Figuring out if you can use more memory.

My preferred tool is the Terminal and vm_stat. I run vm_stat at one minute intervals, and watch the last column (pageout).

vm_stat 60
free active inac … pageins pageout
59987 399329 133050 … 326794 88547
59858 399326 133181 … 0 0
59673 399324 133369 … 0 0
59567 399323 133475 … 0 0
59665 399288 133377 … 1 0
60113 399325 133055 … 0 0
59953 399324 133087 … 0 0
59818 399475 133224 … 0 0
59588 399473 133457 … 0 0
59496 399472 133549 … 0 0
59485 399473 133560 … 0 0
59715 399472 133458 … 0 0
59584 399473 133461 … 0 0
59583 399474 133462 … 0 0
59583 399319 133462 … 0 0
59578 399474 133467 … 0 0
59871 397223 133165 … 10 0

This will give you an over time view of your memory usage.

The last column, pageout, is telling you when your system is using more memory than your system has. And pageouts are disk I/O which is slower than having stuff in memory.

If you have lots of zeros during normal usage, then your system has sufficient memory.

If you have momentary bursts of pageout activity, then most likly you are still OK.

If you have heavy pageout activity during normal usage, then this is a good indication that your system could benefit from having more memory.

And the beauty of vm_stat, is that you can run this in a terminal window, and then hide the window while it collects information.

I personally used this method on an older 450MHz G4 system having 640MB, and I would notice heavy pageout activity when I would switch windows, and I was also noticing that switching windows was slow. I upgrade that system to 1.5GB and my pageout activity dropped to mostly zero, and switching windows was much more responsive.

Of course that system has been retired and I use a PowerMac G5 with 2.5GB and it almost never pages. And my new MacBook Core 2 Duo has 2GB, and it doesn’t page either

Anyway, I strongly suggest trying vm_stat 60 to decide if your performance issues are memory related.

Bob Harris