A garbage collection design and bakeoff in JMTk: An efficient extensible Java memory management toolkit

Abstract

In this paper, we describe the design, implementation, and evaluation of a new garbage collection framework called the Java Memory Management Toolkit (JMTk). The goals of JMTk are to provide an efficient, composable, extensible, and portable toolkit for quickly building and evaluating new and existing garbage collection algorithms. Our design clearly demarcates the external interface between the collector and the compiler for portability. For extensibility, JMTk provides a selection of allocators, garbage identification, collection, pointer tracking, and other mechanisms that are efficient and that a wide variety garbage collection algorithms can compose and share. For instance, our mark-sweep and reference counting collectors share the free list implementation. We perform a comprehensive and detailed study of collectors including copying, mark-sweep, reference counting, copying generational, and hybrid generational collectors using JMTk in Jikes RVM on a uniprocessor. We find that the performance of collectors in JMTk is comparable to the highly tuned original Jikes collectors. In a study of full heap and generational collectors, we confirm the significant benefits of generational collectors on a wide variety of heap sizes, and reveal that on very small heaps, collection time is enormous. These experiments add other new insights, such as firmly establishing that for a variety of generational collectors, a variable-size nursery which is allowed to grow to fill all the space not in use by the older generation performs better than a fixed-size nursery. We thus show the utility of extensive collector comparisons and establish the benefits of our design.