In virtual memory management, which condition most effectively prevents thrashing by respecting process working sets?

Introduction / Context:Thrashing occurs when the system spends more time paging than executing, typically because active pages of processes do not fit in physical memory. The working-set model provides a principled way to allocate frames to keep each process's most frequently used pages resident, reducing page faults.

Given Data / Assumptions:

• Demand paging is used with finite physical memory.
• Processes have identifiable working sets that vary over time.
• Replacement and admission policies influence residency.

Concept / Approach:Ensuring that each process's working set is resident stabilizes locality and minimizes fault frequency. Increasing CPU or I/O speed does not address the root cause; the bottleneck is excessive page faults due to insufficient resident locality, not raw compute or I/O throughput.

Step-by-Step Solution:

Verification / Alternative check:After ensuring working sets are resident, CPU utilization rises and page-fault rate drops sharply, confirming thrashing mitigation independent of CPU/I-O speeds.

Why Other Options Are Wrong:

• Increase CPU speed: A faster CPU still stalls on page faults.
• Increase I/O processor speed: Faster I/O helps marginally but does not fix locality mismatch.
• All of the above: Incorrect; only working-set residency tackles the cause.
• None of the above: Incorrect because working-set residency is effective.

Common Pitfalls:Tuning disk hardware without adjusting memory allocation or degree of multiprogramming, which leaves the fundamental locality problem unresolved.

Final Answer:The pages belonging to the working set of the programs are in main memory