Description: Virtual storage requirements usually grow from release to release. You should review the virtual storage limits you want to set. Generally, there are two areas of concern: common areas (above and below the 16 MB line) and individual address spaces. An increase in virtual storage for common areas reduces the virtual storage size of all address spaces. An increase in virtual storage for individual address spaces impacts only the individual address spaces.
Element or feature: | Multiple. |
When change was introduced: | General migration action not tied to a specific release. |
Applies to migration from: | z/OS V1R13 and z/OS V1R12. |
Timing: | Before the first IPL of z/OS V2R1. |
Is the migration action required? | Yes. |
Target system hardware requirements: | None. |
Target system software requirements: | None. |
Other system (coexistence or fallback) requirements: | None. |
Restrictions: | None. |
System impacts: | None. |
Related IBM® Health Checker for z/OS® check: | Use IBM Health Checker for z/OS to help determine whether your virtual storage limits are set properly. The check RSM_MEMLIMIT checks the current setting for the MEMLIMIT parameter in SMFPRMxx, which affects the amount of virtual storage above the 2 GB bar that is available to jobs. This check verifies that a nonzero MEMLIMIT value is in use. |
Steps to take: Determine how much virtual storage use to allow above the 2 GB bar. While there is no practical limit to the number of virtual addresses an address space can request above the bar, the system can limit the amount of virtual storage above the bar that an address space is allowed to use. The amount of virtual storage above the bar is determined as follows. The MEMLIMIT parameter in parmlib member SMFPRMxx sets the default system-wide limit, which defaults to 2 GB as of z/OS V1R10 (and zero before z/OS V1R10). However, the system-wide default MEMLIMIT can be overridden by specifying REGION=0M or MEMLIMIT on JOB or EXEC statements in JCL. To set a limit on the use of virtual storage above the bar, use the SMF exit IEFUSI. For more information, see "Limiting the use of memory objects" in z/OS MVS Programming: Extended Addressability Guide.