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Date: Wed, 18 Jul 2007 18:32:52 +0100
From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Phillip Susi <psusi@cfl.rr.com>
Cc: Matt Mackall <mpm@selenic.com>, Rene Herman <rene.herman@gmail.com>,
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       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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> 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.