Compacting Garbage Collection can be Fast and Simple

Abstract

Copying garbage collectors are now standard for the memory-management subsystems of functional and object-oriented programming languages. Compacting garbage collection has correspondingly fallen out of favor. We revitalize the case for compaction by demonstrating that a simple compacting collector, extended with the generational garbage collection heuristic, exhibits performance as effectively as or better than a well-designed generational copying collector on real programs running in real environments. The observation that compaction preserves allocation order across collections leads to a new generalization of the generational heuristic that reduces the movement of long-lived objects. We measure the effect of substituting our compacting generational collector for a copying collector in Standard ML of New Jersey.