tuning GC trigger conditions

[tiancaiamao]

Ref https://arxiv.org/pdf/2204.10455

[tiancaiamao]

Summary:

reserve = inuse + k * sqrt( inuse * allocRate / recycleRate)

allocRate = allocation size / duration
recycleRate = marked size / duration

k is the parameter specified by user, for balancing memory usage and CPU

smooth for inuse, allocRate, recycleRate:

avg = (0.85~0.95) * avg + (1- 0.85~0.95) * new

avoid jitter for reserve:

reserve = (0.8~0.9) * reserve + (1 - 0.8~0.9) * new