IEAPAKxx is an installation-supplied member that contains groups of names of modules in the LPALST concatenation that are executed together or in sequence. (As an example, the load modules of a type-4 SVC routine are called sequentially and executed as a group.) The member is used only during a “cold” start (CLPA specified), when the PLPA is loaded from the LPALST concatenation.
The system uses the specified IEAPAKxx member(s) to determine the order in which modules are to be loaded from the LPALST concatenation into the pageable LPA. These modules are packed together, if possible, on a single page. The purpose is to reduce page faults. The LPA can greatly contribute to page faults because it is highly used. The IEAPAKxx list can significantly reduce page faults.
Each group ideally should not exceed 4K bytes in size. If a group exceeds 4K, the module in the group that causes 4K to be exceeded, and all later modules in the same group, will be loaded at the next page boundary in the LPA. In contrast, the system loads other modules (those not listed in IEAPAKxx) in size order, the largest modules first, then the smaller modules. Unused spaces within page boundaries are filled, if possible, with modules smaller than 4K.
You should select link pack area programs for inclusion in the system pack list to reduce the number of page faults from the pageable link pack area and thereby enhance system performance. The affinity of programs for each other and the size of the programs determine which should be selected for a pack list entry. Program affinity means that one program will usually refer to another program when the first program is invoked. By putting programs that refer to each other into the same pack list entry, and thereby on the same page, extra page faults are avoided, because the programs are always in storage together.
Very large programs that are to be put into the link pack area should be link edited so that CSECTs that have affinity or other CSECTs are placed within the same page. The linkedit ORDER statement can be used to group CSECTs into pages. This process will accomplish the same goal as the pack list entries, because page faults during execution will be reduced. The modules either execute concurrently or call each other.