I have application using JSF and run it on wildfly-11.0.0.Final
In my application many sessions are being created. Some last for many hours, most for few seconds only. After some time amount of io.undertow.util.FastConcurrentDirectDeque$Node reaches millions, while i have only hundreds of active sessions.

After analyzing memory dump i found out, that InMemorySessionManager uses deque to create evictionTokens when maxSessions is set. The problem is that each evictionToken has reference to prev and next element from Deque.
The result is one active session can hold references to thousands of empty Deque$Node objects.