Monitoring CSM storage

System operators can issue the DISPLAY CSM command to monitor CSM storage usage.

Rule: CSM messages always start with the message prefix IVT.

For a complete list of messages issued by CSM, see the z/OS Communications Server: SNA Messages.

The DISPLAY CSM command yields the following information:

Amount of storage allocated to each pool
Amount of storage allocated to each user of the pool
If OWNERID=ALL is specified, the cumulative storage allocated to each user across all pools
If OWNERID is not specified, the highest level of fixed storage obtained since the last DISPLAY CSM command was issued without the OWNERID parameter.
If OWNERID is not specified, the highest level of fixed storage obtained since the IPL.
If OWNERID is not specified, the highest level of ECSA obtained since the last DISPLAY CSM command was issued without the OWNERID parameter.
If OWNERID is not specified, the highest level of ECSA obtained since the IPL.
If OWNERID is not specified, the names of CSM data spaces.
The maximum amount of fixed and ECSA storage that can be allocated by CSM and current values of fixed and ECSA storage.

Use the DISPLAY CSM command to identify a user of the pool that is consuming inordinate amounts of storage. This can happen if an application fails to free buffers that it obtained from CSM. The report of storage allocated to a user is based on the value of the user's owner_ID parameter. This is the OWNERID operand on the DISPLAY CSM command. CSM uses the application's address space identifier (ASID) as the OWNERID.

In some cases, the sum of the total of the storage allocated to all users of a pool might be greater than the total amount of storage allocated to a pool. This is caused by multiple buffer owners, which is a result from the creation of shared instances using the IVTCSM REQUEST=ASSIGN_BUFFER macroinstruction. The OWNERID information indicates the amount of storage that the user must free to enable the storage to be returned to the buffer pool. Issue the MODIFY CSM command to increase or decrease CSM storage limits without requiring a re-IPL.

The CSM monitor function is available to monitor CSM buffers between many components of z/OS® Communications Server. IBM® Software Support uses this function to help diagnose CSM storage problems.

This function is controlled using the Modify CSM command with the MONITOR operand. Valid options are MONITOR=YES, MONITOR=NO and MONITOR=DYNAMIC. If you choose MONITOR=DYNAMIC, CSM buffer monitoring is dynamically activated and deactivated. CSM dynamically activates CSM buffer monitoring when CSM storage usage reaches 80% of defined limits of the fixed storage or ECSA storage. It dynamically deactivates CSM buffer monitoring when CSM storage usage returns to 75% of defined limits of the fixed storage and ECSA storage. Use the Display CSM command with the MONITOR operand to display the function status.

Use the DISPLAY CSMUSE command to evaluate the use of storage managed by CSM. Although this command is similar to the DISPLAY CSM command, it provides a lower level of detail for storage usage; therefore, this command is different than that of the DISPLAY CSM command. This command is primarily intended for IBM service. However, it can also be beneficial to the user. The display output provides detailed information about each CSM storage pool. The detailed information describes storage as it corresponds to an identifier, which is referred to as a monitor ID. Monitor IDs describe specific z/OS Communications Server components. When CSM storage is associated with (or isolated to) a specific monitor ID, then IBM service can correlate the monitor ID to a component (usage or function) of z/OS Communications Server. This information can be useful when evaluating how z/OS Communications Server is using system storage or to help diagnose storage growth. See the z/OS Communications Server: IP and SNA Codes for the complete description of monitor IDs. The critical level storage usage is 90% or higher of ECSA MAX or FIXED MAX values specified in CSM parmlib IVTPRM00. The normal level storage usage is 80% or below of ECSA MAX or FIXED MAX values.

CSM issues some messages when CSM storage limits are at a critical level or exceeded. In this case, the system operator can issue the MODIFY CSM command to increase the amount of fixed or ECSA storage available for CSM.

For more information about these CSM commands, see the z/OS Communications Server: SNA Operation.

Use the DISPLAY TRL command to isolate a storage problem to a specific device. For more information, see z/OS Communications Server: SNA Diagnosis Vol 1, Techniques and Procedures. For more detail on the DISPLAY TRL command, see the z/OS Communications Server: SNA Operation.

CSM storage information is also provided to the performance monitor interface (PMI). This information is equivalent to the information provided for the summary format of the DISPLAY CSM command. See the z/OS Communications Server: SNA Customization for more information.

Applications using the CSM API can also request information about the status of CSM storage by issuing the IVTCSM REQUEST=RESOURCE_STATS macroinstruction.