How do you detect memory issues ?

How do you detect memory issues ?

I always used "*po" or "paged outs*". Now on Amazon Linux I don't see "po" but there is "bo" (blocks written out). In past, at least on OSF & Ultrix, page outs were a sign of needed memory that was written out to disk and when I needed that memory it would take a big performance hit to read it in. Thus "po" was a good canary on the coal mine. Any consistent values over over say 10 were a sign.

Some people use "*scan rate*" but I never found that as easy to interpret as page outs. Again what values would you use

Some suggest using freeable memory as a yardstick where freeable is "free" + "cached" or MemFree + Cached + Inactive. Even in this case what would you use for values to alert on?

I've always ignored swap stats as if you are swapping it is too late.

What do you use to detect memory issues ?