The "z1090instcheck" command suggests:

NOTE

shmmax should be greater than 1.1 times the sum
of z memory (as specified in your devmap) for
ALL your 1090 instances.

This appears to be in keeping with guidance in the ZPDT Volume 2 Redbook.

However, in the zPDT Volume 1 Redbook it states:

The memory statement specifies the size of the System z memory to be used for 1090
operation. For performance reasons the real memory size of the PC should be at least
500 MB greater than the memory parameter. The number specified must be smaller than the
maximum shared memory value specified for Linux; this is set by the kernel.shmmax
parameter in Linux.

Which might contradict Volume 2. Which guidance is more accurate? What are
the considerations for shared Linux memory requirements as System z memory increases?
And how does this relate to the real memory size of the PC?

David,

kernel.shmmax specifies the maximum amount of linux shared memory available to a single process. Since z/OS real memory and some z1090 work areas are in linux shared memory, you must set kernel.shmmax to a value larger than the value you specify in the devmap. Since the amount of storage required for base linux can vary, we also recommend that to be on the safe side that you reserve at least 500 MB of storage for base linux.

For example. 32 GB total memory available on box
maximum available memory for z1090 and z/OS would be 31.5 GB, 500 MB less than total memory available.
kernel.shmmax would specify:
kernel.shmmax=31500000000 (28,636,363,636 * 1.1)
devmap would specify:
memory 28636M (smaller values are ok)

Additional parameters such as kernel.shmall are relevant if running more than one UT instance on the same box. Note we do not recommend multiple UT instances on the same box at this time.

Thanks, John.

To make sure, is the following interpretation correct?

For every 10GB of z/OS memory, RDz UT requires an additional 1.1GB of Linux shared memory
for its work areas.

10GB would require 1.1GB of Linux shared memory, for a total of 11.1GB, and 30GB would require
an additional 3.3GB, for a total of 33.3GB.

Added to that total, at least 500MB is required for Linux to operate. Is it possible that this
number could exceed 500MB depending on the software stack being run (e.g, backup, monitoring,
etc.)?

And all the memory required, for RDz UT and Linux, cannot exceed the physical memory
available on the box.

Is there a native Linux command that would give an overall picture of memory consumption
on a Linux machine, to verify how the memory is actually being consumed?

Total memory = Linux memory + z1090 memory

Linux memory = memory required by all native linux processes including z1090

z1090 memory = z/OS real memory * 1.1

From my previous example:

32 GB total memory available on box
500 MB Linux memory reserved for native linux processes
maximum available memory for z1090 and z/OS would be 31.5 GB
kernel.shmmax would specify:
kernel.shmmax=31500000000 (28,636,363,636 * 1.1)
devmap would specify:
memory 28636M (31500000000 / 1.1)

More native linux processes = potentially more required native linux memory and less available of the total for z1090 and z/OS. We do not, however, recommend any other Linux processes run on the UT machine aside from the z1090 system environment.

RDz John