Operating Systems - Thrashing - Working Set Model & Prevention
Trace the sequence of events when a process exceeds its working set size causing thrashing. What happens step-by-step inside the system?
Trace the sequence of events when a process exceeds its working set size causing thrashing. What happens step-by-step inside the system?
easy🧠🧾 Concept Trace Q12 of Q15
Step-by-Step Solution
Step 1: Identify what happens when working set is exceeded
The process causes frequent page faults because its active pages exceed allocated frames.Step 2: OS response
The OS attempts to swap out pages not in the working set to free frames, but if frames are insufficient, thrashing persists.Step 3: Analyze options
A is incorrect because OS cannot always increase frames immediately; thrashing may continue.
B is correct as it describes the OS swapping out pages but thrashing continuing due to frame shortage.
C is incorrect because OS does not ignore page faults.
D is incorrect because load control (reducing processes) is a prevention technique but not an immediate response to page faults.Final Answer:
Option B -> Option BQuick Check:
Thrashing occurs when working set exceeds frames; OS tries to swap but may fail if frames are insufficient.
Quick Trick: Thrashing = page faults + insufficient frames despite swapping
Common Mistakes:
MISTAKES- Assuming OS can instantly allocate more frames
- Believing OS ignores page faults
- Confusing immediate load control with page fault handling
Trap Explanation:
PITFALL- Option A is tempting because it suggests OS fixes thrashing immediately, but thrashing often persists until load control or working set adjustments occur.
Interviewer Note:
CONTEXT- Tests candidate's understanding of the internal sequence during thrashing and OS response.
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