PH38125: CICS SOS for 64 bit memory when substantial guarded storage is used.

Obtain the fix for this APAR.

APAR status

• Closed as program error.

Error description

• A customer saw message:
  
  DFHSM0606 The amount of MVS above the bar storage available to
  CICS is critically low
  
  Dump analysis showed this is due to large amounts of 64 bit
  memory which is guarded.
  
  Hidden or guarded memory is a memory range that is set aside by
  RSM for use by a memory allocator, when the allocating caller
  indicates this using the GUARDSIZE() parameter on an
  IARV64 REQUEST(GETSTOR) ...
  macro call. These areas are not currently allocated and do not
  represent a resource that is in use, but rather a potential use
  at some unknown point in the future.
  
  In the customer case the usage was driven by a high number of
  pthreads in a region with multiple JVM servers. Each pthread
  has 16MB of guarded storage, since LE specifies this
  GUARDSIZE in response to the LE STACK64 runtime option max
  value, which is set to 16MB via the CICS supplied module
  DFHAXRO by default for CICS JVM server resources.
  
  CICS issues message DFHSM0606 and fails or waits callers that
  need 64 bit memory because its calculation compares a value
  for allocated memory including both committed and guarded
  storage against the current MEMLIMIT value.
  
  This forces the customer to circumvent the SOS via a config
  change, for example:
  - estimating an increased MEMLIMIT that takes into account
  likely guarded memory usage
  - reducing the LE STACK64 max value
  - reducing the number of pthreads in use.
  
  
  
  Additional keywords / symptoms:
  DFHSM0143
  

Local fix

Problem summary

• ****************************************************************
  * USERS AFFECTED: All CICS Users.                              *
  ****************************************************************
  * PROBLEM DESCRIPTION: Message DFHSM0606 can be issued when    *
  *                      additional storage is available within  *
  *                      the current MEMLIMIT.                   *
  ****************************************************************
  When determining if a further extent of 64 bit private storage
  would be obtainable, CICS takes into account storage that is
  marked as guarded to the MVS RSM component.
  
  In some environments where there is a substantial use of guarded
  storage, CICS can issue message DFHSM0606 when an RSM call to
  obtain memory for the further extent would succeed. This is
  because RSM does not factor in guarded memory against the
  current MEMLIMIT value.
  

Problem conclusion

• CICS no longer factors in guarded storage when determining
  if an additional extent of 64 bit memory can be obtained.
  
  Following this change, message DFHSM0606 will be
  issued when no further extent can be allocated within the
  current MEMLIMIT.
  

Temporary fix

Comments

APAR Information

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

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

  UI77772 UI77773

Modules/Macros

• DFHS2PP  DFHS2SQ  DFHSMSY
  

Fix information

• Fixed component name

  CICS TS Z/OS V5

• Fixed component ID

  5655Y0400

Applicable component levels

• R200 PSY UI77773

     UP21/10/23 P F110

• R300 PSY UI77772

     UP21/10/23 P F110

Fix is available

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