文档介绍：Operating System
Lecture Six
Virtual Memory
School of Software
Nanjing University
1
本主题教学目标
了解虚拟存储管理的基本特点
掌握页式虚拟存储管理
掌握段式虚拟存储管理
掌握页面调度策略与算法
了解pentium的地址转换机构
2
Virtual Memory
Introduction to VM
Paging
Segmentation
OS Software for Paging
Pentium Example
3
Hardware and Control Structures
Memory references are dynamically translated into physical addresses at run time
A process may be swapped in and out of main memory such that it occupies different regions
A process may be broken up into pieces that do not need to located contiguously in main memory
All pieces of a process do not need to be loaded in main memory during execution
4
Execution of a Program
OS brings into main memory a few pieces of the process
Resident set - portion of process that is in main memory
An interrupt is generated when an address is needed that is not in main memory
Piece of process that contains the logical address is brought into main memory automatically
OS issues a disk I/O Read request
OS places the process in a blocking state
Another process is dispatched to run while the disk I/O takes place
An interrupt is issued when disk I/plete which causes the OS to place the affected process in Ready
5
Advantages of Breaking up a Process
More processes may be maintained in main memory
Only load in some of the pieces of each process
With so many processes in main memory, it is very likely a process will be in the Ready state at any particular time
A process may be larger than all of main memory
6
Types of Memory
Real memory
Main memory
Virtual memory
Memory on disk
Allows for effective multiprogramming and relieves the user of tight constraints of main memory
7
Principle of Locality
Program and data references within a process tend to cluster
Only a few pieces of a process will be needed over a short period of time
Possible to make intelligent guesses about which pieces will be needed in the future
This suggests that virtual memory may work efficiently
8
Principle of Localit