Thrashing

• If the number of frames allocated to a low-priority process falls below the minimum number required, we must suspend that process's execution. We should then page out its remaining pages, freeing all its allocated frames.
• In fact, look at any process that does not have ``enough'' frames.
  • If the process does not have the number of frames it needs to support pages in active use, it will quickly page-fault.
  • At this point, it must replace some page.
  • However, since all its pages are in active use, it must replace a page that will be needed again right away.
  • Consequently, it quickly faults again, and again, and again, replacing pages that it must bring back in immediately.
• This high paging activity is called thrashing. A process is thrashing if it is spending more time paging than executing.