Lecture8MemoryManagement:VirtualMemory
ExternalFragmentation:
-Betweenprocesses.
InternalFragmentation
-Insideprocesses
Frame
FixedSizedblockofphysicalmemory
Page
FixedSizedblockoflogicalmemory
PageTable
MapsthePagesontotheFrames.
PageAddress
-PageNumber
-PageOffset.
(Picture1)
(Picture2)
(picture3)
TranslationLook-asideBuffer
AssociativeHighSpeedMemory
highSpeedlookupcache.
DemandPaging
HierarchicalPageTables
Lookupsforthepagetable
Hashed/ClusteredPaging
Hashtableentries,possiblygatherrelatedpages
Inverted
Trackallframesandwhichpagesareassignedtothem
VirtualMemory
LogicalMemoryàManagefileàPhysicalMemory
PageFault
1) makesuretherequestwasvalid
2) ifvalidtraptothekernel
3) findafreeframe
4) readtheframeinfromthedisks,I/O
5) Updatethepagetable
6) Restarttheinstruction.
HowtoImplementVirtualMemory
DemandPaging
-Loadpagesintomemoryonlywhenyouneedthem
PageFault
-Whenyouaccessmemoryanddiscovernopage.
LocalityofReference.