Specifying region size

Users can specify a job's region size by coding the REGION parameter on the JOB or EXEC statement. The system rounds all region sizes to a 4K multiple.

The region size value should be less than the region limit value to protect against programs that issue variable length GETMAINs with very large maximums, and then do not immediately free part of that space or free such a small amount that a later GETMAIN (possibly issued by a system service) causes the job to fail.

For V=V jobs, the region size can be as large as the entire private area, minus the size of LSQA/SWA/user key area (subpools 229, 230, and 249) and the system region (see Figure 1).

For V=R jobs, the REGION parameter value cannot be greater than the value of the REAL system parameter specified at IPL. If the user does not explicitly specify a V=R job's region size in the job's JCL, the system uses the VRREGN system parameter value in the IEASYS00 member of SYS1.PARMLIB.

For more information on coding the REGION parameter, see z/OS MVS JCL Reference.

Note: VRREGN should not be confused with the REAL system parameter. REAL specifies the total amount of central storage that is to be reserved for running all active V=R regions. VRREGN specifies the default subset of that total space that is required for an individual job that does not have a region size specified in its JCL.

An installation can override the VRREGN default value in IEASYS00 by:

Using an alternate system parameter list (IEASYSxx) that contains the desired VRREGN parameter value.
Specifying the desired VRREGN value at the operator's console during system initialization. This value overrides the value for VRREGN that was specified in IEASYS00 or IEASYSxx.

For V=R requests, if contiguous storage of at least the size of the REGION parameter or the system default is not available in virtual or central storage, a request for a V=R region is placed on a wait queue until space becomes available.

Note that V=R regions must be mapped one for one into central storage. Therefore, they do not have their entire virtual storage private area at their disposal; they can use only that portion of their private area having addresses that correspond to the contiguous central storage area assigned to their region, and to LSQA, SWA, and subpools 229, 230, and 249.