Re: x86: 4kstacks default

Re: x86: 4kstacks default

[Oliver Pinter]

Hi Ingo!

with the older kernel is typical: xfs+nfs+4k stack(+lvm)



On 4/19/08, Ingo Molnar <mingo@elte.hu> wrote:
>
> * Andrew Morton <akpm@linux-foundation.org> wrote:
>
> > >  config 4KSTACKS
> > >  	bool "Use 4Kb for kernel stacks instead of 8Kb"
> > > -	depends on DEBUG_KERNEL
> > >  	depends on X86_32
> > > +	default y
> >
> > This patch will cause kernels to crash.
>
> what mainline kernels crash and how will they crash? Fedora and other
> distros have had 4K stacks enabled for years:
>
>   $ grep 4K /boot/config-2.6.24-9.fc9
>   CONFIG_4KSTACKS=y
>
> and we've conducted tens of thousands of bootup tests with all sorts of
> drivers and kernel options enabled and have yet to see a single crash
> due to 4K stacks. So basically the kernel default just follows the
> common distro default now. (distros and users can still disable it)
>
> 	Ingo
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-- 
Thanks,
Oliver

Re: x86: 4kstacks default

[Adrian Bunk]

On Sat, Apr 19, 2008 at 04:35:31PM +0200, Oliver Pinter wrote:
>...
> with the older kernel is typical: xfs+nfs+4k stack(+lvm)

Does anyone still experience problems with 2.6.25?

We all know that there once were problems, but if there are any left 
they should be reported and fixed.

> Thanks,
> Oliver

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Re: x86: 4kstacks default

[Oliver Pinter]

I dont know, thet this problem presentiert in 2.6.25, but im older
kernels yes (2.6.22> or 2.6.23>).

On 4/19/08, Adrian Bunk <bunk@kernel.org> wrote:
> On Sat, Apr 19, 2008 at 04:35:31PM +0200, Oliver Pinter wrote:
> >...
> > with the older kernel is typical: xfs+nfs+4k stack(+lvm)
>
> Does anyone still experience problems with 2.6.25?
>
> We all know that there once were problems, but if there are any left
> they should be reported and fixed.
>
> > Thanks,
> > Oliver
>
> cu
> Adrian
>
> --
>
>        "Is there not promise of rain?" Ling Tan asked suddenly out
>         of the darkness. There had been need of rain for many days.
>        "Only a promise," Lao Er said.
>                                        Pearl S. Buck - Dragon Seed
>
>


-- 
Thanks,
Oliver

Re: x86: 4kstacks default

[Eric Sandeen]

Adrian Bunk wrote:
> On Sat, Apr 19, 2008 at 04:35:31PM +0200, Oliver Pinter wrote:
>> ...
>> with the older kernel is typical: xfs+nfs+4k stack(+lvm)
> 
> Does anyone still experience problems with 2.6.25?

There are always problems.  You can always come up with something that
will crash in 4k, IMHO.

Rather than foisting this upon everyone, I'd rather see work put into
making stack size a boot parameter or something, so that people can
choose what's appropriate for their workload (or their IO stack, if you
prefer).

-Eric

> We all know that there once were problems, but if there are any left 
> they should be reported and fixed.
> 
>> Thanks,
>> Oliver
> 
> cu
> Adrian
> 

Re: x86: 4kstacks default

[Adrian Bunk]

On Sat, Apr 19, 2008 at 08:56:09PM -0500, Eric Sandeen wrote:
> Adrian Bunk wrote:
> > On Sat, Apr 19, 2008 at 04:35:31PM +0200, Oliver Pinter wrote:
> >> ...
> >> with the older kernel is typical: xfs+nfs+4k stack(+lvm)
> > 
> > Does anyone still experience problems with 2.6.25?
> 
> There are always problems.  You can always come up with something that
> will crash in 4k, IMHO.

We are going from 6k to 4k.

Your "You can always come up with something that will crash in" point 
would be invariant to this change (although it might be harder to 
trigger in real life).

> Rather than foisting this upon everyone, I'd rather see work put into
> making stack size a boot parameter or something, so that people can
> choose what's appropriate for their workload (or their IO stack, if you
> prefer).

Why should users have to poke with such deeply internal things?
That doesn't sound right.

Excessive stack usage in the kernel is considered to be a bug.

We should identify and fix all remaining problems (if any).

> -Eric

cu
Adrian

-- 

       "Is there not promise of rain?" Ling Tan asked suddenly out
        of the darkness. There had been need of rain for many days.
       "Only a promise," Lao Er said.
                                       Pearl S. Buck - Dragon Seed

Re: x86: 4kstacks default

[Chris Wedgwood]

On Sun, Apr 20, 2008 at 10:42:28AM +0300, Adrian Bunk wrote:

> We are going from 6k to 4k.

6k?

> Why should users have to poke with such deeply internal things?
> That doesn't sound right.

they shouldn't, so a 4k default is a problem for them

> Excessive stack usage in the kernel is considered to be a bug.

define excessive

> We should identify and fix all remaining problems (if any).

let's see your patches then

Re: x86: 4kstacks default

[Andi Kleen]

Eric Sandeen <sandeen@sandeen.net> writes:

> Adrian Bunk wrote:
>> On Sat, Apr 19, 2008 at 04:35:31PM +0200, Oliver Pinter wrote:
>>> ...
>>> with the older kernel is typical: xfs+nfs+4k stack(+lvm)
>> 
>> Does anyone still experience problems with 2.6.25?
>
> There are always problems.  You can always come up with something that
> will crash in 4k, IMHO.

But what are a few crashes compared against the ability to run 50000
kernel threads on a 32bit machine? Something has to give in the aim
for useless checkbox numbers after all. 

-Andi