Explain page replacement policies and concepts in os
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Prerequisite – Page Replacement Algorithms
In Operating System, process data is loaded in fixed sized chunks and each chunk is referred to as a page. The processor loads these pages in the fixed sized chunks of memory called frames. Typically the size of each page is always equal to the frame size.
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 replacement of a page in memory is required on 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 algorithms. The commonly used page replacement algorithms are FIFO, LRU, optimal page replacement algorithms etc.
Generally, on increasing the number of frames to a process’ virtual memory, its execution becomes faster as less number of page faults occur. Sometimes the reverse happens, i.e. more number of page faults occur when more frames are allocated to a process. This most unexpected result is termed as Belady’s Anomaly.
Bélády’s anomaly is the name given to the phenomenon where increasing the number of page frames results in an increase in the number of page faults for a given memory access pattern.
This phenomenon is commonly experienced in following page replacement algorithms:
In Operating System, process data is loaded in fixed sized chunks and each chunk is referred to as a page. The processor loads these pages in the fixed sized chunks of memory called frames. Typically the size of each page is always equal to the frame size.
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 replacement of a page in memory is required on 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 algorithms. The commonly used page replacement algorithms are FIFO, LRU, optimal page replacement algorithms etc.
Generally, on increasing the number of frames to a process’ virtual memory, its execution becomes faster as less number of page faults occur. Sometimes the reverse happens, i.e. more number of page faults occur when more frames are allocated to a process. This most unexpected result is termed as Belady’s Anomaly.
Bélády’s anomaly is the name given to the phenomenon where increasing the number of page frames results in an increase in the number of page faults for a given memory access pattern.
This phenomenon is commonly experienced in following page replacement algorithms:
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