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    SubjectRe: [patch 1/2] x86,pat Update the page flags for memtype atomically instead of using memtype_lock. -V3
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    On Mon, 2010-03-15 at 06:21 -0700, holt@sgi.com wrote:
    > While testing an application using the xpmem (out of kernel) driver, we
    > noticed a significant page fault rate reduction of x86_64 with respect
    > to ia64. For one test running with 32 cpus, one thread per cpu, it
    > took 01:08 for each of the threads to vm_insert_pfn 2GB worth of pages.
    > For the same test running on 256 cpus, one thread per cpu, it took 14:48
    > to vm_insert_pfn 2 GB worth of pages.
    >
    > The slowdown was tracked to lookup_memtype which acquires the
    > spinlock memtype_lock. This heavily contended lock was slowing down
    > vm_insert_pfn().
    >
    > With the cmpxchg on page->flags method, both the 32 cpu and 256 cpu
    > cases take approx 00:01.3 seconds to complete.

    Acked-by: Suresh Siddha <suresh.b.siddha@intel.com>



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