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    Subject[RFC][PATCH 0/5] memcg: reduce lock conetion

    Recently, memcg's res_counter->lock contention on big server is reported and
    Balbir wrote a workaround for root memcg.
    It's good but we need some fix for children, too.

    This set is for reducing lock conetion of memcg's children cgroup based on mmotm-Aug27.

    I'm sorry I have only 8cpu machine and can't reproduce very troublesome lock conention.
    Here is lock_stat of make -j 12 on my 8cpu box, befre-after this patch series.

    [Before] time make -j 12 (Best time in 3 test)
    real 2m55.170s
    user 4m38.351s
    sys 6m40.694s
    lock_stat version 0.3
    class name con-bounces contentions waittime-min waittime-max waittime-total acq-bounces acquisitions holdtime-min holdtime-max holdtime-total

    &counter->lock: 1793728 1824383 0.90 16599.78 1255869.40 24879507 44909568 0.45 31183.88 19505982.15
    &counter->lock 999561 [<ffffffff81099224>] res_counter_charge+0x94/0x140
    &counter->lock 824822 [<ffffffff8109911c>] res_counter_uncharge+0x3c/0xb0
    &counter->lock 835597 [<ffffffff8109911c>] res_counter_uncharge+0x3c/0xb0
    &counter->lock 988786 [<ffffffff81099224>] res_counter_charge+0x94/0x140

    you can see this by "head" ;)

    [After] time make -j 12 (Best time in 3 test..but score was very stable.)
    real 2m52.612s
    user 4m45.450s
    sys 6m4.422s

    &counter->lock: 11159 11406 1.02 30.35 6707.74 1097940 3957860 0.47 17652.17 1534430.74
    &counter->lock 2016 [<ffffffff810991bd>] res_counter_charge+0x4d/0x110
    &counter->lock 9390 [<ffffffff81099115>] res_counter_uncharge+0x35/0x90
    &counter->lock 8962 [<ffffffff81099115>] res_counter_uncharge+0x35/0x90
    &counter->lock 2444 [<ffffffff810991bd>] res_counter_charge+0x4d/0x110

    dcache-lock, zone->lru_lock etc is much heavier than this.

    I expects good result on big servers.

    But this patch sereis is a "big change". I (and memcg folks) have to be careful...


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