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    SubjectRe: REGRESSION: Performance regressions from switching anon_vma->lock to mutex
    On Fri, Jun 17, 2011 at 4:28 AM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote:
    >
    > Something like so? Compiles and runs the benchmark in question.

    Yup.

    Except I really think that test for a NULL anon_vma should go away.

    If an avc entry has a NULL anon_vma, something is seriously wrong. The
    comment about anon_vma_fork failure is definitely just bogus: the
    anon_vma is allocated before the avc entry, so there's no way a avc
    can have a NULL anon_vma from there.

    But yes, your patch is cleaner than the one I was playing around with
    (your "remove if not list empty" is prettier than what I was toying
    with - having a separate flag in the avc)

    Tim, can you test Peter's (second - the cleaned up one) patch on top
    of mine, and see if that helps things further?

    The only thing I don't love about the batching is that we now do hold
    the lock over some situations where we _could_ have allowed
    concurrency (notably some avc allocations), but I think it's a good
    trade-off. And walking the list twice at unlink_anon_vmas() should be
    basically free.

    Linus


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