What's the difference between MEM_ARGS and USER_MEM_ARGS?

When starting up Oracle WebLogic Server, you might find the following entries in the logs:

...<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: CDC_JOINED_DOMAIN=na.intranet.msd> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: MODULES_DIR=/u01/app/oracle/middleware/modules> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: INPUTRC=/etc/inputrc> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: MEM_ARGS=-Xms32m -Xmx200m -XX:PermSize=128m -XX:MaxPermSize=256m> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: CDC_JOINED_DC=usadadc04.na.intranet.msd> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: HISTSIZE=1000> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: WLS1211_PATCH_LIBPATH=/u01/app/oracle/middleware/patch_wls1211/profiles/default/native> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: CDC_LOCALHOST=devhost> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: WEBLOGIC_EXTENSION_DIRS=/u01/app/oracle/middleware/patch_wls1211/profiles/default/sysext_manifest_classpath> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: PATH=/u01/app/oracle/middleware/wlserver_12.1/server/bin:/u01/app/oracle/middleware/modules/org.apache.ant_1.7.1/bin:/apps/weblogic/jdk1.7.0_40/jre/bin:/apps/weblogic/jdk1.7.0_40/bin:/apps/weblogic/jdk1.7.0_40/bin:/usr/kerberos/bin:/usr/share/centrifydc/bin:/usr/local/bin:/bin:/usr/bin:/var/cfengine/bin> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: DERBY_TOOLS=/u01/app/oracle/middleware/wlserver_12.1/common/derby/lib/derbytools.jar> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: PATCH_CLASSPATH=/u01/app/oracle/middleware/patch_wls1211/profiles/default/sys_manifest_classpath/weblogic_patch.jar> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: COHERENCE_HOME=> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: KDE_IS_PRELINKED=1> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: DOMAIN_HOME=/u01/app/oracle/middleware/user_projects/domains/soadomain> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: USER_MEM_ARGS=-Xms32m -Xmx200m -XX:MaxPermSize=350m> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: KDE_NO_IPV6=1> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: DA_SESSION_ID_AUTH=81d6fb70-adcd-4576-a835-739ce09e4498> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: FEATURES_DIR=/u01/app/oracle/middleware/modules/features>

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: CDC_JOINED_SITE=USAda> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: SSH_ASKPASS=/usr/libexec/openssh/gnome-ssh-askpass> 

<May 3, 2016 12:36:01 PM> <FINEST> <NodeManager> <Environment: JAVA_VENDOR=Sun>...

Here, you notice 2 sets of memory settings; MEM_ARGS and USER_MEM_ARGS.

If the USER_MEM_ARGS environment variable is set, it overrides all MEM_ARGS values.