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

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Message-Id: <E1IA7j1-0000j9-I3@be1.lrz>
Date:	Sun, 15 Jul 2007 19:17:39 +0200
From:	Bodo Eggert <7eggert@....de>
To:	Matt Mackall <mpm@...enic.com>,
	Rene Herman <rene.herman@...il.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...?

Matt Mackall <mpm@...enic.com> wrote:
> On Fri, Jul 13, 2007 at 03:20:54PM +0200, Rene Herman wrote:

>> As far as I'm aware, the actual reason for 4K stacks is that after the
>> system has been up and running for some time getting "1 physically
>> contiguous pages" becomes significantly easier than 2 which wouldn't be
>> arbitrary.
> 
> If there are exactly two free pages in the system, the odds of them
> being buddies (ie adjacent AND properly aligned) is quite small. The
> available page pool has to grow quite a bit before the availability of
> order-1 page pairs approaches 100%.

If there are exactly two free pages in a system, the odds of starting any
program are not very good. You'll have to swap, and if you do, you can swap
two more pages in order to free enough RAM for the stack.
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