第七章節(jié)存儲器管理

1、第七章節(jié)存儲器管理第七章節(jié)存儲器管理內(nèi)容提要內(nèi)容提要v存儲器的層次結(jié)構(gòu)v程序執(zhí)行的基礎(chǔ)知識、程序的裝入和鏈接v連續(xù)分配存儲管理方式v分頁存儲管理方式v分段存儲管理v段頁式存儲管理存儲器的層次結(jié)構(gòu)存儲器的層次結(jié)構(gòu)v存儲器是計(jì)算機(jī)系統(tǒng)的重要組成部分容量、價格和速度之間的矛盾內(nèi)存、外存；易失性和永久性內(nèi)存，是稀缺資源v在現(xiàn)代計(jì)算機(jī)系統(tǒng)中，存儲通常采用層次結(jié)構(gòu)來組織多級存儲器結(jié)構(gòu)主存與寄存器高速緩存和磁盤緩存多級存儲器結(jié)構(gòu)多級存儲器結(jié)構(gòu)vStorage systems in a computer system can be organized in a hierarchySpeed, access t

2、imeCost per bitVolatility主存主存 vs. 寄存器寄存器vSame: Access directly for CPURegister nameMemory addressvDifferent: access speedRegister, one cycle of the CPU clockMemory, Many cycles (2 or more)vDisadvantage: CPU needs to stall frequently & this is intolerablevRemedyCache高級緩沖技術(shù)高級緩沖技術(shù)cachingvCachingCop

3、ying information into faster storage systemWhen accessing, first check in the cache, iflIn: use it directlylNot in: get from upper storage system, and leave a copy in the cachevUsing of cachingRegisters provide a high-speed cache for main memoryInstruction cache & data cacheMain memory can be vi

4、ewed as a fast cache for secondary storageMagnetic disks 磁盤磁盤v Transfer time 傳輸時間TT data size * Transfer rateTransfer rate (n M/s)-1 ( n Byte/us )-1 1/n us/Bytev Positioning time 定位時間Seek time 尋道lTsRotational latency 旋轉(zhuǎn)延遲lTRTP Ts +TR m msv TT VS. TPPlease Store data closely 內(nèi)容提要內(nèi)容提要v存儲器的層次結(jié)構(gòu)v程序執(zhí)行的基礎(chǔ)

5、知識、程序的裝入和鏈接v連續(xù)分配存儲管理方式v分頁存儲管理方式v分段存儲管理v段頁式存儲管理程序執(zhí)行的基礎(chǔ)知識程序執(zhí)行的基礎(chǔ)知識vVon Neumann architecture 馮諾依曼體系結(jié)構(gòu)（圖）Program must be brought into memoryMain memory is usually too smallvProcessProgram must be placed within a process for it to be executed作業(yè)池User programslWhere to place the programlseveral steps（圖）地址的

6、類型地址的類型vAbsolute address 絕對地址Address seen by the memory unitPhysical address 物理地址vRelative address 相對地址Linear address 線性地址vLogical address 邏輯地址Generated by the CPUVirtual address 虛擬地址vWhen can the absolute address can be decided?Address binding 地址的綁定地址的綁定Address binding 地址綁定地址綁定, the binding of inst

7、ructions and data to memory, 可以在三種三種時刻進(jìn)行v Compile time If memory location known a priori, absolute code can be generated; must recompile code if starting location changes.v Load time Must generate relocatable code if memory location is not known at compile time.v Execution time Binding delayed until

8、 run time if the process can be moved during its execution from one memory segment to another. Need hardware support for address maps (e.g., base and limit registers)邏輯地址空間和物理地址空間邏輯地址空間和物理地址空間v Logical address space 邏輯地址空間 The set of all logical addresses generated by a programv Physical address spa

9、ce 物理地址空間 The set of all physical addresses corresponding to theses logical addresses v Logical = physical compile-time & load-time address-bindingv logical (virtual) != physical addresses execution-time address-binding MMU (hardware device)Memory-Management Unit (MMU)v Hardware device, 邏輯地址 物理地

10、址v Relocation register 重定位寄存器 Added to every address generated by a user process at the time it is sent to memory E.g. MS-DOS on 80 x86v User program deals with logical addresses, it NEVER sees the real physical addresses.Logical addressPhysical address14346Relocation register14000+MemoryCPUMMU346Dy

11、namic relocation using a relocation register是否需要將進(jìn)程的所有代碼和數(shù)據(jù)一次性裝入？是否需要將進(jìn)程的所有代碼和數(shù)據(jù)一次性裝入？vShall we put the entire program & data of a process in physical memory before the process can be executed?vFor better memory space utilizationDynamic loadingDynamic linkingOverlaysSwapping程序的裝入程序的裝入v絕對裝入方式v可重定

12、位裝入方式v動態(tài)運(yùn)行時裝入方式絕對裝入方式絕對裝入方式v編譯時，產(chǎn)生absolute code，即使用絕對地址的代碼v裝入時，必須裝入到指定的地址v無需對程序和數(shù)據(jù)的地址進(jìn)行修改v適用于單道系統(tǒng)可重定位裝入方式可重定位裝入方式v大多數(shù)情況下，不能預(yù)知裝入地址，只能在裝入時確定v編譯時，產(chǎn)生可重定位代碼，即使用相對地址的代碼v裝入時，必須重定位通常把在裝入時對目標(biāo)程序中指令和數(shù)據(jù)的修改過程稱為重定位。v由于地址變換是在裝入時一次性完成的，以后不再改變，故稱為靜態(tài)重定位v可用于多道系統(tǒng)動態(tài)運(yùn)行時重定位動態(tài)運(yùn)行時重定位v有時候，程序會在內(nèi)存中移動位置例如對換v需要能支持在運(yùn)行過程中動態(tài)改變程序在內(nèi)存

13、中的位置v方法：推遲重定位時機(jī)即從相對地址到絕對地址的轉(zhuǎn)換推遲到程序真正執(zhí)行時才進(jìn)行v因此，裝入內(nèi)存中的代碼和數(shù)據(jù)的地址仍然是相對地址v需要重定位寄存器的支持動態(tài)運(yùn)行時裝入方式動態(tài)運(yùn)行時裝入方式v根據(jù)程序運(yùn)行的局部性，讓程序及其數(shù)據(jù)在需要時才被裝入vBetter memory-space utilization; unused routine is never loaded.vUseful when large amounts of code are needed to handle infrequently occurring casesError routine vNo special s

14、upport from OS is required implemented through program designDue to the users Overlays 覆蓋技術(shù)覆蓋技術(shù)vKeep in memory only those are needed at any given time.vNeeded when process is larger than amount of memory allocated to it.vImplemented by user, no special support needed from OS, programming design of overlay structure is complex程序的鏈接程序的鏈接v多個源程序編譯多個目標(biāo)模塊；庫。需要鏈接成可裝入模塊v根據(jù)鏈接時間的不同靜態(tài)鏈接方式：裝入前很早就鏈接裝入時動態(tài)鏈接：邊裝入，邊鏈接運(yùn)行時動態(tài)鏈接：運(yùn)行時才鏈接靜態(tài)鏈接方式靜態(tài)鏈接方式v靜態(tài)鏈接