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    SubjectRe: VM balancing issues on 2.6.13: dentry cache not getting shrunk enough
    Manfred Spraul <manfred@colorfullife.com> wrote:
    >
    > One tricky point are directory dentries: As far as I see, they are
    > pinned and unfreeable if a (freeable) directory entry is in the cache.
    >

    Well. That's the whole problem.

    I don't think it's been demonstrated that Ted's problem was caused by
    internal fragementation, btw. Ted, could you run slabtop, see what the
    dcache occupancy is? Monitor it as you start to manually apply pressure?
    If the occupancy falls to 10% and not many slab pages are freed up yet then
    yup, it's internal fragmentation.

    I've found that internal fragmentation due to pinned directory dentries can
    be very high if you're running silly benchmarks which create some
    regular-shaped directory tree which can easily create pathological
    patterns. For real-world things with irregular creation and access
    patterns and irregular directory sizes the fragmentation isn't as easy to
    demonstrate.

    Another approach would be to do an aging round on a directory's children
    when an unfreeable dentry is encountered on the LRU. Something like that.
    If internal fragmentation is indeed the problem.
    -
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