JBoss memory usage pattern

Taking a look at one of my applications running in a production server, I noticed that there is a "normal but strange" behavior of memory usage.

Let me explain: watching the execution of my JBoss 4.2.2 without any application deployed, I can see that is constantly grows and frees the used heap space, usually a few megabytes in a development server. When I deploy my application, the pattern is the same, but using more memory in average.

Well, in the production server I can see that my JBos开发者_开发问答s, even without any workload, has a minimum memory usage of 1.5GB. Still without any workload, the heap usage grows to 3.6GB, when a minor GC runs and the heap usage comes back to 1.5GB. Every 40s my JBoss grows its heap usage from 1,5GB to 3.6GB, and this pattern repeats indefinitely. When the workload grows, the difference is that the period for growing the memory usage falls to 8s.

So, my question is: is this normal?