METHOD TO CONTROL I/O ACCESSES IN A MULTI-TASKING VIRTUAL MEMORY VIRTUAL MACHINE TYPE DATA PROCESSING SYSTEM

摘要

ABSTRACTA method for accessing information in a page segmented virtualmemory data processing system in which virtual machines runningUNIX type operating systems are concurrently established, and inwhich a memory manager controls the transfer of information betweenprimary and secondary storage devices in response to the occurrenceof page faults.The method establishes a plurality of data structures in a dynamicmanner in response to a Supervisor call to "map" a file. Themapping process assigns a new segment of virtual memory to themapped file and correlates, in one data structure, the virtualaddress of each page of data in the new segment to a disk fileaddress where that page is actually stored.A UNIX system call by an application program for a specific virtualpage is handled by the page fault handler, and not the UNIX kernel,since the application can supply the real address of the page onthe disk file from the data structure that was created by themapped page range Supervisor call.Simple load and store type of instructions are employed for the datatransfer, which avoids much of the overhead that normally accom-panies conventional UNIX read and write system calls to the storagesubsystem.