A mechanism is provided for managing memory of a runtime environment executing on a virtual machine. A balloon agent that is part of a runtime environment is configured to coordinate inflations of a memory balloon within a heap of” the runtime environment and an out-of-heap overflow balloon, particularly in situations where a hypervisor needs to reclaim more memory from the runtime environment than the runtime environment is able to give up. The balloon agent may slowly free out-of-heap balloon memory, which may cause an increase of a target size for the balloon agent, which in turn inflates the memory balloon inside the heap of the runtime environment.