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    SubjectRe: page fault fastpath patch v2: fix race conditions, stats for 8,32 and 512 cpu SMP
    On Tue, Aug 17, 2004 at 08:28:44AM -0700, Christoph Lameter wrote:
    > This is the second release of the page fault fastpath path. The fast path
    > avoids locking during the creation of page table entries for anonymous
    > memory in a threaded application running on a SMP system. The performance
    > increases significantly for more than 4 threads running concurrently.
    > Changes:
    > - Insure that it is safe to call the various functions without holding
    > the page_table_lock.
    > - Fix cases in rmap.c where a pte could be cleared for a very short time
    > before being set to another value by introducing a pte_xchg function. This
    > created a potential race condition with the fastpath code which checks for
    > a cleared pte without holding the page_table_lock.
    > - i386 support
    > - Various cleanups
    > Issue remaining:
    > - The fastpath increments mm->rss without acquiring the page_table_lock.
    > Introducing the page_table_lock even for a short time makes performance
    > drop to the level before the patch.

    Hmm. I'm suspicious but I can't immediately poke a hole in it as it
    leaves most uses of ->page_table_lock in place. I can't help thinking
    there's a more comprehensive attack on the locking in this area, either.

    -- wli
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