An object-aware memory architecture

Abstract

Despite its dominance, object-oriented computation has received scant attention from the architecture community. We propose a novel memory architecture that supports objects and garbage collection (GC). Our architecture is co-designed with a Java™ Virtual Machine (JVM™) 1 1 Java and all Java-based marks are trademarks or registered trademarks of Sun Microsystems, Inc., in the United States and other countries. to improve the functionality and efficiency of heap memory management. The architecture is based on an address space for objects accessed using object IDs mapped by a translator to physical addresses. To support this, the system includes object-addressed caches, a hardware GC barrier to allow in-cache GC of objects, and an exposed cache structure cooperatively managed by the JVM. These extend a conventional architecture, without compromising compatibility or performance for legacy binaries. Our innovations enable various improvements such as: a novel technique for parallel and concurrent garbage collection, without requiring any global synchronization; an in-cache garbage collector, which never accesses main memory; concurrent compaction of objects; and elimination of most GC store barrier overheads. We compare the behavior of our system against that of a conventional generational garbage collector, both with and without an explicit allocate-in-cache operation which eliminates many write misses. Our scheme additionally trades L2 misses for in-cache operations, and provides the mapping indirection required for concurrent compaction.