I still don't really understand the problem/concern,
but hopefully this answers any questions remaining.

As the documentation describes, there are roughly 2050 pages of
non-pageable structures for 1GB of vdisk space. On older releases,
z/VM 5.3, these structures were restricted below 2GB.  The first
check is to ensure these will not consume more that 1/4 of DPA.
For current releases, I believe the easiest approximation of this
is to take all the frames above 2GB add the Pageable Frames below
2GB (see QUERY FRAMES), subtract RealFreeStorage, LockedRS,
Nucleus/Prefix, Trace, Other (also from QUERY FRAMES).
As the documentation describes, take 25% of that and divide by
2050. This gives the DPA bounded limit in GBs of vdisk space.

For the paging space, it is just like the documentation describes.
The easiest approach is do a QUERY ALLOC PAGE. Take the sum
of the page slots (not counting any Drained or Draining volumes.)
Take 25% of this value divide by 262144 (page slots in a GB) to
get the page space bounded limit.

Use the minimum of those two values.

Perhaps I am too close to the subject to judge the clarity
of the documentation. If you feel there is need for
improvement, reader's comments can be submitted on the web:
http://www-03.ibm.com/systems/z/os/zvm/zvmforms/webqs.html

Regards,
Bill

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