Limitations for 64-bit addressing

Keyword MEMLIMIT in SYS1.PARMLIB(SMFPRMxx) limits how much virtual storage a 64-bit task can allocate above the 2GB bar. Unlike the REGION parameter in JCL, MEMLIMIT=0M means that the process cannot use virtual storage above the bar.

If MEMLIMIT is not specified in SMFPRMxx, the default value is 2G, allowing 64-bit tasks to use up to 4GB (the 2GB below the bar and the 2GB above the bar granted by MEMLIMIT).

SYS1.PARMLIB(SMFPRMxx) values can be checked and activated with the following console commands, as described in MVS System Commands (GC28-1781):
  1. DISPLAY SMF,O
  2. SET SMF=xx

MEMLIMIT can also be specified as parameter on an EXEC card in JCL. If no MEMLIMIT parameter is specified, the default is the value defined to SMF, except when REGION=0M is specified, in which case the default is NOLIMIT.