An illustrative embodiment of a computer-implemented method for working set adjustment receives a request to use less heap memory than an original maximum forming a new maximum, and determines whether a garbage collection will move objects in response to the request. Responsive to a determination the garbage collection will move objects, add a first callback triggered by initiation of the garbage collection and invoking a handler for the first callback notifying a memory manager to free objects allocated by balloon. The first callback completes and the garbage collection starts. A handler for a second callback is invoked which notifies the memory manager to allocate balloon objects and frees backing memory to an operating system, the balloon objects consuming an amount of memory space equal to a remaining portion of memory necessary to return to the operating system. Completion of the second call back allows the garbage collection to proceed as usual.