In a virtual machine, Java Virtual Machine, or other runtime environment, a system and a method for improving the garbage collection times of the virtual machine memory. The JVM, or a garbage collector operating therein, can estimate, for an area of the memory space, the sum of the pause times for garbage collection of the software objects within the area, and control the garbage collection process so that the sum of the pause times for garbage collection will be lower than a target pause time limit, with a high degree of probability. A preselected compaction area can be pre-compacted to keep the compaction time within the target limit. The garbage collector can also predict the time required for final marking and repeat precleaning until the predicted final marking time is within the limits for pause times, and can improve pause times by redirecting application worker threads to do garbage collector work when entering or leaving the memory subsystem.