If you have ever looked at the ps(1) output on an AIX box and wondered why the virtual memory size (VSZ) is so small, often even smaller then the resident set size (RSS), then here's the answer: it's not the virtual memory size. It is actually the size of the data section of the virtual memory of the process.
If you really do want to know the VSZ of a process you'll have to use svmon -P 123, there you will find it. But do multiply this by the pagesize ( pagesize(1) is a user tool on AIX). If only somehow this would be documented.
Oh, and if someone knows where the source of svmon lives I'd love to know how they actually find that, using the struct procent64 structure from procinfo.h I can not figure out a way of finding it. And the VSZ information in /proc/123/psinfo is completely whacky, no idea what that is supposed to be.
For completeness sake: this is on AIX 5.3.