Lecture 7: Memory Management
[Pages:27]Lecture7:MemoryManagement
CSE120:PrinciplesofOpera>ngSystems
UCSanDiego:SummerSessionI,2009 FrankUyeda
Announcements
? PeerWiseques>onsduetomorrow. ? Project2isdueonFriday.
? MilestoneonTuesdaynight.
? Homework3isduenextMonday.
2
GoalsforToday
? Mo>va>onforMemoryManagement ? UnderstandPaging
? Howtotranslatefromvirtualtophysicaladdress ? Determinesize,structureofpagetables
3
MemoryManagement
? Goalsofmemorymanagement
? Provideaconvenientabstrac>onforprogramming ? Allocatescarcememoryresourcesamongcompe>ng
processes ? Maximizeperformancewithminimaloverhead
? Mechanisms
? Physicalandvirtualaddressing ? Techniques:Par>>oning,paging,segmenta>on ? Pagetablemanagement,TLBs,VMtricks
? Policies
? Pagereplacementalgorithms
4
Inthebeginning.....
? Batchprogrammedsystems
? Programsusephysical
SP
addressesdirectly ? OSloadsjob,runsit,unloadsit ? Similartowhatnachosdoes
rightnow
(you'llchangethisinProject2)
PC
PhysicalMemory
Stack
Heap DataSegment TextSegment
Opera>ngSystem
5
LettherebeMul>programming
? Mul>programmingchangesallofthis
? Wantmul>pleprocessesinmemoryatonce
? OverlapI/OandCPUofmul>plejobs
? Candoitanumberofways
? Fixedandvariablepar>>oning,paging,segmenta>on
? Requirements
? Needprotec>on?restrictwhichaddressesjobscanuse ? Fasttransla>on?lookupsneedtobefast ? Fastchanges?upda>ngmemoryhardwareoncontext
switch
6
VirtualMemory
? Thebasicabstrac>onprovidedbytheOSmemory managementisvirtualmemory
? Aprocess'saddressspaceinmemoryisnotnecessarily thesameasthephysicalmemory(RAM)addressinwhich itresides
? Whenaprocessrequestsamemoryaddress,theOSwill translatetheaddressfromavirtualaddresstoaphysical address.
7
VirtualAddresses
? Processesaccessmemoryusingavirtualaddress
? ThevirtualaddressisnotthesameasthephysicalRAMaddressinwhichitresides ? TheOS(hardwareMMU)translatesthevirtualaddressintothephysicalRAMaddress ? Whodeterminesthemappingforthetransla>on?
0xFFF.....(EndingAddress) SP
Stack
AddressSpace
Heap
DataSegment
PC 0x00.......(Star>ngAddress)
TextSegment
8
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