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Date: Wed, 18 Jul 2007 13:33:29 -0400
From: Phillip Susi <psusi@cfl.rr.com>
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: Matt Mackall <mpm@selenic.com>, Rene Herman <rene.herman@gmail.com>,
       Jeremy Fitzhardinge <jeremy@goop.org>,
       Jesper Juhl <jesper.juhl@gmail.com>, Ray Lee <ray-lk@madrabbit.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       William Lee Irwin III <wli@holomorphy.com>, David Chinner <dgc@sgi.com>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?
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Alan Cox wrote:
>> Why do the two pages have to be physically contiguous?  The stack just 
>> needs to be two contiguous pages in virtual memory, but they can map to 
>> any two pages anywhere in physical memory.
> 
> Historically we allowed DMA off the stack on old x86 systems. Removing
> that while a good idea would take a lot of auditing. We also have a very
> limited vmalloc window for mapped pages and filling that with stacks
> would be bad.

Wow, DMA off the stack?  That's just crazy.