AIX

svmon -p
ps -efZ
lsps -a
lsps -s
check this

Use topas command.It will be similar to top in Linux

In AIX now you will find that the memory of a system is almost constantly filled to capacity. Even if currently running programs do not consume all available memory, the operating system retains in memory the text pages of programs that ran earlier and the files that they used. There is no cost associated with this retention, because the memory would have been unused anyway. In many cases, the programs or files will be used again, which reduces disk I/O.

If there is a demand on more memory the system will just realocat as required

ALSO you can have a look at NMON

Also, if you look at the AVM column in vmstat output, you get the amount of memory in 4K pages used by processes for their working sets. If this is relatively constant over time, it gives you a pretty good indication of what is really being used for processes, as opposed to file caching. In an LPAR, you can reduce the allocated memory until the system starts to page, then raise it a bit. The AVM column gives you a good place to start with this number. This all assumes a static workload, of course. And databases complicate the matter further.