Using the IEFUSI installation exit to set process limits

The IEFUSI and IEALIMIT installation exits control region size and memory above the bar, but z/OS UNIX ignores changes made by IEALIMIT. Changes made by IEFUSI to the region limit and hi memory limit are used if a RACF® user profile is not used to define these values for the user. The IEFUSI exit can change the values used by the system for virtual storage available above and below the 16M line, and hi memory. Normally, z/OS UNIX takes action to ensure that these changes are honored. When a limit is specifically defined for a user via the OMVS segment, z/OS UNIX will ignore the changes made by the IEFUSI exit if the ASSIZE or MEMLIMIT in the OMVS segment is specified as a higher value than IEFUSI.

Because z/OS UNIX limits are normally inherited from MVS™, the IEFUSI exit has already had a chance to modify the region size and MEMLIMIT for TSO, batch, and started task. The exit does not have to be called again during OMVS subsystem processing. z/OS UNIX processes such as telnet and rlogin do not have a chance to change the limits, so IEFUSI is not needed to control those limits.

Rule: If you install your own IEFUSI exit, update your SMFPRMxx parmlib member to exclude OMVS work and use z/OS UNIX to control the process limit. Specify:

SUBSYS(OMVS,NOEXITS)

Started subtasks such as OMVS, BPXOINIT, and colony address spaces fall under SUBSYS STC. These address spaces might be subject to IEFUSI limitations if IEFUSI exits are allowed for SUBSYS STC. IBM® strongly recommends that you always set REGION=0 and MEMLIMIT=NOLIMIT for OMVS, BPXOINIT, and colony address spaces.

Message IEE968I is issued when the SET SMF= command is processed because z/OS UNIX does not support the SSI Notify function. You can ignore this message.

After a hard limit is defined in the user RACF profile, the parents' hard and soft values for that limit will override IEFUSI, MVS, and z/OS UNIX changes in any child processes or executed programs. An executed or spawned process after an identity change always set hard and soft limits to the OMVS limit of the new identity. Other processes exhibit this behavior only if the value in the user RACF profile was higher than the value provided by MVS when the process was dubbed.

For more information about the IEFUSI installation exit, see Using the IEFUSI step initiation exit and z/OS MVS Installation Exits.