14 Thrashing

If process lacks frames it uses constantly, page-fault rate very high.

$\Rightarrow$ CPU-throughput decreases dramatically.
$\Rightarrow$ Disastrous effect on performance.

Two solutions

1. Working-set model (based on locality) :Define working set as set of pages used in the most recent $\Delta$ page references keep only working set in main memory.
   $\Rightarrow$ Achieves high CPU-utilisation and prevent thrashing.
2. Page-Fault Frequency : Takes direct approach.
   • Give process additional frames if page frequency rate high
   • Remove frame from process if page fault rate low.