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

[KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>]

Hi,

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...


Thanks,
-Kame




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