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    SubjectRe: 2.4.23aa2 (bugfixes and important VM improvements for the high end)
    Andrew Morton wrote:
    > We believe that this could cause misbehaviour of such things as the
    > boehm garbage collector. This patch provides the mprotect() atomicity by
    > performing all userspace copies under page_table_lock.

    Can you use a read-write lock, so that userspace copies only need to
    take the lock for reading? That doesn't eliminate cacheline bouncing
    but does eliminate the serialisation.

    Or did you do that already, and found performance is still very low?

    > It is a judgement call. Personally, I wouldn't ship a production kernel
    > with this patch. People need to be aware of the tradeoff and to think and
    > test very carefully.

    If this isn't fixed, _please_ provide a way for a garbage collector to
    query the kernel as to whether this race condition is present.

    -- Jamie
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