Setting memory and GC properties are not really easy and dependent to your application.
- Xms == Xmx will free the JVM to recalculate the memory
will save resources, also the memory is reserved for JBoss ;-)
- MaxPermSize should enough to load your complete App, if the app is complete used direct you will see it after a short time
the perm area is only used for objects that never dies (mostly)
From my experiance a setting ~2-3GB should enough, sometimes if the application is small and the requests fast you might have a better performance without big (stop the world) pauses with less memory.
Good documentation you will find here: