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Page Replacement Policies

Page Replacement Policies - Page Replacement Policies...

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Page Replacement Policies During a page fault for a non-resident page Find an empty page in physical memory If RAM is full, find a page that can be replaced. Load the non-resident page from disk into RAM What page to replace? Two policies: FIFO - First In First Out LRU - Least Recently Used
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FIFO Page Replacement Policy First In First Out. Replace the page that has been in RAM the longest. Example. Assume 3 pages of RAM X X X 1 X X 1 5 X 1 5 3 1 5 3 1 5 3 1 6 5 3 6 1 3 6 1 3 6 1 5 6 1 6 5 VM Pages Referenced: miss miss miss miss miss hit miss hit 2 Hits 6 misses
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LRU Page Replacement Policy Least recently Used. Replace the page that has not been used recently. This is a good predictor of what page will not be used in the short future. X X X 1 X X 1 5 X 1 5 3 1 5 3 1 5 3 1 1 6 3 1 6 3 1 6 3 1 6 5 6 1 6 5 VM Pages
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