Thrashing +Guide

Introduction

Thrashing +is an undesirable state where most of the processes in the system are in the +process of paging-in memory and none of the threads are doing useful work. +This results in unacceptable system performance.

Background information

These topics are useful background +information on thrashing:

Paging
Virtual memory

Thrashing features

The signs of thrashing in demand +paging are:

The system performance rapidly becomes unacceptable, since no threads +are doing useful work. The device will become unresponsive or appear to 'hang'.
When observing paging activity logs it's seen that the same set of +pages are paged in and out many times over the course of a use case.
When observing paging activity logs there are long periods where many +threads are waiting for pages to be paged in.
There are large periods of null thread activity.

Thrashing prevention

The following is a means of +preventing thrashing from occurring:

Increase the size of the paging cache. This reduces page faults and +hence the need to page-in memory.
Mark the code or data involved as unpaged, for example if a 20MB buffer +is actively used through a use-case and discarded afterwards there is little +use in making it paged as it will need to always be in the page cache.
Reduce the working set size so that it fits into the paging cache, +for example instead of having four activities running concurrently, serialize +them.