Access time for modules

From a performance standpoint, modules not already loaded in an address space will usually be available to a program in the least time when found at the beginning of the following list, and will take more time to be available when found later in the list. Remember that the system stops searching for a module once it has been found in the search order; so, if it is present in more than one place, only the first copy found will be used. The placement of the first copy in the search order will affect how long it takes the system to make the module available. Possible places are:

LPA
Link list concatenation (all directory entries and some modules cached automatically)
TASKLIB/STEPLIB/JOBLIB (with LLA caching of the library)
TASKLIB/STEPLIB/JOBLIB (without LLA caching of the library).

For best application performance, you should place as many frequently-used modules as high on this list as you can. However, the following system-wide factors must be considered when you decide how many load modules to place in LPA:

Performance
When central storage is not constrained, frequently-used LPA routines almost always reside in central storage, and access to these modules will be very fast.
Virtual Storage
How much virtual storage is available for address spaces that use the modules placed in LPA, and how much is available for address spaces that do not use the modules placed in LPA.