16-01-2012, 03:11 PM
Virtual-Memory Management
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Objectives
1 To describe the benefits of a virtual memory system
2 To explain the concepts of demand paging, pagereplacement
algorithms, and allocation of page frames
3 To discuss the principle of the working-set model
Background
1Virtual memory – separation of logical memory from
physical memory.
2 Only part of the program needs to be in memory for
execution
3 Logical address space can therefore be much larger
than physical address space
4 Allows address spaces to be shared by several
processes
5 Allows for more efficient process creation
6 Virtual memory can be implemented via:
7 Demand paging
8 Demand segmentation
Copy-on-Write
1 Virtual memory allows benefits during process creation
2 Copy-on-Write (COW) allows both parent and child
processes to initially share the same pages in memory
If either process modifies a shared page, only then is
the page copied
3 COW allows more efficient process creation as only
modified pages are copied
4 Free pages are allocated from a pool of zeroed-out
pages
