[Freeswitch-users] mod_nibblebill and memory problem

Dear All, I'm running mod_nibblebill for my prepaid solution. I still have problem with memory. I have 4 GB RAM and runing debian squeeze 64 bit and 200 calls concurrent Last time nibblebill running with 1 min heartbeat. when i check memory by htop FS user memory 2% anf growth to 60-89% in 8-9 hr. and then FS crash. Now i change hearbeat to 0 it's mean nibble update balance when end of call. but everything are same FS start from 2% and growth to 20% in 2 days. When i unload nibblebill FS running fine. My question is when concurrent calls drop to 1-2 calls why FS (I think nibblebill) still use memory ? something wrong in nibblebill ? BG Dome C.