An Implementation of Memory Sharing and File Mapping

Due to demand for shared memory in order to implement databases efficiently, I added the mmap mapped file interface of 4.2 BSD Unix to Sprite, providing shared memory, file mapping, and user-level control over paging. This report first discusses the design issues for a shared memory and file mapping interface and provides an overview of the support for these functions in other operating systems. Details of the Sprite virtual memory system and the changes to support shared memory and file mapping are given. Performance measurements show that in this implementation, mapped files have comparable performance to block I/O and are faster than buffered I/O for sequential access. For random access to locally cached files, the relative performance of mapped files versus block I/O depends on the access patterns. Access to files across the network is limited by network transmission time, both for mapped files and block I/O. January 4, 1993 ############### + The work described here was supported ..