31-MemoryPageReplacement - CS 241 Spring 2008 System...

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CS 241 Spring 2008 System Programming 1 Memory Replacement Policies Stallings 8.1,8.2 (Ch22) Lawrence Angrave
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2 Demand Paging Example Load M Free frame Page table VM ref fault
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3 Concepts this Lecture Terminology Demand Paging Replacement Issues Replacement Strategies
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4 #1 Terminology Reference string : the memory reference sequence generated by a program. Paging – moving pages to (from) disk Optimal – the best (theoretical) strategy Eviction – throwing something out Pollution – bringing in useless pages/lines
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5 #2 Demand Paging - Paging Policies Fetch Strategies When should a page be brought into primary (main) memory from secondary (disk) storage? Placement Strategies When a page is brought into primary storage, where is it to be put? Replacement Strategies Which page now in primary storage is to be removed from primary storage when some other page or segment is to be brought in and there is not enough room?
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6 #3 Replacement Issues
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Page Replacement Algorithm (review) find a free page frame if free page frame use it otherwise, select a page frame using the page replacement algorithm write the selected page to the disk and update any necessary tables find location of page on disk read the requested page from the disk. restart the user process.
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31-MemoryPageReplacement - CS 241 Spring 2008 System...

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