linux-kernel - Re: x86: 4kstacks default

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Message-ID: <48160FE3.6000401@tmr.com>
Date:	Mon, 28 Apr 2008 13:56:51 -0400
From:	Bill Davidsen <davidsen@....com>
To:	Adrian Bunk <bunk@...nel.org>
CC:	Andi Kleen <andi@...stfloor.org>, Willy Tarreau <w@....eu>,
	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

Adrian Bunk wrote:
> On Sun, Apr 20, 2008 at 03:06:23PM +0200, Andi Kleen wrote:
>> Willy Tarreau wrote:
>> ...
>>> I have nothing against changing the default setting to 4k provided that
>>> it is easy to get back to the save setting
>> So you're saying that only advanced users who understand all their
>> CONFIG options should have the safe settings? And everyone else
>> the "only explodes once a week" mode?
>>
>> For me that is exactly the wrong way around.
>>
>> If someone is sure they know what they're doing they can set whatever
>> crazy settings they want (given there is a quick way to check
>> for the crazy settings in oops reports so that I can ignore those), but
>> the default should be always safe and optimized for reliability.
> 
> That means we'll have nearly zero testing of the "crazy setting" and 
> when someone tries it he'll have a high probability of running into some
> problems.
> 
> Such a "crazy setting" shouldn't be offered to users at all.
> 
> We should either aim at 4k stacks unconditionally for all 32bit 
> architectures with 4k page size or don't allow any architecture
> to offer 4k stacks.
> 
I have suggested before that the solution is to allocate memory in 
"stack size" units (obviously must be a multiple of the hardware page 
size). The reason allocation fails is more often fragmentation than 
actual lack of memory, or so it has been reported.

-- 
Bill Davidsen <davidsen@....com>
   "We have more to fear from the bungling of the incompetent than from
the machinations of the wicked."  - from Slashdot
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