Chapter 3 memory management

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1、Chapter3MemoryManagementMemoryManagementProgramsexpandtofillthememoryavailabletoholdthem.——Parkinson’sLawMainmemoryisanimportantresourcethatmustbecarefullymanaged.2Memoryhierarchy(分层存储体系)外存(SecondaryStorage)主存(PrimaryStorage)高速缓存(Cache)寄存器(Register)Thefocusofthischapterwillbeontheprogr

2、ammer’smodelofmainmemoryandhowitcanbemanagedwell.3Contents3.1Nomemoryabstraction3.2Amemoryabstraction:addressspaces3.3VirtualMemory3.4Pagereplacementalgorithms3.5Designissuesforpagingsystems3.6Segmentation(分段)43.1NomemoryabstractionEarlymainframecomputers,earlyminicomputers,andearlyper

3、sonalcomputershadnomemoryabstraction.Everyprogramsimplysawthephysicalmemory.Undertheseconditions,itwasnotpossibletohavetworunningprogramsinmemoryatthesametime.5Figure3-1.Threesimplewaysoforganizingmemorywithanoperatingsystemandoneuserprocess.Nomemoryabstraction6Runningmultipleprogramsw

4、ithoutamemoryabstraction(a)A16-KBprogram(b)Another16-KBprogram(c)Thetwoprogramsloadedconsecutivelyintomemory7RunningmultipleprogramswithoutamemoryabstractionTheproblem?Theinstruction“JMP28”inthesecondprogramwilljumptotheADDinstructioninthefirstprogram.Theprogramwillmostlikelycrash.How

5、tosolveit?Staticrelocation(静态重定位):Whenaprogramisloadedataddressa,theconstantaisaddedtoeveryprogramaddressduringtheloadprocess.Butitisnotaverygeneralsolutionandslowsdownloading.83.2Amemoryabstraction:addressspaces(地址空间)Exposingphysicalmemorytoprocesseshasseveralmajordrawbacks:Ifuserpr

6、ogramscanaddresseverybyteofmemory,theycaneasilytrashtheOS.Withthismodel,itisdifficulttohavemultipleprogramsrunningatonce.3.2.1Thenotionofanaddressspace3.2.2Swapping3.2.3ManagingFreeMemory93.2.1ThenotionofanaddressspaceTwoproblemshavetobesolvedtoallowmultipleapplicationstobeinmemoryatth

7、esametimewithouttheirinterferingwitheachother:ProtectionRelocation(重定位)10ThenotionofanaddressspaceAddressspace:thesetofaddressesthataprocesscanusetoaddressmemory.Eachprocesshasitsownaddressspace,independentofthosebelongingtootherprocess.11BaseandLimitRegistersDynamicrelocation(动态重定位)