QIO Configuration and Management Manual

Configuring the QIO Subsystem
QIO Configuration and Management Manual—424717-008
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QIO Shared Flat Memory and QIO IOperm Segment
The process globals space and the process heap space are cleared when the program
exits.
QIO Shared Flat Memory and QIO IOperm Segment
The QIO memory segment within the user-addressable data space has a default size
of 512 MB, which is also its maximum size. QIO memory is followed by 32 MB of
IOperm memory, which is space in flat segment memory to provide an aliased memory
space. The total QIO memory segment is 544 MB.
The QIO memory segment and IOperm space starts at base address 0x20000000 and
ends at the address 0x42000000.
These addresses were chosen to:

Put the QIO and IOperm segments close to the middle of the data segment area
for native processes

Provide space for the heap growth

Provide space for the creation of other flat segments without conflict
When a process uses the QIO shared memory subsystem with the default values, the
QIO shared memory becomes a part of the process’s address space.
Flat Segment Memory Space and Unassigned Flat Memory
Space
The remaining user-addressable data space is available to programs for storing
process-defined segments. The flat, unassigned space between the end of the QIO
memory segment and the default start of flat segment memory is available for the flat
segment memory to grow into.
When the flat segment memory space and the unassigned flat memory space are full,
the flat segment memory begins to use empty space in the process globals and
process heap segment space. If flat segment space cannot be allocated because there
is not enough unassigned space, memory problems can occur.
The following subsection describes how you can manage memory within
user-addressable data space.