Suppose that the virtual page reference stream contains repetitions of long sequ

Question

Suppose that the virtual page reference stream contains repetitions of long sequences of page references followed occasionally by a random page reference. For example, the sequence: 0, 1, ... , 511, 431, 0, 1, ... , 511, 332, 0, 1, ... consists of repetitions of the sequence 0, 1, ... , 511 followed by a random reference to pages 431 and 332. (a) Why will the standard replacement algorithms (LRU, FIFO, clock) not be effective in handling this workload for a page allocation that is less than the sequence length? (b) If this program were allocated 500 page frames, describe a page replacement approach that would perform much better than the LRU, FIFO, or clock algorithms.

Explanation / Answer

( 1 – Hit Ratio(when the item being searched is found out in the cache) )

* Time needed to access the main memory

+ Time for latency (time gap between request and response)

+ Time for the secondary effects

(a) The LRU, FIFO and CLOCK are standard or conservative algorithms and are

not effective in handling this workload for a page allocation that is

less than the sequence length for the following reasons:

(b) algorithms better than LRU, FIFO and CLOCK:

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