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Adaptation/GUID-44540C74-CD73-5D8E-A9E0-F90F46B4E7B1.dita
author Graeme Price <GRAEME.PRICE@NOKIA.COM>
Fri, 15 Oct 2010 14:32:18 +0100
changeset 15 307f4279f433
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<?xml version="1.0" encoding="utf-8"?>
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<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->
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<!-- This component and the accompanying materials are made available under the terms of the License
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"Eclipse Public License v1.0" which accompanies this distribution,
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and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->
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<!-- Initial Contributors:
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    Nokia Corporation - initial contribution.
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Contributors:
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-->
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<!DOCTYPE concept
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  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">
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<concept id="GUID-44540C74-CD73-5D8E-A9E0-F90F46B4E7B1" xml:lang="en"><title>Preventing
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And Recovering From Thrashing Tutorial</title><shortdesc>Describes how to reduce the chance of thrashing occurring in demand
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memory and how to recover from thrashing. </shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>
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<section id="GUID-B9C385CD-A155-52F9-9001-C219A9AD52DB"><title>Introduction</title> <p>Thrashing
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is a state where the vast majority of the processing time is spent paging
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memory in and out of the system and very little is spent useful work. If this
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situation persists, then the system performance rapidly becomes unacceptable
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and will appear to the user to have hung. </p> </section>
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<section id="GUID-D93027E5-EC83-431B-872C-17F81F5FD64B"><title>Background information</title><p>The following is useful background
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reading: </p><ul>
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<li><p> Thrashing </p></li>
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</ul> </section>
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<section id="GUID-6EAA97DD-B352-4C40-9A41-4F60F2A34A8B"><title>Thrashing features</title><p>When thrashing occurs the device
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will appear to do nothing or 'hang' for  period. Unlike a deadlock however,
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the device can recover from thrashing.</p> </section>
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<section id="GUID-6355035F-BBE3-4D33-8B02-76BA7B40AA0B"><title>Prevention of thrashing</title><p>The following can be used
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reduce the chance of thrashing: </p><ul>
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<li><p>Compress pages in memory to decrease the amount of memory that has
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to  be paged in and out </p></li>
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<li><p>Limit the maximum size of each process's paged memory to the minimum
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size of the paging cache </p></li>
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<li><p>Partition the page cache per-process and allocate pages to processes
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 based on the Working Set Size (WSS) of threads in that process</p></li>
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<li><p>Swap out the oldest pages in advance to free up memory to cope with
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spikes in paging demand</p></li>
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<li><p>Don't let threads steal pages from other threads </p></li>
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</ul> </section>
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<section id="GUID-5E119B58-E5C5-49AD-95B3-76DDDD4AF0CD"><title>Recovery from thrashing</title> <p>The possible courses of
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action to undertake, should thrashing occur, are : </p> <ul>
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<li id="GUID-50BE3032-DE49-575A-B2A8-20D12F387C86"><p>Reboot the device </p> </li>
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<li id="GUID-DFB20955-70DA-5403-BFDD-D45B50926E98"><p>Kill a thread </p> </li>
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<li id="GUID-DF970B70-A9BA-5532-A267-5920950F6F2A"><p>Decrease the number
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of paged threads running concurrently </p> </li>
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<li id="GUID-B849006B-66E7-5F31-8225-297235614AC4"><p>Pick one thread with
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a high page fault rate and stop other threads stealing pages from the thread's
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associated process </p> </li>
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<li id="GUID-0497BC30-7BCA-5E69-A835-722C80EA2680"><p>Prompt the user-side
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memory manager to close down applications. </p> </li>
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</ul> </section>
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</conbody><related-links>
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<link href="GUID-ACB79CEF-CA4D-5C96-AFCD-6AD7C7C26C53.dita"><linktext>Thrashing
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guide</linktext></link>
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</related-links></concept>
MCL/sftools/depl/docscontent