Enabling 31-bit WebSphere Application Server on IBM System z to use 1 GB JVM

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A 31-bit WebSphere® Application Server on IBM® System z® must be changed to use a 1 GB Java™ Virtual Machine (JVM), in order to improve performance.

Normally, you cannot define more than 768 MB of JVM heap on a 31-bit distribution of WebSphere Application Server. However, with Linux®, you can use the mapped_base support to enable your system to have up to 1 GB of heap. Unpredictable results occur if you exceed the 1 GB value. To enable this capability, place this line into the startServer.sh startup script:

echo 268435456 >/proc/self/mapped_base

The startServer.sh script now looks like this (bold is added for emphasis only):

nwas3:/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/bin # cat startServer.sh
#!/bin/sh
echo 268435456 >/proc/self/mapped_base
WAS_USER_SCRIPT=/opt/IBM/WebSphere/AppServer/profiles/AppSrv01/bin/setupCmdLine.sh
export WAS_USER_SCRIPT
/opt/IBM/WebSphere/AppServer/bin/startServer.sh "$@"