Question

In which one of the following page replacement policies, Belady's anomaly may occur?
1. FIFO
2. Optimal
3. LRU
4. MRU

Answer 1

Correct Answer - Option 1 : FIFO

Belady's anomaly may occur in FIFO

• A page fault occurs when a page is not found in the memory and needs to be loaded from the disk. If a page fault occurs and all memory frames have been already allocated, then the replacement of a page in memory is required at the request of a new page. This is referred to as demand-paging.
• The choice of which page to replace is specified by a page replacement algorithm. The commonly used page replacement algorithms are FIFO, LRU, optimal page replacement algorithms, etc.
• Generally, on increasing the number of frames to a process’s virtual memory, its execution becomes faster as less number of page faults occur. Sometimes the reverse happens, that is, more numbers of page faults occur when more frames are allocated to a process. This most unexpected result is termed as Belady’s Anomaly.
• FIFO and random replacement algorithms suffer from Belady’s Anomaly.