Web console shows less maximum memory as much is expected in JBoss EAP.

Solution Verified - Updated -

Environment

  • Red Hat JBoss Enterprise Application Platform (EAP)
    • 5.x
    • 6.x

Issue

  • Is it a bug that the web console show a different 'Max' value for the total Heap memory?
  • Why there is a difference between the heap size set by JVM option and the total Heap memory shown in JBoss web console?
  • Difference is shown in the maximum head memory shown in jconsole and the provided in conf file.

Resolution

  • This is not a JBoss issue as the 'Max' value for 'Heap usage' is provided by an JVM MBean and depend on the JVM implementation.

Root Cause

  • The values are provided by the JVM.
  • By default the Heap is split into Eden, Tenured (old) and two survivor spaces, see java gc tuning
  • The calculation of the JVM summarize only with one survivor space not both.
  • There comes the difference between the configured 'Max' value and the real memory consumption.

Diagnostic Steps

  • Set a fix memory allocation:
JAVA_OPTS="-Xms1304m -Xmx1304m -XX:MaxPermSize=256m ..."

compare the values between jconsole and JBoss web console.

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