<?xml version="1.0" encoding="utf-8"?>

<!-- Copyright (c) 2007-2010 Nokia Corporation and/or its subsidiary(-ies) All rights reserved. -->

<!-- This component and the accompanying materials are made available under the terms of the License 

"Eclipse Public License v1.0" which accompanies this distribution, 

and is available at the URL "http://www.eclipse.org/legal/epl-v10.html". -->

<!-- Initial Contributors:

    Nokia Corporation - initial contribution.

Contributors: 

-->

<!DOCTYPE concept

  PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

<concept id="GUID-95840076-79F2-524B-BAF7-828260BDD923" xml:lang="en"><title>Patchable

Constants: KHeapShrinkHysRatio</title><prolog><metadata><keywords/></metadata></prolog><conbody>

<codeblock id="GUID-5053B8C4-B730-5341-98A3-801409460573" xml:space="preserve">EXPORT_C extern const TInt KHeapShrinkHysRatio;</codeblock>

<table id="GUID-EA923219-CBC1-5F40-9EF3-30EE85C02F76">

<tgroup cols="2"><colspec colname="col0"/><colspec colname="col1"/>

<tbody>

<row>

<entry><p>Exported from: </p> </entry>

<entry><p> <filepath>EUSER.DLL</filepath>, <filepath>EKERN.EXE</filepath>  </p> </entry>

</row>

<row>

<entry><p>Defined in: </p> </entry>

<entry><p> <filepath> .../os/kernelhwsrv/kernel/eka/common/heap.cpp</filepath>  </p> </entry>

</row>

<row>

<entry><p>Purpose: </p> </entry>

<entry><p>This constant defines the ratio that determines the amount of hysteresis

between heap growing and heap shrinking. It is a 32-bit fixed point number

where the radix point is defined to be between bits 7 and 8 (where the LSB

is bit 0) i.e. using standard notation, a Q8 or a fx24.8 fixed point number.

For example for a ratio of 2.0 set <codeph>KHeapShrinkHysRatio=0x200</codeph>. </p> <p>The

heap shrinking hysteresis value is calculated to be: </p> <codeblock id="GUID-1144F94A-6B4C-582D-B1FA-E5852F6BFAA6" xml:space="preserve">KHeapShrinkHysRatio*(iGrowBy&gt;&gt;8)</codeblock> <p>where <codeph>iGrowBy</codeph> is a page aligned value set by the argument, <codeph>aGrowBy</codeph>,

to the <xref href="GUID-EFAFDD75-7E59-306A-882D-317F5564979E.dita"><apiname>RHeap</apiname></xref> constructor. Default hysteresis value is <codeph>iGrowBy</codeph> bytes

i.e. <codeph>KHeapShrinkHysRatio=2.0</codeph>. Memory usage may be improved

by reducing the heap shrinking hysteresis by setting 1.0 &lt; <codeph>KHeapShrinkHysRatio</codeph> &lt;

2.0. Heap shrinking hysteresis is disabled/removed when <codeph>KHeapShrinkHysRatio</codeph> &lt;=

1.0. </p> </entry>

</row>

</tbody>

</tgroup>