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    SubjectRe: Lockless page cache test results

    On Thu, 27 Apr 2006, Nick Piggin wrote:
    > >
    > > Of course, with small files, the actual filename lookup is likely to be the
    > > real limiter.
    > Although that's lockless so it scales. find_get_page will overtake it
    > at some point.

    filename lookup is only lockless for independent files. You end up getting
    the "dentry->d_lock" for a successful lookup in the lookup path, so if you
    have multiple threads looking up the same files (or - MUCH more commonly -
    directories), you're not going to be lockless.

    I don't know how we could improve it. I've several times thought that we
    _should_ be able to do the directory lookups under the rcu read lock and
    never touch their d_count or d_lock at all, but the locking against
    directory renaming depends very intimately on d_lock.

    It is _possible_ that we should be able to handle it purely with just
    memory ordering rather than depending on d_lock. That would be wonderful.

    Of course, we do actually scale pretty damn well already. I'm just saying
    that it's not perfect.

    See __d_lookup() for details.

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      Last update: 2009-11-18 23:46    [W:0.021 / U:5.680 seconds]
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