Re: [PATCH v2 1/7] memcg: Scale up vmstats flush threshold with int_sqrt(nr_cpus+2)

[Li Wang]

> > with kernel functions:
> > 	var1 = 65536*nr_cpus / (45426 * ilog2(nr_cpus) + 65536)
> > 	var2 = DIV_ROUND_UP(65536*nr_cpus, 45426 * ilog2(nr_cpus) + 65536)
> > 	var3 = roundup_pow_of_two(var2)


Consider a 1024-CPU machine with a cpuset-constrained cgroup using only 2 CPUs.

Its unavoidable batching error is just 2MB, yet the global threshold imposes
256MB (harmonic-mean) or 32MB (sqrt) of additional error — 128x and 16x
overprovisioning respectively. Both overshoot, but sqrt stays bit closer to
the ideal.

-- 
Regards,
Li Wang