No abstract

Modern object-oriented languages and programming paradigms require finer-grain division of memory than is provided by traditional paging and segmentation systems. This paper describes the design of an OSM (Object Space Manager) that allows partitioning of real memory on object, rather than page, boundaries. The time required by the OSM to create an object, or to find the beginning of an object given a pointer to any location within it, is approximately one memory cycle. Object sizes are limited only by the availability of address bits. In typical configurations of object-oriented memory modules, one OSM chip is required for every 16 RAM chips. The OSM serves a central role in the implementation of a hardware-assisted garbage collection system in which the worst-case stop-and-wait garbage collection delay ranges between 10 and 500 μsec, depending on the system configuration.

In this paper we describe how a profiling system can be successfully used to restructure the components of an operating system for improved overall performance. We discuss our choice of a profiling system and how it was agplied to the AS1400 (Application System1400) operating system for the purpose of reordering code. Previous work in the industry has been mainly useful only for application programs. Our work demonstrates how such techniques can be applied to operating system code, while preserving maintainability of the operating system in the customer's environment. Wopyright 1998 by International Business Machines Corporation. Copying in printed form for private use is permitted without payment of royalty provided that (1) each reproduction is done without alteration and (2) the Journal reference and IBM copyright notice are included on the first page. The title and abstract, but no other portions, of this paper may be copied or distributed royalty free without further permission by computer-based and other information-service systems. Permission to republish any other portion of this paper must be obtained from the Editor.

Hardware-assisted real-time garbage collection offers high throughput and small worst-case bounds on the times required to allocate dynamic objects and to access the memory contained within previously allocated objects. Whether the proposed technology is cost effective depends on various choices between configuration alternatives. This paper reports the performance of several different configurations of the hardware-assisted real-time garbage collection system subjected to several different workloads. Reported measurements demonstrate that hardware-assisted real-time garbage collection is a viable alternative to traditional explicit memory management techniques, even for low-level languages like C++.