操作系统原理9new

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1、Chapter9:VirtualMemory沈卓炜zwsh@hen@seu.eddu.cn九龙湖校区计算机楼347房间52090919CCapte9hapter9:VirtuaeoytualMemory¢Background¢DemandPaging¢Copy-on-Write¢PageReplacement¢AllocationofFrames¢Thrashing¢Memory-MappedFiles¢AllocatingKernelMemoryAllocatingKernelMemory¢OtherConsiderations¢Operating-Sys

2、temExamplesOperatingSystemConcepts9.2SoutheastUniversityBackground¢VitVirtualmemory–separationofuserlogicalmemoryfromphysicalmemory.©Onlypartoftheprogramneedstobeinmemoryforeeecutoxecution.©Logicaladdressspacecanthereforebemuchlargerthanphysicaladdressspacelargerthanphysicaladdress

3、space.©Moreprogramscanberunatthesametime©LessI/ObI/Obeneedddtledtoloadorswap¢Virtualmemoryypcanbeimplementedvia:©Demandpaging©DemandsegmentationDemandsegmentationOperatingSystemConcepts9.3SoutheastUniversityVirtualMemoryThatisLargerThanPhysicalMemoryOperatingSystemConcepts9.4Southe

4、astUniversityVirtual-addaddessSpaceressSpaceOperatingSystemConcepts9.5SoutheastUniversityCCapte9hapter9:VirtuaeoytualMemory¢Background¢DemandPaging¢Copy-on-Write¢PageReplacement¢AllocationofFrames¢Thrashing¢Memory-MappedFiles¢AllocatingKernelMemoryAllocatingKernelMemory¢OtherConsid

5、erations¢Operating-SystemExamplesOperatingSystemConcepts9.6SoutheastUniversityDemandPaging¢Bringapageintomemoryonlywhenitisneeded.©LessI/Oneeded©Lessmemoryneeded©Fasterresponse©Moreusers¢PageisneededPageisneeded⇒referencetoitreferencetoit©invalidreference⇒abort©not-in-memory⇒bringt

6、omemory¢PuredemandpagingPuredemandpaging–neverbringapageneverbringapageintomemoryunlesspagewillbeneededOperatingSystemConcepts9.7SoutheastUniversityVaadlid-InvaadtlidBit¢WitheachpagetableentraalidWitheachpagetableentryavalid–inalidbitinvalidbitisassociated(1⇒in-memory,0⇒not-in-memo

7、ry)¢InitiallyvalidInitiallyvalid–invalidbitissetto0onallinvalidbitissetto0onallentries.¢DiDuringaddresstransltilation,ifvalid–invalidbitlidbitinpagetableentryis0⇒pagefault.OperatingSystemConcepts9.8SoutheastUniversityPageTableWhenSomePagesAreNotinMainMemoryOperatingSystemConcepts9.

8、9SoutheastUniversityPageFa