Runtime is keeping hold to too much memory
Currently runtime only releases memory to OS when it has more than 4x of the amount used. This leads to heavy memory overuse when process is run using many processes and large nurseries. For example, if process is run on 16 CPUs with each having 32MB nursery, it will use total 512MB allocation area. This will push "release boundary" to the 2GB. If process is ever to allocate that much memory for a short term use, it will never be given back to OS and effectively wasted.
Nursery and other non-growing data areas should be excluded from this multiplier. Runtime should only keep an extra memory proportional to heap allocation.