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Date: Sun, 20 Apr 2008 09:40:31 -0500
From: Eric Sandeen <sandeen@sandeen.net>
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To: Willy Tarreau <w@1wt.eu>
CC: Mark Lord <lkml@rtr.ca>, Andi Kleen <andi@firstfloor.org>,
       Adrian Bunk <bunk@kernel.org>, Alan Cox <alan@lxorguk.ukuu.org.uk>,
       Shawn Bohrer <shawn.bohrer@gmail.com>, Ingo Molnar <mingo@elte.hu>,
       Andrew Morton <akpm@linux-foundation.org>,
       Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
       Arjan van de Ven <arjan@infradead.org>,
       Thomas Gleixner <tglx@linutronix.de>
Subject: Re: x86: 4kstacks default
References: <20080419145948.GA4528@lintop> <20080420080901.GF1595@cs181133002.pp.htv.fi> <20080420090623.7b173ef1@the-village.bc.nu> <20080420085104.GG1595@cs181133002.pp.htv.fi> <20080420103611.2c0d3519@the-village.bc.nu> <20080420104444.GI1595@cs181133002.pp.htv.fi> <87y778aezh.fsf@basil.nowhere.org> <20080420124717.GH8474@1wt.eu> <480B44C4.4060104@rtr.ca> <480B4EA1.5070305@sandeen.net> <20080420142056.GC26536@1wt.eu>
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Willy Tarreau wrote:
> On Sun, Apr 20, 2008 at 09:09:37AM -0500, Eric Sandeen wrote:
>> 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.
> 
> I thought it was checked only at a few places (eg: during irqs). If so,
> maybe it can miss some call chains ?

Ah, ok I skimmed your first suggestion too quickly.  100% coverage
reports on the initial access to the 2nd 4k that way would be nice.
Well, it would be nice if we all really wanted 4k stacks some day... :)

-Eric