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Add "used" to least recent (LRU) in virtual memory #114

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Add "used" to least recent (LRU) in virtual memory #114

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4 changes: 2 additions & 2 deletions content/vm/page-table.md
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Expand Up @@ -70,7 +70,7 @@ A page's location is determined by accessing the page table for the physical pag

:::{note} Page Replacement Policy
:class: dropdown
Almost all virtual memory systems try to replace the **least recently (LRU)**[^lru] page to maximize temporal locality. As mentioned earlier, the overriding guideline is to minimize page faults. Relative to the cost of a page fault, the cost of software and hardware to maintaining data for least recently used pages is small.
Almost all virtual memory systems try to replace the **least recently used (LRU)**[^lru] page to maximize temporal locality. As mentioned earlier, the overriding guideline is to minimize page faults. Relative to the cost of a page fault, the cost of software and hardware to maintaining data for least recently used pages is small.

[^lru]: To be precise, from _Computer Architecture_, Appendix B: "many processors provide a _use bit_ or _reference bit_, which is logically set whenever a page is accessed. ... The operating system periodically clears the use bits and later records them so it caan determine which pages were touched during a time period. By keeping track in this way, the operating system can select a page that is among the least recently reference."
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Expand Down Expand Up @@ -235,4 +235,4 @@ Watch the lecture video below. See CS 152 and CS 152 for more details, or these
:title: "[CS61C FA20] Lecture 30.1 - Virtual Memory II: Hierarchical Page Tables"
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