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Faults, victims, and thrashing

Computing · Computer Systems · ages 20-21

Name ______________________ Date ____________

In the taught model, two frames are full and an absent page is requested. How is room made?
- Count a hit and keep the existing pages
- Load it into either occupied frame without replacing anything
- Evict a resident victim and reuse its frame
Which access can cause a recoverable missing-page fault?
- Access to a valid page absent from RAM
- A permitted read from a resident page
- A write to a resident page with read-only permission
Which observation best fits thrashing?
- A program waits for input with no paging
- Frequent page transfers and little execution progress
- Heavy file copying while program pages remain resident
Start with two empty frames. For references 1, 2, 1, 3, 1, 2, how many FIFO faults occur, and which rule matters?
- 4; a hit refreshes the page's arrival order
- 3; initial loads into empty frames do not count
- 5; hits leave arrival order unchanged
Start with two empty frames. For references 1, 2, 1, 3, 1, 2, how many faults occur under LRU?
Answer: ______________
For a known finite trace, optimal replacement evicts a resident page used farthest in the future, including one never used again.
Circle one: True False
Logging only past references lets a kernel guarantee optimal replacement for every possible future.
Circle one: True False
Sam says LRU always has fewer faults than FIFO. With two empty frames and references 8, 9, 8, what disproves the claim?
- LRU has 1 fault because the repeat removes an earlier fault
- Both have 2 faults; a tie disproves 'always fewer'
- FIFO has 0 faults because all distinct pages fit

Answer key

For grown-ups. Fold this page away before handing over the rest.

Faults, victims, and thrashing W1-mt_nEEuGL89Ze-s1

Evict a resident victim and reuse its frame · Two frames cannot hold three distinct pages in this model. A victim leaves before its frame receives the requested page.
Access to a valid page absent from RAM · The valid nonresident page needs missing-page recovery. A permitted resident read does not. The write to a read-only resident page violates permissions instead.
Frequent page transfers and little execution progress · Thrashing combines repeated paging with poor execution progress. Storage activity from copying files is not enough to identify it.
5; hits leave arrival order unchanged · The hit on 1 leaves it oldest. Then 3 evicts 1, 1 evicts 2, and 2 evicts 3: five faults total.
4 · The references produce fault, fault, hit, fault, hit, fault: four faults.
True · The offline rule protects pages needed sooner. A page never used again has no later reference to miss.
False · Identical pasts can have different futures requiring different victims. Past logs alone do not supply future references.
Both have 2 faults; a tie disproves 'always fewer' · Both load 8 and 9 with faults, then hit on 8. The equal totals contradict strictly fewer faults on every trace.