Lecture 4

Question 1

Thrashing

Answer 1

occurs when processes does not have enough

assigned memory page frames and the page fault rate is very high.

Question 2

What can thrashing result in?

Answer 2

Low CPU utilization
OS spends most of its time swapping pages in and
out between main and secondary storage.

Question 3

What can happen if the degree of multi-programming is too much?

Answer 3

causing uncontrollable

thrashing, and eventual crashing of all process execution (i.e. zero CP U utilisation).

Question 4

When does thrashing occur?

Answer 4

High page fault rate, OS spends most its time handling page faults.
Specifically, thrashing is caused by a lack of main memory

Question 5

How to prevent thrashing?

Answer 5

use local or priority page replacement

Dynamic memory allocation and load-balancing methods such as working sets.

Question 6

Working set

Answer 6

Some minimum amount of pages needed for a process to behave well.

Question 7

Sequential locality

Answer 7

a special case of spatial locality that occurs when relevant data elements are arranged and accessed linearly

Question 8

Equidistant locality

Answer 8

a more general case that occurs when the linear traversal is over a longer area of adjacent data structures with identical structure and size,
accessing mutually corresponding elements of each structure rather than each entire structure