per_cpu_areas().
>   

Hm, OK.  What's the reason we need to move cpu 0's percpu area?  Its 
always seemed a bit awkward.

Once it has been moved, how can I find the address of a variable in the 
original boot-time cpu 0 percpu area?  There's a couple of pages which 
Xen will have marked RO which need to be made RW if they're being freed 
back into the kernel pool.  Currently I use per_cpu_var(gdt_page), but 
guess that's a small offset rather than a directly usable address.

Thanks,
    J
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