Originally posted by: SystemAdmin
If you want to estimate the memory utilization of the system as a whole (as opposed to that of one or more processes) you've set yourself a difficult task. AIX is unlike other Unices in how it utilizes memory. Specifically it tries to fill up all the available physical memory with something all the time. So, if you look at the system with vmstat, topas, nmon or whatever you'll most likely see memory % utilization at or near 100% all the time. This is because after all the working set pages are allocated AIX fills up the rest with file pages, a.k.a. non-computational pages. So, if you're trying to figure out whether memory is over-committed your best bet is to look at the "paging space paging" numbers. These are the ones shown as PI and PO on vmstat output. If memory is undercommitted these numbers should be zero, or nearly zero, all the time. If you see numbers higher than low single digits steadily over time, then you're low on memory.
HTH
Jim Lane
#AIX-Forum