IZ85288: GRADUAL MEMORY LEAK IN THE JAVA JIT DATA CACHE

APAR status

• Closed as program error.

Error description

• Error Message: When running applications with a high rate of
  class unloading (i.e. classes are loaded, used briefly or not at
  all, and then unloaded quickly), the Java 5 or Java 6 JVM may
  gradually increase the amount of memory it allocates for the JIT
  data cache without any apparent limit.
  The symptom can be observed by collecting a Java core dump from
  the JVM, by sending SIGQUIT (or Ctrl-Break on Windows) to the
  process. The dump lists all the JIT code cache segments and JIT
  data cache segments that have been allocated. If there are more
  memory segments in the JIT data cache than in the JIT code
  cache, the application may be suffering from the gradual memory
  leak. Eventually, the data cache could grow so large that all
  available memory is exhausted, and the JVM could crash due to a
  native out-of-memory condition.
  This problem is more pronounced on 64-bit platforms due to the
  larger pointer size.
  .
  Stack Trace: N/A
  .
  

Local fix

• This issue can be avoided if the application can be re-worked to
  reduce or eliminate class unloading. If that is not feasible,
  the memory leak can also be stopped by setting the environment
  variable TR_DisableCCR=1 before invoking the JVM. Note that this
  can cause the JIT compiler to compile fewer methods, reducing
  the overall performance of the application.
  

Problem summary

• The JIT data cache contains meta-data that describe JIT-compiled
  methods. Its size is usually a fraction of the size of the JIT
  code cache. For performance reasons, the maximum size of the JIT
  data cache is not hard-coded. The memory leak occurs when the
  JIT data cache is populated with an excessive amount of
  meta-data pertaining to classes that have been unloaded.
  

Problem conclusion

• This defect will be fixed in:
  6.0.0 SR9
  5.0.0 SR12 FP2
  .
  A new option has been added to Java 5 and Java 6 to allow users
  experiencing this issue to control the size of the JIT data
  cache. The option must be added to the JVM command line, and its
  syntax is:
  -Xjit:dataTotal=nnnn
  where "nnnn" is the maximum size of the data cache in kilobytes.
  For example, setting "nnnn" to 65536 limits the data cache to
  64MB. Note that the JIT compiler will be unable to compile more
  methods when the JIT data cache becomes full; to pick an optimal
  value for "nnnn", careful measurement and tuning is recommended.
  If the option is not used, the JVM assumes its original
  behaviour, i.e. the size of the JIT data cache is unlimited.
  .
  To obtain the fix:
  Install build 20100928 or later
  

Temporary fix

Comments

APAR Information

• APAR is sysrouted FROM one or more of the following:

  IZ85265

• APAR is sysrouted TO one or more of the following:

Fix information

• Fixed component name

  JAVA 5 JIT

• Fixed component ID

  620500124

Applicable component levels

• R500 PSN

     UP