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    SubjectRe: [PATCH] mm: do not drain pagevecs for mlock
    2012/1/6 Tao Ma <tm@tao.ma>:
    > Hi Kosaki,
    > On 12/30/2011 06:07 PM, KOSAKI Motohiro wrote:
    >>>> Because your test program is too artificial. 20sec/100000times =
    >>>> 200usec. And your
    >>>> program repeat mlock and munlock the exact same address. so, yes, if
    >>>> lru_add_drain_all() is removed, it become near no-op. but it's
    >>>> worthless comparision.
    >>>> none of any practical program does such strange mlock usage.
    >>> yes, I should say it is artificial. But mlock did cause the problem in
    >>> our product system and perf shows that the mlock uses the system time
    >>> much more than others. That's the reason we created this program to test
    >>> whether mlock really sucks. And we compared the result with
    >>> rhel5(2.6.18) which runs much much faster.
    >>>
    >>> And from the commit log you described, we can remove lru_add_drain_all
    >>> safely here, so why add it? At least removing it makes mlock much faster
    >>> compared to the vanilla kernel.
    >>
    >> If we remove it, we lose to a test way of mlock. "Memlocked" field of
    >> /proc/meminfo
    >> show inaccurate number very easily. So, if 200usec is no avoidable,
    >> I'll ack you.
    >> But I'm not convinced yet.
    > Do you find something new for this?

    No.

    Or more exactly, 200usec is my calculation mistake. your program call mlock
    3 times per each iteration. so, correct cost is 66usec.


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