chap41~44存储管理20130407.ppt

n m Hashed Inverted Page Table 页表的结构称为“反向”是因为它使用帧号而不是虚拟页号来索引页表项 使用Hash列表 Memory Management Introduction to Memory Management Fixed Partitioning Dynamic Partitioning Relocation Paging Segmentation 程序的分段结构 分段存储管理引入的主要原因 模块化程序设计的分段结构 分页存储管理一维地址结构 分段存储管理二维地址结构 模块化程序设计的分段结构 子程序段X 数组段A ┇ call [X]∣E (调用X段的入口E) ┇ call [Y]∣F (调用Y段的入口F) ┇ load 1,[A]∣G (调用数组段A[G]) ┇ 主程序段 E：┅┅┅┅┅┅ F：┅┅┅┅┅┅ 子程序段Y G：┅┅┅┅┅┅ 工作区段 Segmentation All segments of all programs do not have to be of the same length There is a maximum segment length Addressing consist of two parts - a segment number and an offset Since segments are not equal, segmentation is similar to dynamic partitioning Segmentation Memory-management scheme that supports user view of memory A program is a collection of segments. A segment is a logical unit such as: main program, procedure, function, method, object, local variables, global variables, common block, stack, symbol table, arrays User’s View of a Program Example of Segmentation Segmentation Architecture Logical address consists of a two tuple: segment-number, offset, Segment table – maps two-dimensional physical addresses; each table entry has: base – contains the starting physical address where the segments reside in memory limit – specifies the length of the segment Segment-table base register (STBR) points to the segment table’s location in memory Segment-table length register (STLR) indicates number of segments used by a program; segment number s is legal if s STLR Segmentation Architecture (Cont.) Protection With each entry in segment table associate: validation bit = 0 ? illegal segment read/write/execute privileges Protection bits associated with segments; code sharing occurs at segment level Since segments vary in length, memory allocation is a dynamic storage-allocation problem A segmentation example is shown in the following diagram Segmentation Hardware Relocation in Segmentation Seg Table Length proc