Just a few days ago I saw a z/VSE 5.1 system, that did not use
the VTAM 31 bit I/O buffer support.
This support (available since z/VSE 3.1) allocates VTAM buffers
in 31 bit storage, which frees up some 24 bit space, that can
be used by your 24 bit (CICS) applications.
The 31 bit buffer support can be enabled, if you specifying
IOBUF31=YES in the VTAM startup book.
With z/VSE 4.3 we moved many data area, buffers and system routines
from 24 bit into 31 bit storage. You may see that relief if you
migrate to z/VSE 4.3 or z/VSE 5.1.
Some areas that could be sensitive to vendor program are only
moved into 31 bit storage, if you specify so via the IODEV
parameter in the IPL Supervisor parameters.
IODEV=1024: I/O control blocks are allocated in 31 bit system Getvis.
If you Fast Service Upgrade (FSU) from z/VSE 4.2 the default is IODEV=1023,
that is I/O control blocks are allocated in 24 bit system Getvis;
for z/VSE 4.3 or z/VSE 5.1 initial installation it is set to IODEV=1024.
Please consult your vendors, if they have a dependency on IODEV settings.
... and ensure, that you are on the latest PTF level (check for 31 bit
related VSAM and Supervisor PTFs).
Now you should have some 24 bit relief.
Next you should check your shared area settings via the Attention Routine (AR)
commands MAP SVA and GETVIS SVA.
It may be necessary to increase the shared area (31 bit).
You can do this by adapting the IPL SVA command (PSIZE, GETVIS parameters).
If there is more space in the shared areas (24 bit) than you need, you may
reduce the PSIZE/GETVIS values.
Please consider that you may need to adapt the VSIZE and page dataset,
if you increase the shared area (31 bit).
After you freed up some shared area (24 bit) space, you will see more
24 bit partition space for your applications.
You may consult the z/VSE Planning manual for details.
As always - plan for a regression test, if you change your system
before you go into production.