Freeing of virtual storage

The system establishes two responsibility counts for every load module brought into virtual storage in response to your requests for that load module. The responsibility counts are lowered as follows:

If the load module was requested in a LOAD macro, that responsibility count is lowered when using a DELETE macro.
If the load module was requested on LINK, LINKX, ATTACH, ATTACHX, XCTL, or XCTLX, that responsibility count is lowered when using XCTL or XCTLX or by returning control to the system.
When a task is terminated, the responsibility counts are lowered by the number of requests for the load module made by LINK, LINKX, LOAD, ATTACH, ATTACHX, XCTL, or XCTLX during the performance of that task, minus the number of deletions indicated above.

The virtual storage area occupied by a load module is released when the responsibility counts reach zero. When you plan your program, you can design the load modules to give you the best trade-off between execution time and efficient paging. If you use a load module many times in the course of a job step, issue a LOAD macro to bring it into virtual storage; do not issue a DELETE macro until the load module is no longer needed. Conversely, if a load module is used only once during the job step, or if its uses are widely separated, issue LINK or LINKX to obtain the module and issue an XCTL or XCTLX from the module (or return control to the system) after it has been executed.

There is a minor problem involved in the deletion of load modules containing data control blocks (DCBs). An OPEN macro instruction must be issued before the DCB is used, and a CLOSE macro issued when it is no longer needed. If you do not issue a CLOSE macro for the DCB, the system issues one for you when the task is terminated. However, if the load module containing the DCB has been removed from virtual storage, the attempt to issue the CLOSE macro causes abnormal termination of the task. You must either issue the CLOSE macro yourself before deleting the load module, or ensure that the data control block is still in virtual storage when the task is terminated (possibly by issuing a GETMAIN and creating the DCB in the area that had been allocated by the GETMAIN).