linux-kernel - Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

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Message-ID: <469E4EB0.4050305@gmail.com>
Date:	Wed, 18 Jul 2007 19:32:32 +0200
From:	Rene Herman <rene.herman@...il.com>
To:	Phillip Susi <psusi@....rr.com>
CC:	Matt Mackall <mpm@...enic.com>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	Ray Lee <ray-lk@...rabbit.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

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.
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