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Date: Mon, 30 Apr 2007 12:49:04 -0700 (PDT)
From: Zwane Mwaikambo <zwane@infradead.org>
Subject: Re: [5/6] dynamically allocate IRQ stacks (was: Re: [-mm patch] i386:
 enable 4k stacks by default)
In-reply-to: <20070430174630.GH19966@holomorphy.com>
To: William Lee Irwin III <wli@holomorphy.com>
Cc: Andi Kleen <andi@firstfloor.org>, Christoph Hellwig <hch@infradead.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, David Chinner <dgc@sgi.com>,
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       Linux Kernel <linux-kernel@vger.kernel.org>
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On Mon, 30 Apr 2007, William Lee Irwin III wrote:

> -static char softirq_stack[NR_CPUS * THREAD_SIZE]
> -		__attribute__((__aligned__(THREAD_SIZE)));
> +static DEFINE_PER_CPU(char *, softirq_stack);
> +static DEFINE_PER_CPU(char *, hardirq_stack);
>  
> -static char hardirq_stack[NR_CPUS * THREAD_SIZE]
> -		__attribute__((__aligned__(THREAD_SIZE)));
> +#ifdef CONFIG_VMALLOC_STACK
> +static void * __init __alloc_irqstack(int cpu)

How about just using DEFINE_PER_CPU and allowing the percpu code 
dynamically allocate.