Re: [2.6 patch] i386: always use 4k/4k stacks

[Arjan van de Ven <arjan@infradead.org>]

On Sun, 2005-12-18 at 13:04 +0100, Stefan Rompf wrote:
> Am Sonntag 18 Dezember 2005 12:21 schrieb Arjan van de Ven:
> 
> > the kernel has a stack overflow detector, which checks at irq entry time
> > if the stack is "rather high" (7kb into the stack on a 8kb stack, 3.5kb
> > on a 4k stack). When this warning hits there's still runway left (like
> > 12.5 percent), but lets say the end becomes in sight. If the stack usage
> > would be really tight, this "early warning" detector would be hitting a
> > lot of people, right?
> 
> Wrong. The probability that an interrupt happens just during the codepath with 
> highest stack usage is very small

so it samples over 1000 times per second, more when busy. Multiplied
over a very large number of users, and 2 years of time. "very small"...
I don't quite agree there.


> Anyway CONFIG_DEBUG_STACKOVERFLOW is not 
> enabled in 2.6.14.4 i386 defconfig. Don't know about vendor kernel kernels 
> though.

the RH/Fedora ones have this enabled

> > (and the "safety net" is a bit of misnomer, since it's not really safe,
> > just "statistically different" if the shit hits the fan)
> 
> If you can't even guarantee that 8k (or 6k) is enough, how can you vote for 4k 
> then ;-) 

it's not 4k it is 4k+4k btw. And my argument is that it's not less
safe.. nor unsafe


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