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Date: Wed, 18 Jul 2007 19:32:32 +0200
From: Rene Herman <rene.herman@gmail.com>
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To: Phillip Susi <psusi@cfl.rr.com>
CC: Matt Mackall <mpm@selenic.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...?
References: <200707111916.35036.jesper.juhl@gmail.com> <2c0942db0707112159v3ee2cd83i74759c7138e273f7@mail.gmail.com> <9a8748490707121324q3b3e6e65ye14ab8e7f089d999@mail.gmail.com> <4696C89E.4010002@goop.org> <9a8748490707121925w5fb22c0o61068f06d66d5845@mail.gmail.com <20070714191737.GA11166@waste.org> <469E4BB0.8010203@cfl.rr.com>
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On 07/18/2007 07:19 PM, Phillip Susi 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.

As far as I'm aware that's just a consequence of the way linux does memory 
management. If we ignore highmem, virtual memory is simply +/- PAGE_OFFSET 
away from physical so allocating virtually contiguous pages that are _not_ 
physically contiguous requires mapping them somewhere (the vmalloc area) 
which is limited. Given that large number of threads _are_ the problem you 
wouldn't solve things -- you'd again be out of space, although now for a 
different reason.

Rene.