Today’s agenda High-level memory management (additional materials + Ch10, Module VIII) page replacement algorithms CS354-Fall2018

Recap: Demanding paging Bring a page into memory only when it is needed Page fault: If there is a reference to a page, first reference to that page will trap to operating system: page fault (interrupt raised by MMU) Operating system to decide: Invalid reference  abort Just not in memory Get empty frame Case I: if there is a free frame Case II: if there is no frame frames (page replacement) Swap page into frame Reset tables Set validation bit = v 5.Restart the instruction that caused the page fault CS354-Fall2018

Recap: Page replacement select a victim frame when there is no free frames Goal: want lowest page-fault rate Algorithms: FIFS Belady’s Anomaly: more frames  more page faults (in-class example: 3 frames vs 4 frames) CS354-Fall2018