Page Replacement (cont)
Factors to consider in deciding which page to replace
- best page is one that won't be used again by its process
- prefer pages that are read-only (no need to write to disk)
- prefer pages that are unmodified (no need to write to disk)
- prefer pages that are used by only one process (see later)
OS can't predict whether a page will be required again by its process
But we do know whether it has been used recently (if we record this)
Useful heuristic: LRU replacement
- a page not used recently may not be needed again soon
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