Part 1 Describe the Working Set Page Replacement Algorithm, ensuring that in your explanation, you include a description of the following: - What is the working set, - The working set model and pre-paging, - The use of execution time instead of k most recent references, and the value of tau (t), - Current virtual time and the age of a page, - Explain the 3 parts of the algorithm. Part 2 Suppose that the WSClock page replacement algorithm uses a tau (t) of ten ticks, and the system state is the following: Page Number Time stamp (time of last use) V R M 10 60 1 0 1 11 90 1 1 0 12 90 1 1 1 13 70 1 0 0 14 40 0 0 0 where the three flag bits V, R, and M stand for Valid, Referenced, and Modified, respectively. (a) If a clock interrupt occurs at tick 100 (current virtual time), show the contents of the new table entries. Briefly explain any changes. (You can omit entries that are unchanged.) (b) Suppose that instead of a clock interrupt, a page fault occurs at tick 100 due to a read request to page 14. Show the contents of the new table entries. Explain which page will be evicted, giving the changes made to that page in the table, and explain the changes made to page 14. (You can omit entries that are unchanged.)
Part 1
Describe the Working Set Page Replacement
- What is the working set,
- The working set model and pre-paging,
- The use of execution time instead of k most recent references, and the value of tau (t),
- Current virtual time and the age of a page,
- Explain the 3 parts of the algorithm.
Part 2
Suppose that the WSClock page replacement algorithm uses a tau (t) of ten ticks, and the system state is the following:
|
Page Number |
Time stamp (time of last use) |
V |
R |
M |
|
10 |
60 |
1 |
0 |
1 |
|
11 |
90 |
1 |
1 |
0 |
|
12 |
90 |
1 |
1 |
1 |
|
13 |
70 |
1 |
0 |
0 |
|
14 |
40 |
0 |
0 |
0 |
where the three flag bits V, R, and M stand for Valid, Referenced, and Modified, respectively.
(a) If a clock interrupt occurs at tick 100 (current virtual time), show the contents of the new table entries. Briefly explain any changes. (You can omit entries that are unchanged.)
(b) Suppose that instead of a clock interrupt, a page fault occurs at tick 100 due to a read request to page 14. Show the contents of the new table entries. Explain which page will be evicted, giving the changes made to that page in the table, and explain the changes made to page 14. (You can omit entries that are unchanged.)
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