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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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