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    SubjectRe: [rfc] lockless pagecache
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    Hi Nick,

    Your patches improve the performance if lots of processes are
    accessing the same file at the same time, right?

    If so, I think we can introduce multiple radix-trees instead,
    which enhance each inode to be able to have two or more radix-trees
    in it to avoid the race condition traversing the trees.
    Some decision mechanism is needed which radix-tree each page
    should be in, how many radix-tree should be prepared.

    It seems to be simple and effective.

    What do you think?

    > Now the tree_lock was recently(ish) converted to an rwlock, precisely
    > for such a workload and that was apparently very successful. However
    > an rwlock is significantly heavier, and as machines get faster and
    > bigger, rwlocks (and any locks) will tend to use more and more of Paul
    > McKenney's toilet paper due to cacheline bouncing.
    >
    > So in the interest of saving some trees, let's try it without any locks.
    >
    > First I'll put up some numbers to get you interested - of a 64-way Altix
    > with 64 processes each read-faulting in their own 512MB part of a 32GB
    > file that is preloaded in pagecache (with the proper NUMA memory
    > allocation).

    Thanks,
    Hirokazu Takahashi.

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