The LRU Page Replacement Policy
In the Least Recently Used (LRU) page replacement policy, the page that is
used least recently
will be replaced.
Add a register to every page frame - contain the last time that the page in that frame was accessed
Use a "logical clock" that advance by 1 tick each time a memory reference is made.
Each time a page is referenced, update its register
The following figure shows the behavior of the program in paging using the LRU page replacement policy:
We can see notably that the
replacement decisions made by FIFO
is not present
There are a total of
9 page read operations
to satisfy the total of 18 page requests - that is almost a 20% improvement over FIFO in such a short experiment
(I only want to make the point here that page replacement policy can affect the system performance. I do not want to get into the question of "how much better is LRU than FIFO").
In fact, it has been shown empirically that LRU is the
preferred page replacement policy
Disadvantage of LRU replacement policy:
To identify the page to replace, you need to find the minimum time stamp value in all the registers...
Lots of work...
There is a more efficient scheme that
the behavior of LRU that runs more efficiently...
That method is "second chance" - next.