ch09内存管理.ppt

Chapter 9: Memory Management
内存是计算机系统的最重要的资源之一。
为提高响应速度及CPU的利用率,必须将多个进程同时放入内存,多进程共享内存。
本章介绍内存管理方法。内存管理方法很多,但内容主要涉及下述三个方面:
内存分配回收方法
地址映射和重定位
内存保护
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内存管理
本章讨论内存管理的各种方案,内存管理算法在不同的系统中有不同的方案,每种方案有自己的优点与缺点,选择某种方案取决于多种因素,尤其依赖于系统的硬件设计因素。
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本章内容
Background(背景)
Logical versus Physical Address Space(逻辑与物理地址空间)
Swapping (交换)
Contiguous Allocation(连续分配)
Paging(分页)
Segmentation(分段)
Segmentation with Paging(段页式)
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Background
Program must be brought into memory and placed within a process for it to be executed.(程序必需装入内存,并为其创建内存才能被执行)
Input queue – collection of processes on the disk that are waiting to be brought into memory for execution.(输入队列—磁盘上等待进入内存并执行的进程的集合)
User programs go through several steps before being executed. (用户程序在执行之前必需经历很多步骤装入、地址映射、重定位)
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Binding of Instructions and Data to Memory
Address binding of instructions and data to memory addresses canhappen at three different stages.
(内存地址联编可以在三个不同的阶段发生。)
教材中用捆绑。
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指令与地址联编
Compile time(编译时期): If memory location known a priori, absolute code can be generated; must pile code if starting location changes.(如果内存位置已知,可生成绝对代码;如果开始位置改变,需要重新编译代码)
Load time(装入时期): Must generate relocatable code if memory location is not known pile time.(如果存储位置在编译时不知道,则必须生成可重定位代码)
Execution time(执行时期): Binding delayed until run time if the process can be moved during its execution from one memory segment to another. Need hardware support for address maps (., base and limit registers). (如果进程在执行时可以在内存中移动,则地址绑定要延迟到运行时。需要硬件对地址映射的支持,例如基址和限长寄存器)
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Dynamic Loading动太装入
Routine is not loaded until it is called.(程序在调用之前并不执行)
Better memory-space utilization; unused routine is never loaded.(更好的内存空间利用率;没有被使用的程序不被载入。)
Useful when large amounts of code are needed to handle infrequently occurring cases.(当需要大量的代码来处理不经常发生的事情时是非常有用的。)
No special support from the operating system is required implemented through program design.(不需要操作系统的特别支持,通过程序设计实