Thrashing in operating system by Piyush Sunhare

1. Introduction to Thrashing

Thrashing is a condition where the operating system spends more time swapping pages in and out of memory than executing processes.

It leads to severe performance degradation.

Common in systems with high levels of multiprogramming and insufficient physical memory.

2. How Thrashing Happens

Based on the concept of virtual memory.

As processes execute, they trigger page faults when the required data isn't in RAM.

Too many page faults → constant swapping → CPU spends more time on memory management than processing.

3. Causes of Thrashing

High degree of multiprogramming.

Poor locality of reference in programs.

Inadequate memory allocation per process.

Inefficient page-replacement algorithms (e.g., FIFO).

4. Effects of Thrashing

Drastic decrease in CPU utilization.

Increased response and execution time.

System may freeze or become unresponsive.

Wastes disk bandwidth and processing resources.

5. Detection of Thrashing

Monitor CPU utilization trends—sudden drop indicates possible thrashing.

Analyze page-fault frequency (PFF)—excessive rate implies frequent swapping.

6. Prevention and Solutions

Reduce the number of active processes.

Implement better memory management policies.

Use efficient page-replacement algorithms like Least Recently Used (LRU).

Allocate more memory dynamically to demanding processes.

7. Working Set Model

Defines the set of pages actively used by a process over a time window.

Ensures that only processes with sufficient memory are allowed to continue.

Prevents memory overcommitment and reduces thrashing risk.

8. Page-Fault Frequency (PFF) Strategy

Sets thresholds for acceptable page-fault rates.

If a process exceeds the limit, reduce its memory or suspend it.

If within limits, allocate more memory if available.

9. Real-World Relevance

Operating systems like Windows and Linux implement thrashing detection strategies.
Proper tuning of virtual memory is essential in high-load systems like servers.

10. Conclusion

Thrashing is a serious performance issue tied to virtual memory management.

Effective detection and prevention techniques can ensure stable system operation.

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