AIX virtual memory
Whenever a process gets virtual memory from the operating system, it can not return it. It can re-use the memory for other purposes but the size of the memory allocated to that process never decreases. A process is not allowed to exceed its memory allotment.
A process's memory allotment, the actual amount of virtual memory it can be allocated,
is defined by the ulimit -d (data) value. A machine-wide ulimit -d setting is defined in the
/etc/security/limits file and the default is 256MB. The ulimit -d value can be changed either machine-wide by changing the
/etc/security/limits file or for a specific process by using the ulimit -d command. Sufficient authorization is required to change the ulimit.
The ulimit -d value can be raised to unlimited. A value of unlimited leaves the maximum memory a process can obtain up to the process's memory model.
The InfoPrint Manager pdserver manipulates large amounts of data so it is built to exploit the Large Program support. Each pdserver can be allotted up to four 256 MB segments by the O/S. Therefore, if the ulimit -d value is set to unlimited, the pdserver can obtain up to 2 GB of virtual memory.