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<concept id="GUID-44540C74-CD73-5D8E-A9E0-F90F46B4E7B1-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1" xml:lang="en"><title>Preventing

And Recovering From Thrashing Tutorial</title><shortdesc>Describes how to reduce the chance of thrashing occurring in demand

memory and how to recover from thrashing. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

<section id="GUID-B9C385CD-A155-52F9-9001-C219A9AD52DB-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-1"><title>Introduction</title> <p>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. </p> </section>

<section id="GUID-D93027E5-EC83-431B-872C-17F81F5FD64B-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-2"><title>Background information</title><p>The following is useful background

reading: </p><ul>

<li><p> Thrashing </p></li>

</ul> </section>

<section id="GUID-6EAA97DD-B352-4C40-9A41-4F60F2A34A8B-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-3"><title>Thrashing features</title><p>When thrashing occurs the device

will appear to do nothing or 'hang' for  period. Unlike a deadlock however,

the device can recover from thrashing.</p> </section>

<section id="GUID-6355035F-BBE3-4D33-8B02-76BA7B40AA0B-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-4"><title>Prevention of thrashing</title><p>The following can be used

reduce the chance of thrashing: </p><ul>

<li><p>Compress pages in memory to decrease the amount of memory that has

to  be paged in and out </p></li>

<li><p>Limit the maximum size of each process's paged memory to the minimum

size of the paging cache </p></li>

<li><p>Partition the page cache per-process and allocate pages to processes

 based on the Working Set Size (WSS) of threads in that process</p></li>

<li><p>Swap out the oldest pages in advance to free up memory to cope with

spikes in paging demand</p></li>

<li><p>Don't let threads steal pages from other threads </p></li>

</ul> </section>

<section id="GUID-5E119B58-E5C5-49AD-95B3-76DDDD4AF0CD-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5"><title>Recovery from thrashing</title> <p>The possible courses of

action to undertake, should thrashing occur, are : </p> <ul>

<li id="GUID-50BE3032-DE49-575A-B2A8-20D12F387C86-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5-3-1"><p>Reboot the device </p> </li>

<li id="GUID-DFB20955-70DA-5403-BFDD-D45B50926E98-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5-3-2"><p>Kill a thread </p> </li>

<li id="GUID-DF970B70-A9BA-5532-A267-5920950F6F2A-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5-3-3"><p>Decrease the number

of paged threads running concurrently </p> </li>

<li id="GUID-B849006B-66E7-5F31-8225-297235614AC4-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5-3-4"><p>Pick one thread with

a high page fault rate and stop other threads stealing pages from the thread's

associated process </p> </li>

<li id="GUID-0497BC30-7BCA-5E69-A835-722C80EA2680-GENID-1-10-1-15-1-1-7-1-1-5-1-8-1-11-1-7-1-4-1-4-1-3-5-3-5"><p>Prompt the user-side

memory manager to close down applications. </p> </li>

</ul> </section>

</conbody><related-links>

<link href="GUID-ACB79CEF-CA4D-5C96-AFCD-6AD7C7C26C53.dita"><linktext>Thrashing

guide</linktext></link>

</related-links></concept>