Add hints when memory pools are nearly full
Add hints when memory pools are nearly full

See https://docs.google.com/document/d/1IA26pZ8XsUSnQHZ5bEQ_2-Ihr3GdWH4jr-SW81XtNM8/edit for background.

glyn/jvmkill,glyn/jvmkill,glyn/jvmkill,glyn/jvmkill