JVM Memory & Configuration

A generation in the SAP JVM starts at its initial size, demand then rises above it, and later drops again. What happens to the operating-system memory the VM holds for that generation?

The OS has reserved 2 GB for a generation up to its max, but Java applications are only touching about 800 MB right now. What are the 800 MB, the full reserved 2 GB, and the space not yet reserved each called in SAP JVM terms?

Which VM parameters set the initial and maximum size of the young generation, and which set them for the permanent generation in the SAP JVM?

In the SAP JVM heap, where does a loaded class definition live versus a freshly created object instance versus an object an application has been using for a long time?

You want to enlarge the tenured generation of the SAP JVM. Can you set its initial and max size directly, and if not, which parameters actually determine it?

On the Config Tool Memory tab an admin looks for the parameter -Xmx and cannot find it by that name. Why, and what is it shown as there — plus what is -XX:MaxPermSize called?

In the SAP JVM, who reclaims the memory held by objects that a Java application no longer uses, and why does a large memory demand not by itself put the system at risk?