On Thu 19-08-21 16:53:39, yongw.pur@xxxxxxxxx wrote: > From: wangyong <wang.yong@xxxxxxxxxx> > > Inspired by PSI features, vmpressure inotifier function should > also be configured to decide whether it is used, because it is an > independent feature which notifies the user of memory pressure. Yes, it is an independent feature indeed but what is the actual reason to put a more configuration space here. Config options are not free both from the user experience POV as well as the code maintenance. Why do we need to disable this feature. Who can benefit from such a setup? > So we add configuration to control whether vmpressure notifier is > enabled, and provide a boot parameter to use vmpressure notifier > flexibly. Flexibility is nice but not free as mentioned above. > Use Christoph Lamenter’s pagefault tool > (https://lkml.org/lkml/2006/8/29/294) for comparative testing. > Test with 5.14.0-rc5-next-20210813 on x86_64 4G Ram > To ensure that the vmpressure function is executed, we enable zram > and let the program occupy memory so that some memory is swapped out > > unpatched: > Gb Rep Thr CLine User(s) System(s) Wall(s) flt/cpu/s fault/wsec > 2 1 1 1 0.1 0.97 1.13 485490.062 463533.34 > 2 1 1 1 0.11 0.96 1.12 483086.072 465309.495 > 2 1 1 1 0.1 0.95 1.11 496687.098 469887.643 > 2 1 1 1 0.09 0.97 1.11 489711.434 468402.102 > 2 1 1 1 0.13 0.94 1.12 484159.415 466080.941 > average 0.106 0.958 1.118 487826.8162 466642.7042 > > patched and CONFIG_MEMCG_VMPRESSURE is not set: > Gb Rep Thr CLine User(s) System(s) Wall(s) flt/cpu/s fault/wsec > 2 1 1 1 0.1 0.96 1.1 490942.682 473125.98 > 2 1 1 1 0.08 0.99 1.13 484987.521 463161.975 > 2 1 1 1 0.09 0.96 1.09 498824.98 476696.066 > 2 1 1 1 0.1 0.97 1.12 484127.673 465951.238 > 2 1 1 1 0.1 0.97 1.11 487032 468964.662 > average 0.094 0.97 1.11 489182.9712 469579.9842 > > According to flt/cpu/s, performance improved by 0.2% which is not obvious. I haven't checked how are those numbers calculated but from a very brief look it seems like the variation between different runs is higher than 0.2%. Have you checked the average against standard deviation to get a better idea whether the difference is really outside of the noise? -- Michal Hocko SUSE Labs
