Big hiccups with ZGC

[Alex Yakushev]

A quick follow up. I think we figured what's going on – there is not 
enough free heap to deal with the allocation rate. You see, we have a 
cache inside the program the size of which was tuned with G1 enabled. 
Apparently, ZGC (and Shenandoah too, got the same problems with it 
today) inflates the size of the cache in bytes (because of the overhead) 
which leaves less breathing room for ZGC/Shenandoah to work. Will try to 
reduce the cache size and come back with the results.