A UNIX Interface for Shared Memory and Memory Mapped Files Under Mach.

Abstract

This paper describes an approach to Unix shared memory and memory mapped files currently in use at CMU under the Mach Operating System. It describes the rationale for Mach's memory sharing and file mapping primitives as well as their impact on other system components and on overall performance. 1. Introduction The 4.2 BSD mapped file interface (mmap) was designed to address two shortcomings of previous Unix systems: a lack of shared memory between processes and the need to simplify processing of file data. Early Unix systems had provided no shared memory access and a stylized way of accessing sequential file data through read and write system calls. Applications that desired random access to data would use Unix's seek operation or buffer their data themselves, often incurring unwanted system overhead. A mapped file facility could allow a user to treat file data as normal memory without regard to buffering or concerns about sequential versus random access. It would also provide an obv...