操作系统Chapter06-2(New).ppt

6.6 系统举例 Linux存储管理 Windows2000/XP存储管理 6.6.1 Linux存储管理 Physical memory-management Three level page table Buddy algorithm for managing memory pages(frames) Virtual Memory management Demand paging no pre-paging, no working set. Page replacement page daemon: kswapd, runs once a second , keep enough free pages in memory. flush daemon: bdflush, wakes up periodically, “dirty page out”. Managing Physical Memory Allocate ranges of physically-contiguous pages on request. The allocator uses a buddy-heap algorithm to keep track of available physical pages. Each allocatable memory region is paired with an adjacent partner. Whenever two allocated partner regions are both freed up they are combined to form a larger region. If a memory request cannot be satisfied by allocating an existing small free region, then a larger free region will be subdivided into two partners to satisfy the request. Memory allocations time statically: drivers reserve at boot time dynamically (via page allocator). Buddy heap存储分配 64 32 32 32 16 16 8 8 32 16 8 8 req(8) req(8) req(4) rel(8) 32 8 4 4 16 4 rel(8) 32 16 8 8 8 32 8 8 8 32 4 4 8 8 8 8 8 4 4 32 8 Buddy Heap Implementation 9(29) 8(28) 7(27) 6(26) 5(25) 4(24) 3(23) 2(22) 1(21) 0(20) 4 512 256 空闲页面分成10个块组: 编号i=0~9 第i组: 中记载长度为2i 个页面的连续区域. 表示从第256号页面开始, 连续有28=256个页面的块组. 128 64 48 24 8 6.6.2 Windows 2000/XP Memory Management 存储管理 虚拟存储管理器(Virtual Memory Manager :VMM) 负责存储管理 核心: 6 Threads 进程地址空间: 32bits地址=4GB 2GB用户空间,2GB系统空间. PDE PTE Byte 31 22 21 12 11 0 页目录入口 页表入口 页内位移 6.6.2 Windows 2000/XP Memory Management 每页4KB; 地址32位=4B; 1页表=1024项; 进程空间:512个页表;系统空间512个页表; PDE PTE Byte …… …… CR3 + + + 页目录 页表 6.6.2 Windows 2000/XP Memory Management 页面调度 三种状态： 闲置(free)、预定(Reserved)、确认（Committed); 闲置：不存在页面； 确认：已经在内存； 预定：保留内存用； 6.6.2 Windows 2000/XP Memory Management 0 1 …… 511 512 …… k …… 1023 0 1 …… n 0 1 …… 511 512 …… n …… 1023 P2页目录 P1页目录 原型页表 系统页表 P