linux-kernel - Re: x86: 4kstacks default

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Message-ID: <480B4EA1.5070305@sandeen.net>
Date:	Sun, 20 Apr 2008 09:09:37 -0500
From:	Eric Sandeen <sandeen@...deen.net>
To:	Mark Lord <lkml@....ca>
CC:	Willy Tarreau <w@....eu>, 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

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?
> Or perhaps someone else here, with the right code familiarity, could?
> 
> Some sort of CONFIG option would likely be wanted to
> either enable/disable this feature, of course.

Changing the default warning threshold is easy, it's just a #define.
Although setting it too low would spam syslogs on some setups.

When I was trying to cram stuff into 4k in the past, I had a patch which
added a sysctl to dynamically change the warning threshold, and
optionally BUG() when I hit it for crash analysis.  It was good for
debugging, at least.  If something along those lines is desired, I could
resurrect it.

-Eric
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