Os Memory Management Questions Medium
The LRU-K (Least Recently Used K) page replacement algorithm is an enhancement of the traditional LRU (Least Recently Used) algorithm. It aims to improve the accuracy of page replacement decisions by considering the recent history of page accesses.
In the LRU-K algorithm, each page in memory is associated with a counter that keeps track of the number of references made to that page. When a page needs to be replaced, the algorithm selects the page with the lowest counter value as the least recently used page.
The key difference in the LRU-K algorithm is the introduction of the parameter K, which represents the number of most recent references to consider when making replacement decisions. This means that the algorithm takes into account not only the immediate past but also the recent history of page accesses.
Here is a step-by-step description of how the LRU-K algorithm works:
1. Initialize the counters for all pages in memory to 0.
2. When a page is accessed, increment its counter value by 1.
3. When a page needs to be replaced:
a. Select the page with the lowest counter value as the least recently used page.
b. If there are multiple pages with the same lowest counter value, choose the one that was referenced least recently among them.
4. After replacing a page, update the counters for all pages in memory:
a. Decrement the counter value of the replaced page by 1.
b. For all other pages, shift their counter values to the right by 1.
c. Set the counter value of the newly brought-in page to K (indicating it was recently referenced).
5. Repeat steps 2-4 for subsequent page accesses and replacements.
By considering the recent history of page accesses, the LRU-K algorithm can better adapt to the changing access patterns of a system. The value of K determines the level of accuracy in predicting future page accesses. A higher value of K provides a longer history and may result in better performance, but it also requires more memory overhead to store the counters.