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SubjectRe: [Bug #11342] Linux 2.6.27-rc3: kernel BUG at mm/vmalloc.c - bisected
Ingo Molnar wrote:
> * Linus Torvalds <torvalds@linux-foundation.org> wrote:
>
>> On Mon, 25 Aug 2008, Linus Torvalds wrote:
>>> checkstack.pl shows these things as the top problems:
>>>
>>> 0xffffffff80266234 smp_call_function_mask [vmlinux]: 2736
>>> 0xffffffff80234747 __build_sched_domains [vmlinux]: 2232
>>> 0xffffffff8023523f __build_sched_domains [vmlinux]: 2232
>>>
>>> Anyway, the reason smp_call_function_mask and friends have such _huge_
>>> stack usages for you is that they contain a 'cpumask_t' on the stack.
>> In fact, they contain multiple CPU-masks, each 4k-bits - 512 bytes - in
>> size. And they tend to call each other.
>>
>> Quite frankly, I don't think we were really ready for 4k CPU's. I'm
>> going to commit this patch to make sure others don't do that many
>> CPU's by mistake. It marks MAXCPU's as being 'broken' so you cannot
>> select it, and also limits the number of CPU's that you _can_ select
>> to "just" 512.
>
> yeah, that's OK i guess - distros can still enable 4K support if they
> wish to. Someone interested in improving the stack footprint situation
> should dust off the max-stack-footprint tracer so that we can catch
> these things in a more structured way.
>
> And i guess the next generation of 4K CPUs support should just get away
> from cpumask_t-on-kernel-stack model altogether, as the current model is
> not maintainable. We tried the on-kernel-stack variant, and it really
> does not work reliably. We can fix this in v2.6.28.
>
> Ingo

I would be most interested in any tools to analyze call-trees and
accumulated stack usages. My current method of using kdb is really
time consuming.

Thanks!
Mike


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