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

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Date:	Thu, 19 Jul 2007 13:24:36 +0200
From:	Andrea Arcangeli <andrea@...e.de>
To:	Matt Mackall <mpm@...enic.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Rene Herman <rene.herman@...il.com>,
	Ray Lee <ray-lk@...rabbit.org>, Bodo Eggert <7eggert@....de>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jesper Juhl <jesper.juhl@...il.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	David Chinner <dgc@....com>,
	Arjan van de Ven <arjan@...radead.org>
Subject: Re: [PATCH][RFC] 4K stacks default, not a debug thing any more...?

On Wed, Jul 18, 2007 at 08:37:25PM -0500, Matt Mackall wrote:
> Turn on irqstacks when using 8k stacks

Indeed.

> Detect when usage with 8k stacks would overrun a 4k stack when doing
>  our stack switch and do a WARN_ONCE
> Fix up the damn bugs

I don't think they're necessarily bugs. IMHO the WARN_ON is better off
at 7k level like it is today with the current STACK_WARN. 4k for a
stack for common code really is small. I doubt you're going to find
obvious culprits that way, more likely you'll have to mangle the code
to call kmalloc for fairly small structures which isn't necessarily a
good thing in the long term. It comes to mind the folio ptes array
that Hugh allocated on the stack in his large PAGE_SIZE patch of jul
2001, that thing like any other local array, would need to be
kmalloced with a 4k stack. With 4k I'm afraid you better not use the
stack for anything but pointers, especially if you run in common code
that may invoke I/O like that.
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