linux memory management

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1、MemoryManagementofLinuxkernelBarrySong宋宝华MMBackground宋宝华AddressbindingRegistersAddresstranslationHardwareMainDisk(CPU)(MMU-MemoryCacheMemoryStorageManagementUnit)VirtualAddressRealAddressMemoryBusI/Obus!Anaddressusedinaninstructioncanpo

2、intanywhereinthevirtualaddressspaceoftheprocess,itstillmustbeboundtoaphysicalmemoryaddress!Programsaremadeofmodules.Compilersorassemblersthataretranslatingamodule,don’tknowwherethemodulewillbeloadedinthephysicalmemory!PCcontainsavirtualaddressthatmustbetranslatedtoaphysicaladdressbeforeaninst

3、ructionisfetched.Addressesofoperandsarealsovirtualaddressesthatneedtobetranslatedbeforetheoperandisbroughtfromthemainmemory(orcache)ConvertingthelinearaddressLinearaddressLinearaddressconversioninthearchitecture-independentmemorymodelPagingHardwareWithTLBPerformanceCharacteristicsofTLB!Typica

4、lTLB"–Size:8-4,096entries"–Hittime:0.5-1clockcycle"–Misspenalty:10-100clockcycles"–Missrate:0.01-10%"!IfaTLBhittakes1clockcycle,amisstakes30clockcycles,andthemissrateis1%,theeffectivememorycyclerateforpagemapping"–1*0.99+(1+30)X0.01=1.30"–1.30clockcyclespermemoryaccess""MMU:accesspermissionsf

5、orprivileged(kernel)andusermodes!itcanhavedifferentaccesspermissionsforprivileged(kernel)andusermodes.Theaccesspermissionbitscontrolaccesstothecorrespondingmemoryregion.Ifanaccessismadetoanareaofmemorywithouttherequiredpermissions,thenapermissionfaultisraised."Pagefault!Apagefaultisatraptothe

6、softwareraisedbythehardwarewhenaprogramaccessesapagethatisnotloadedinphysicalmemory.-Minor(soft):thepageisloadedinmemoryatthetimethefaultisgenerated,butisnotmarkedinMMUasbeingloadedinmemory.ThepagefaulthandlermerelyneedstomaketheentryforthatpageinMMUpointtothepageinmemoryandindicatethatthepag

7、eisloadedinmemory;itdoesnotneedtoreadthepageintomemory.-Major(hard):thepageisnotloadedinmemoryatthetimeofthefault.ThepagefaulthandlerintheOSneedstofindafreelocation:eitherapageinmemory,oranothernon-freepageinmemory.Oncethespacehasbeenmadeavai