One embodiment of the present invention provides a system that facilitates keeping track of memory usage of tasks in a shared heap. The system operates by performing a garbage collection operation on the shared heap, wherein the garbage collection operation is a compacting garbage collection operation which preserves the ordering of objects within the shared heap. The system determines a memory usage for each task in the shared heap by adding the memory usage for intervals containing objects for each task in the shared heap to the memory usage count for each task to produce an actual memory usage for each task. This garbage collection may or may not be a generational garbage collection operation.