A
concept found in page swapping
algorithms. When using a
first-in-first-out method of page swapping, if you increase the number of
frames, it is possible that it will increase the number of
page faults. This is contrary to the intent of adding more frames, thus the
anomaly. This is one reason why a FIFO approach is not recommended.
As an example, take the following list of page references: 123412512345212345.
Here are the frame
contents with three frames
*:
123412555344211345
12341222533422134
1234111255344213
Now here are the contents with four frames:
123444512345512345
12333451234451234
1222345123345123
111234512234512
So there are fourteen page faults with three frames, but fifteen with four frames. This does not happen with the
least-recently-used approach.
**
*Emphasized frames represent page faults.
**Incidentally, the lru algorithm for this set of page references would result in 15 page faults with three frames and 12 page faults with four frames.