Physical Memory Management in a Network Operating System.

摘要

This dissertation develops and measures methods of using large main memories to provide high performance in a network operating system. The dissertation covers three areas: file caching, virtual memory, and the interaction between the two. The work in all three areas was done as part of Sprite, a new network operating system that is being built here at Berkeley. The first part of the dissertation presents results obtained through the development of the Sprite file system, which uses large main-memory file caches to achieve high performance. Sprite provides non-write-through file caching on both client and server machines. A simple cache consistency mechanism permits files to be shared by multiple clients without danger of stale data. Benchmark programs indicate that client caches allow diskless Sprite workstations to perform within 0-8% of workstations with disks. In addition, client caching reduces server loading by 50% and network traffic by 75%. In addition to demonstrating the performance advantages of client caching, this dissertation also shows the advantage of writing policies that delay the writing of blocks from client caches to server caches and from server caches to disk. A measurement of 9 different writing policies on the client and 4 on the server shows that delayed-write policies provide the best performance in terms of network bytes transferred, disk utilization, server utilization and elapsed time. More restrictive policies such as write-through can cause benchmarks to execute from 25% to 100% more slowly than if delayed-write policies are used. The second part of this dissertation looks at the interaction between the virtual memory system and the file system. It describes a mechanism that has been implemented as part of Sprite that allows the file system cache to vary in size in response to the needs of the virtual memory system and the file system. This is done by having the file system of each machine negotiate with the virtual memory system o