Os Memory Management Questions Medium
The LRU-K-4 (Least Recently Used with K and 4th Chance) page replacement algorithm is an enhancement of the traditional LRU (Least Recently Used) algorithm. It aims to improve the efficiency of page replacement by considering both the recency and frequency of page accesses.
In the LRU-K-4 algorithm, each page in memory is associated with a counter that keeps track of the number of times the page has been accessed. When a page fault occurs, the algorithm selects the page with the lowest counter value as the victim for replacement.
The algorithm also maintains a stack of recently accessed pages, ordered from most recently used to least recently used. This stack is used to determine the recency of page accesses. When a page is accessed, it is moved to the top of the stack, indicating that it is the most recently used page.
Additionally, the LRU-K-4 algorithm introduces the concept of the 4th chance. When a page is selected as a victim for replacement, it is given a 4th chance before being evicted from memory. During this 4th chance, if the page is accessed again, its counter value is incremented, and it is moved to the top of the stack. This allows frequently accessed pages to have a higher chance of remaining in memory.
The value of K in LRU-K-4 represents the number of times a page must be accessed before it is considered a candidate for replacement. If a page's counter value is less than K, it is not considered for replacement, regardless of its recency. This helps to prioritize pages that are accessed more frequently.
Overall, the LRU-K-4 algorithm combines the concepts of recency and frequency to make more informed decisions about page replacement. By considering both factors, it aims to improve the hit rate and reduce the number of page faults in memory management.