[saagarjha]

As far as I can tell, Activity Monitor and footprint(1) both grab the phys_footprint field from proc_pid_rusage. I have not seem them diverge yet, so if there is more to this that I am missing I (as the author of a system monitoring tool of this sort) would be interested in hearing about it.

[astrange]

See "there’s more columns than that". The single process "memory" column does match but AM doesn't show coalition (multiple process) memory totals, the compressed column is an estimate, footprint --vmObjectDirty also exists and is a valid way to look at things, etc.

[saagarjha]

Ah, I see what you mean now; yes, it's not reliable in the sense that there are ways to measure it that look a little harder. That being said, I'm not sure I'd classify it as "inaccurate"–it has, in my experience at least, been a fairly good first approximation of memory usage.