Mostly-Copying Collection: A Viable Alternative to Conservative Mark-Sweep

Abstract. Many high-level language compilers generate C code and then invoke a C compiler to do code generation, register allocation, stack management, and low-level optimization. To date, most of these compilers link the resulting code against a conservative mark-sweep garbage collector in order to reclaim unused memory. Weintroduce a new collector, MCC, based on mostly-copying collection, and characterize the conditions that favor such a collector over a mark-sweep collector. In particular we demonstrate that mostly-copying collection outperforms conservative mark-sweep under the same conditions that accurate copying collection outperforms accurate mark-sweep: Speci cally, MCC meets or exceeds the performance of a mature mark-sweep collector when allocation rates are high, and physical memory is large relative to the live data. 1 High Level Overview Languages such as C [1] and C++ [27] are GC-unfriendly because they allow programs to violate the key premise of tracing garbage collection|that all live objects are reachable by a sequence of pointer traversals from the root set. For example, a program might violate this premise by using pointer arithmetic or casting. Consequently, compilers for GC-unfriendly languages do not support garbage collection and do not provide the information necessary to distinguish pointers from other data. This makes accurate garbage collection infeasible. Conservative tracing garbage collection is a practical memory managemen