MIM support of REUSASID for reusing an address space

Document ID : KB000050875
Last Modified Date : 14/02/2018
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A z/OS address space is assigned an ASID when it is created. Address spaces such as MIM that use cross memory services can produce a lost ASID upon termination if the cross memory services are not properly coded for address space reuse.


During initialization, MIM uses IBM-documented interfaces to establish a cross memory environment. The MIM cross memory services are coded in a manner which allows MIM to reuse the address space across MIM restarts that occur within the lifetime of the IPL. If MIM terminates and is restarted without performing an IPL, MIM can be assigned a reusable address space, but only if MIM is started each time by specifying the z/OS parameter REUSASID=YES on the z/OS START command. Here is an example of starting MIM with the REUSASID option:


Although REUSASID is a z/OS parameter, it can also be used when overriding select MIM startup parameters on the START command, as shown in this example:


REUSASID=YES is useful in avoiding a situation where an address space creation fails with message:


REUSASID=YES is also useful in avoiding situations where address space termination results in the following message which indicates a potentially lost ASID:


MIM customers typically do not restart MIM multiple times during the lifetime of a system IPL in a production environment. However, in situations where MIM might be started multiple times, such as a test environment, MIM is capable of reusing an ASID and will do so if started with REUSAID=YES. Therefore, MIM will not contribute to a situation in which the available ASIDs are exhausted, a situation which may require a system IPL to resolve.

Some customers use the MIM address space creation utility to start MIM as a system address space. When MIM invokes the ASCRE macro, it hardcodes the REUSASID attribute, making the address space available for reuse when MIM terminates. Therefore, customers who use the MIM address space creation utility need to take no action in order for MIM to be assigned a reusable address space.

Reference the IBM Extended Addressability Guide for more information on reusing ASIDs when coding cross memory services. Reference the IBM MVS System Commands manual for more information on the z/OS START command and its REUSASID option.