Passivation of clustered HttpSessions works by evicting the node tree representing a given session from the cache. Configuration is based on defining how many active (in-memory) sesssion are allowed and how old they can be before passivating them. Problem is, with FIELD replication, the bulk of the data associated with a session is not in that sessions's subtree; it's in the JBossInternal area. Evicting the session's tree doesn't free up the memory associated with the POJOs.

Structure of data in JBC:

/JSESSION
+++ /localhost
++++++/webapp
+++++++++/session12345
+++++++++/session67890
+++++++++/JBossInternal
++++++++++++/pojoAAAAA
++++++++++++/pojoBBBBB

(Note: session passivation is not done using the regular JBC eviction algorithms, as JBC doesn't understand what a "session" is. The http session replication layer manages the passivation, just using the JBC evict() method to do the actual passivation.)