| LRU Approximations |
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| • | Aging |
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| – | Keep
a counter for each PTE |
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| – | Periodically
(clock interrupt) – check R-bit |
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| • | If R
= 0 increment counter (page has not been used) |
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| • | If R
= 1 clear the counter (page has been used) |
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| • | Clear
R = 0 |
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| – | Counter
contains # of intervals since last access |
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| – | Replace
page with largest counter value |
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| • | Alternative |
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| – | §4.4.7
in Tannenbaum |
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