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

2. 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

3. 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