linux-kernel - Re: x86: 4kstacks default

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Message-ID: <20080420133857.GB26536@1wt.eu>
Date:	Sun, 20 Apr 2008 15:38:57 +0200
From:	Willy Tarreau <w@....eu>
To:	Mark Lord <lkml@....ca>
Cc:	Andi Kleen <andi@...stfloor.org>, Adrian Bunk <bunk@...nel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Shawn Bohrer <shawn.bohrer@...il.com>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Arjan van de Ven <arjan@...radead.org>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: x86: 4kstacks default

On Sun, Apr 20, 2008 at 09:27:32AM -0400, Mark Lord wrote:
> Willy Tarreau wrote:
> >
> >What would really help would be to have 8k stacks with the lower page
> >causing a fault and print a stack trace upon first access. That way,
> >the safe setting would still report us useful information without
> >putting users into trouble.
> ..
> 
> That's the best suggestion from this thread, by far!
> Can you produce a patch for 2.6.26 for this?

Unfortunately, I can't. I wouldn't know where to start from.

> Or perhaps someone else here, with the right code familiarity, could?

I hope so.

> Some sort of CONFIG option would likely be wanted to
> either enable/disable this feature, of course.

If we want to migrate to 4k sooner or later, this behaviour would not
need a config option, maybe just a /proc or /sys tunable to disable
the warning. Config would be either (4k + risk of crash) or (8k + warning).

The *real* issue is to decide whether we need/want 4k or not, because
I think we're still discussing the subject for no reason, as usual...

Willy

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