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    SubjectRe: [PATCH] mm: do not drain pagevecs for mlock
    On 01/10/2012 07:58 AM, KOSAKI Motohiro wrote:
    > (1/6/12 1:46 AM), Tao Ma wrote:
    >> On 01/06/2012 02:33 PM, KOSAKI Motohiro wrote:
    >>> (1/6/12 1:30 AM), Tao Ma wrote:
    >>>> On 01/06/2012 02:18 PM, KOSAKI Motohiro wrote:
    >>>>> 2012/1/6 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.
    >>>> yes, so mlock can do 15000/s, it is even slower than the whole i/o time
    >>>> for some not very fast ssd disk and I don't think it is endurable. I
    >>>> guess we should remove it, right? Or you have another other suggestion
    >>>> that I can try for it?
    >>> read whole thread.
    >> I have read the whole thread, and you just described that the test case
    >> is artificial and there is no suggestion or patch about how to resolve
    >> it. As I have said that it is very time-consuming and with more cpu
    >> cores, the more penalty, and an i/o time for a ssd can be faster than
    >> it. So do you think 66 usec is OK for a memory operation?
    > I don't think you've read the thread at all. please read akpm's commnet.
    Oh, your patch set doesn't cc to me, so my mail filter moved it to
    another directory..
    Sorry and I will read the whole thread. Thanks again for your time.


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