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    SubjectRe: page fault scalability patch V11 [0/7]: overview
    William Lee Irwin III wrote:
    >> Split counters easily resolve the issues with both these approaches
    >> (and apparently your co-workers are suggesting it too, and have
    >> performance results backing it).

    On Sat, Nov 20, 2004 at 01:18:22PM +1100, Nick Piggin wrote:
    > Split counters still require atomic operations though. This is what
    > Christoph's latest effort is directed at removing. And they'll still
    > bounce cachelines around. (I assume we've reached the conclusion
    > that per-cpu split counters per-mm won't fly?).

    Split != per-cpu, though it may be. Counterexamples are
    as simple as atomic_inc(&mm->rss[smp_processor_id()>>RSS_IDX_SHIFT]);
    Furthermore, see Robin Holt's results regarding the performance of the
    atomic operations and their relation to cacheline sharing.

    And frankly, the argument that the space overhead of per-cpu counters
    is problematic is not compelling. Even at 1024 cpus it's smaller than
    an ia64 pagetable page, of which there are numerous instances attached
    to each mm.

    -- wli
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