The FastLoad Facility

The FastLoad Facility is an MSO feature which greatly reduces the time required to load program modules into storage.

Using the FastLoad facility enables faster logons, allowing applications to start more quickly, and reducing storage fragmentation in the MSO address space.

FastLoad works by pre-fetching a copy of a module and saving it, along with relocation information, in the MSO address space. When the module needs to be loaded, FastLoad makes an in-storage copy, thus bypassing MVS program fetch, and eliminating the need to perform any I/O (other than paging I/O) to load the module. This reduction in I/O results in a substantial reduction in the elapsed time required to load a module.

FastLoad may be used with non-reentrant modules that normally load above the 16-megabyte line (i.e., they have an RMODE of ANY). Reentrant modules may also be FastLoaded. In this case, no copy is made, but the initial copy is kept in storage for all other users, thus reducing storage fragmentation. FastLoad may not be used for modules that have RMODE 24.

FastLoad is enabled by specifying the FASTLOAD keyword in the MSO configuration file (see The MSO Configuration File). Each module to be FastLoaded requires a separate record in the file.

We recommend the use of FastLoad for modules that are over 200K and will be used by one or more MSO users. Consider FastLoading the following modules:

Reentrant modules should not be FastLoaded if they already reside in the XLPA. FSROOT is often installed into the XLPA during FOCUS installation. You should verify if this took place before using FastLoad with F$ROOT or other reentrant module.

Modules over 200K in size are good candidates for FastLoad. The benefits of using FastLoad on smaller modules are low, resulting in only minor savings. Never specify FOCDIR or FSASLIB because they will not work properly if FastLoaded.

When using FastLoad, preloading copies of FOCUS by specifying a high NUMBER_READY in the configuration file (see The MSO Configuration File) is not particularly necessary, since FastLoad can dynamically initialize a copy of FOCUS relatively quickly. However, by moving this work from a user's logon to the MSO region's startup, there is still some benefit available from specifying a NUMBER_READY equal to the anticipated user count. Both capabilities can be used together: copies of FOCUS loaded by NUMBER_READY do take advantage of FastLoad.

In addition, using the MVS LLA and VLF facilities on FOCLIB.LOAD is not as beneficial as it would be without the FastLoad Facility, although it will still result in a reduction of I/O to FOCLIB. This reduction will be more pronounced when multiple MSO address spaces are used, or when there is batch or TSO-based usage of FOCUS.