We survey basic garbage collection algorithms, and variations such as incremental and generational collection; we then discuss low-level implementation considerations and the relationships between storage management systems, languages, and compilers. Throughout, we attempt to present a uni ed view based on abstract traversal strategies, addressing issues of conservatism, opportunism, and immediacy of reclamation; we also point outavariety of implementation details that are likely to have a significant impact on performance.

Locality of reference is crucial to the performance of modern computers, but is actually poorly understood. In this paper, we survey issues in locality and memory hierarchy design, attempting to bring together what is known, correct common misconceptions, and clarify what is not known. We present a unified approach to locality, based on the concept of timescale relativity, which simply says that some patterns in program behavior are relevant to issues of caching, and others are not, and that the difference depends crucially on the timescale relevant to a particular cache. Memory hierarchies use a kind of online, adaptive algorithm to control caching; such algorithms cannot be studied properly without some understanding of the regularities in the "data" (program behavior) they must process. We attempt a vertical unification, showing that locality of reference results from regularities in the structure of programs, and from regularities in how memory allocators map program objects ont...