LRU page replacement

In least lately used page replacement algorithm we will replace that page that hasn't been used for the longest period of time. This is similar as an optimal page replacement algorithm looking backward in time. It is considered as a good performer. 

There are two methods for execution that are counter and stack. Counter is the easiest to execute in which with each page entry there is a counter or logical clock. For every memory reference it is incremented. We reinstate the page with the smallest time value. In this overflow should be considered, in stack memory allocation when a page is referenced it is removed from the stack and put on top. For the reason that the entries may be in middle it is implemented using doubly linked list.

Example Consider the string 1,2,3,4,3,2,1. In this 1, 2, 3 are inserted as normal as 4 comes it is entered in the position of 1. When 1 comes again 4 is put back as it is the least referenced.