Object type directed garbage collection to improve locality

Abstract

Most garbage collected systems have excessive need for RAM to achieve reasonable performance without too much paging. The reason for such poor locality is the way data are organized in the heap. Conventional organization approaches such as breadth-first ordering do not always bring objects in the same active working set together. When such co-active objects are distributed throughout the heap (on different memory pages), high paging costs will result from accessing objects during execution. To alleviate such poor ordering, researchers have tried many different approaches: depth-first ordering, dynamic reorganization, object creation ordering, and hierarchical decomposition. Each of these approaches has its associated costs, effectiveness, and limitations. This paper presents a new ordering approach to improve locality. By paying a little attention to object type and format, effective heuristics can be derived to group co-active objects together. To investigate this idea, a number of such object type directed grouping techniques are incorporated into a Scheme-48 system. Page fault reduction of up to an order of magnitude was observed.