Page Replacement
Page replacement is performed independently for each page zone
- Algorithm is a variant of the clock page-replacement algorithm
- Two linked lists per zone
- Active list contains pages that have been referenced recently
- Inactive list contains pages that have been used less recently
- Page enters system at the head of the inactive list, referenced bit set
- If the page is active or inactive and its referenced bit is off, the bit is turned on
- Ensures that recently referenced pages are not selected for replacement
- If page is inactive and is being referenced for the second time (referenced bit is on), page is moved to head of the active list, referenced bit is cleared
- Allows the kernel to distinguish between referenced pages that have been accessed once and those that have been accessed more than once recently
- The latter are placed in the active list so they are not selected for replacement
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