QIO Configuration and Management Manual

Configuring the QIO Subsystem
QIO Configuration and Management Manual—424717-008
2-5
Memory Management
Memory Management
QIO is configured to run in user-addressable data space, but if your environment is a
NonStop S-series server and uses less than 128 MB of QIO shared memory or an
Integrity NonStop NS-series server and uses less than 256 MB of QIO shared memory,
HP recommends that you configure QIO to run in system data space (see Configuring
QIO to Reside in System Data Space on page 2-9). If you are going to leave QIO
running in user-addressable data space (the default configuration), be aware of the
potential memory conflicts that can occur. The rest of this subsection discusses these
potential conflicts.
Situations in Which Addressing Conflicts Can Occur
In extreme memory-use situations, problems can arise in user-addressable data
space. These problems are mostly related to memory conflicts and overlapping
addresses. This subsection discusses these situations and how to identify them.
Several common circumstances under which address conflicts can occur in the user-
addressable data space are:

If the process globals and process heap segment grows to the point where it
becomes filled

If you try to specify a program to a flat segment address that overlaps QIO space,
the allocation fails

If your program needs more than the available flat memory space and the process
globals and process heap space memory do not have room for it

If a program calls Parallel Library TCP/IP or NonStop TCP/IPv6,, the attachment of
the socket can be in QIO space. The socket call causes the attachment of the QIO
segment. A conflict occurs if another address space occupied by QIO is already
allocated to either heap space or another flat segment.
Memory Management Considerations
If you want to run QIO in user-addressable data space, watch for these symptoms of
memory-management problems:

Does the user application fail to attach to the QIO segment?

Does the user application use a large amount of process heap space?

Does the user application create its own flat segments, and, if so, where is a base
address specified in the segment call?
Use the STATUS SEGMENT, DETAIL command to display information about your QIO
process. (For more information, see Determining the Maximum Pool Size
on page 2-6.)
Note. A memory-related error message is generated in these situations.