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    SubjectRe: page fault scalability patch V11 [0/7]: overview
    On Fri, Nov 19, 2004 at 09:33:12PM -0600, Robin Holt wrote:
    > Agree, we are currently using atomic ops on a global rss on our 2.4
    > kernel with 512cpu systems and not seeing much cacheline contention.
    > I don't remember how little it ended up being, but it was very little.
    > We had gone to dropping the page_table_lock and only reaquiring it if
    > the pte was non-null when we went to insert our new one. I think that
    > was how we had it working. I would have to wake up and actually look
    > at that code as it was many months ago that Ray Bryant did that work.
    > We did make rss atomic. Most of the contention is sorted out by the
    > mmap_sem. Processes acquiring themselves off of mmap_sem were found
    > to have spaced themselves out enough that they were all approximately
    > equal time from doing their atomic_add and therefore had very little
    > contention for the cacheline. At least it was not enough that we could
    > measure it as significant.

    Also, the densely-packed split counter can only get 4-16 cpus to a
    cacheline with cachelines <= 128B, so there are definite limitations to
    the amount of cacheline contention in such schemes.


    -- wli
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