WildFly/JBossAS are java based application servers which runs on top of JRE/JDK so for memory related tuning JVM's tuning is one of the most important part. Also the memory foot print depends on the application which are running on top of that JVM as well. Like the kind of framework which you are using generates More short living objects or more long living objects ...etc.
So i would suggest you to try enabling the GC log first and then check if the GC is happening properly or not and how much heap/PermGen space etc is being used. If needed then a heap dumo also can be collected to find out of any object is consuming more memory unexpectedly. Based on the analysis different tuning can be done at the WildFly/JBoss level as well like Thread Pool tuning, DataSource tuning, EJB Pooling, ...etc which ultimately has impact on overall memory usage.
I searched all the documentation on Jboss 6. There are 12 instances of the word "tuning" of which 0 have to do with any of the tuning you mentioned.
In other words, there no documentation on tuning Jboss 6.
If there IS, please tell me where I can find information on the tuning you mentioned.
Following might help:
For JBossAS 5/6
also I think the Tuning and sliming of previous versions will not completely outdated and helpful.