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Prerequisite – Least Recently Used (LRU) Page Replacement algorithm Least Recently Used page replacement algorithm replaces the page which is not used recently. Implementation: In this article, LRU is implemented using counters, a ctime (i.e., counter) variable is used to represent the current time, it is incremented for every page of the reference array. A vector of pair is used to represent the page frames, the 1’st variable of the pair is the page number and the second variable is the current time. When a new page is to be inserted and the frames are full, the page with minimum ctime is deleted (as it is the least recently used page). If the page is accessed again the value of ctime is updated. Note: Least ctime (counter / current time) value represents the least recently used page. Examples: Reference array is : 0, 0, 0, 2, 3, 0, 5, 7, 1, 2, 0, 8
Output :
When the number of frames is : 3
The number of page faults are : 9
Reference array is : 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 0, 1, 2, 3, 0, 0
Output :
When the number of frames is : 3
The number of page faults are : 15 Code: CPP#include using namespace std; // To calculate the number of page faultsvoid pageFaults(int frame_size, int* ref, int len, int ctime){ // Count variable to count the // number of page faults int cnt = 0; // Arr to simulate frames vector arr; // To initialise the array for (int i = 0; i < frame_size; i++) { arr.push_back(make_pair(-1, ctime)); } int page; for (int i = 0; i < len; i++) { page = ref[i]; auto it = arr.begin(); for (it = arr.begin(); it != arr.end(); it++) { if (it->first == page) { break; } } // If page is found if (it != arr.end()) { // update the value of // current time it->second = ctime; } // If page is not found else { // Find the page with min value of ctime, // as it will be the least recently used vector::iterator pos; pos = arr.begin(); int min = pos->second; for (auto itr = arr.begin(); itr != arr.end(); itr++) { if (itr->second < min) { pos = itr; min = pos->second; } } // Erase this page from the frame vector arr.erase(pos); // Insert the new page arr.push_back(make_pair(page, ctime)); cnt++; } ctime++; } cout |