6. DATA SOURCES › 6.4 Expanded Storage Concepts › 6.4.5 Users of Expanded Storage

6.4.5 Users of Expanded Storage

Unauthorized programs cannot directly allocate or manipulate
expanded storage.  Rather, expanded storage is used as a
system control program resource and controlled by the RSM to
maximize responsiveness and throughput of the system.

The RSM categorizes expanded storage use by the type of
paging group and by the status of the page being considered
for placement in expanded storage.  The paging group can be
a:

    Type 0 - Privileged or non-swappable (including all
             common areas) address space,

    Type 1 - Any other type of page not included in types 0
             or 2, or

    Type 2 - A page belonging to a TSO user waiting for
             terminal I/O to complete, or pages paged-out or
             stolen from a TSO user.

The page's status is categorized as a:

    Changed paged-out page
    Changed swapped-out page
    Changed stolen page
    Unchanged paged-out page
    Unchanged swapped-out page
    Unchanged stolen page
    Working set page ready for swap-out
    Virtual fetch page
    VIO swapped-out page
    Hiperspace page

Different criteria ages can be specified for each combination
of paging type and page status with the exceptions of virtual
fetch, VIO, and hiperspace pages.  These last three
categories have a single criteria age specification without
paging type classification differences.  This allows the
installation to tailor the configuration so that expanded
storage usage is prioritized by the type of address spaces
that are most important in the specific processor complex.
Indeed, it is possible to set the parameters so that some of
the combinations are eligible and others ineligible to use
expanded storage.