Yousef A. Khalidi

An overview of the Spring system

Spring is a highly modular, distributed, object-oriented operating system. This paper describes the goals of the Spring system and provides overviews of the Spring object model, the security model, and the naming architecture. Implementation details of the Spring microkernel, virtual memory system, file system, and UNIX emulation are supplied.<<ETX>>

Extensible file systems in spring

In this paper we describe an architecture for extensible file systems. The architecture enables the extension of file system functionality by composing (or stacking) new file systems on top of existing file systems. A file system that is stacked on top of an existing file system can access the existing file systems files via a well-defined naming interface and can share the same underlying file data in a coherent manner. We describe extending file systems in the context of the Spring operating system. Composing file systems in Spring is facilitated by basic Spring features such as its virtual memory architecture, its strongly-typed well-defined interfaces, its location-independent object invocation mechanism, and its flexible naming architecture. File systems in Spring can reside in the kernel, in user-mode, or on remote machines, and composing them can be done in a very flexible manner.

Generic support for caching and disconnected operation

Current systems use caching to provide high performance and possibly support disconnected operation. However, current solutions are type specific. With the advent of modular distributed operating systems and mobile machines there is a need to provide generic support for implementing cacheable/disconnectable services. We present an architecture that can be used to implement cacheable/disconnectable services of any type. In addition we present the implementation of this architecture on the Spring operating system. We have used this architecture for implementing file caching and are currently working on other caching implementations and providing support for disconnected operation.<<ETX>>

Virtual memory support for multiple page sizes

The advent of computers with 64-bit virtual address spaces and giga-bytes of physical memory will provide applications with many more orders of magnitude of memory than is possible today. However, to tap the potential of this new hardware, we need to re-examine how virtual memory is traditionally managed. We concentrate in this note on two aspects of virtual memory: software support for multiple page sizes, and memory management policies tuned to large amounts of physical memory. We argue for the need to examine these areas, and we identify several questions that need to be answered. In particular, we show that providing support for multiple page sizes is not as straightforward as may initially appear.<<ETX>>

Caching in an object oriented system

Caching is an important technique for improving performance in distributed systems. However, in general it has been performed on an ad-hoc basis, with each component of the system having to invent its own caching techniques. In the Spring operating system we provide a unified caching architecture that can be used to cache a variety of different kinds of remote objects. For any given kind of object, this architecture lets different client processes within a single machine share a single cache for accessing remote objects. This caching is performed by a separate cacher process on the machine local to client processes, the caching is transparent to the clients, and the cached information is kept coherent. This architecture has been used to implement caching for files and for naming contexts.<<ETX>>