- A machine has 24-bit byte-addressable virtual address space. The page size is
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Question
- A machine has 24-bit byte-addressable virtual address space. The page size is 2KB. How many pages of virtual address space exist?
- There is a program that causes a lot of “thrashing” every time it is run. A co-worker suggests I “change” the page replacement policy in my operating system to a FIFO algorithm instead of the LRU algorithm currently being used. Is my co-worker’s suggestion a good one? Why or why not? Knowing the data here, what general comments can be made about the program being run? Give an example of a program construct or property that could be causing the thrashing?
Explanation / Answer
No,the coworker suggetsion was not good as fifo has many disadvantages like Not always good at performance.
It may replace an active page to bring a new one and thus may cause a page fault of that page immediately.
To limit the effect of thrashing we can use local replacement algorithm. With Local replacement algorithm instead of fifo, if the process starts thrashing,
it cannot steal frames from another process and cause the latter to thrash as well. The problem is not entirely solved.
Thus the effective access time will increase even for the process that is not thrashing.
Knowing the data, we can say that CPU utilization was too low then there was increase in degree of multiprogramming by introducing a new process to the system.
The degree of multiprogramming was increased further, thrashing sets in and CPU utilization drops sharply.
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