Cannot allocate more than 1.5GB memory for JBoss EAP

Issue

• Need to increase heap size greater than 1.5GB for JDK based on application requirements
• JBoss runs really slow with currently allocated memory.
• When increased JDK memory using $JBOSS_HOME/jboss-as/bin/run.conf file's JAVA_OPTS, system complains that it does not have enough memory.
• Output of free -g shows that system has 10GB of memory available.
• We are trying to allocate more memory at JBoss server start up; we currently start server with 2048m as -Xms and 2048m as -Xmx. After some rounds of testing we found that we can start JBoss with 3072m but with 4096m server is not starting .