virtualmemory - Chapter 9: Virtual Memory Chapter 9:...

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Chapter 9: Virtual Memory Chapter 9: Virtual Memory
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9.2 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Chapter 9: Virtual Memory Chapter 9: Virtual Memory Background Demand Paging Copy-on-Write Page Replacement Allocation of Frames Thrashing Memory-Mapped Files Allocating Kernel Memory Other Considerations Operating-System Examples
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9.3 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Objectives Objectives To describe the benefits of a virtual memory system To explain the concepts of demand paging, page-replacement algorithms, and allocation of page frames To discuss the principle of the working-set model
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9.4 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Background Background Virtual memory – separation of user logical memory from physical memory. Only part of the program needs to be in memory for execution Logical address space can therefore be much larger than physical address space Allows address spaces to be shared by several processes Allows for more efficient process creation Virtual memory can be implemented via: Demand paging Demand segmentation
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9.5 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Virtual Memory That is Larger Than Physical Memory Virtual Memory That is Larger Than Physical Memory
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9.6 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Demand Paging Demand Paging Bring a page into memory only when it is needed Less I/O needed Less memory needed Faster response More users Page is needed reference to it invalid reference abort not-in-memory bring to memory Lazy swapper – never swaps a page into memory unless page will be needed Swapper that deals with pages is a pager
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9.7 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Transfer of a Paged Memory to Contiguous Disk Space Transfer of a Paged Memory to Contiguous Disk Space
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9.8 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Valid-Invalid Bit Valid-Invalid Bit With each page table entry a valid–invalid bit is associated ( v in-memory, i not-in-memory) Initially valid–invalid bit is set to i on all entries Example of a page table snapshot: During address translation, if valid–invalid bit in page table entry is I page fault v v v v i i i …. Frame # valid-invalid bit page table
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9.9 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Page Table When Some Pages Are Not in Main Memory Page Table When Some Pages Are Not in Main Memory
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9.10 Silberschatz, Galvin and Gagne ©2005 Operating System Concepts – 7 th Edition, Feb 22, 2005 Page Fault
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This note was uploaded on 11/15/2011 for the course COMP 3500 taught by Professor Wang,y during the Summer '08 term at Auburn University.

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virtualmemory - Chapter 9: Virtual Memory Chapter 9:...

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