Preventing +And Recovering From Thrashing Tutorial

Introduction

Thrashing +is a state where the vast majority of the processing time is spent paging +memory in and out of the system and very little is spent useful work. If this +situation persists, then the system performance rapidly becomes unacceptable +and will appear to the user to have hung.

Background information

The following is useful background +reading:

Thrashing

Thrashing features

When thrashing occurs the device +will appear to do nothing or 'hang' for period. Unlike a deadlock however, +the device can recover from thrashing.

Prevention of thrashing

The following can be used +reduce the chance of thrashing:

Compress pages in memory to decrease the amount of memory that has +to be paged in and out
Limit the maximum size of each process's paged memory to the minimum +size of the paging cache
Partition the page cache per-process and allocate pages to processes + based on the Working Set Size (WSS) of threads in that process
Swap out the oldest pages in advance to free up memory to cope with +spikes in paging demand
Don't let threads steal pages from other threads

Recovery from thrashing

The possible courses of +action to undertake, should thrashing occur, are :

Reboot the device
Kill a thread
Decrease the number +of paged threads running concurrently
Pick one thread with +a high page fault rate and stop other threads stealing pages from the thread's +associated process
Prompt the user-side +memory manager to close down applications.