• If a process does not have “enough” pages, the page-fault rate is very high
– low CPU utilization
– OS thinks it needs increased multiprogramming
– adds another process to system
• Thrashing is when a process is busy swapping pages in and out.
• Thrashing results in severe performance problems. Consider the following scenario, which is based on the actual behaviour of early paging systems. The operating system monitors CPU utilization. If CPU utilization is too low, we increase the degree of multiprogramming by introducing a new process to the system. A global page replacement algorithm is used; it replaces pages with no regard to the process to which they belong. Now suppose that a process enters a new phase in its execution and needs more frames.