Created attachment 697523 [details]
screenshots of system monitor and "free" side by side contradicting each other

I run Xfce. Since that is known for its low memory usage, I was surprised to
find that, according to mate-system-monitor, It uses about 900 MB with no apps
open.

That seemed odd, so I opened my terminal and ran the "free" command. Now of
course the total reported memory usage will be much from what the graphical app
gives since it includes memory that the kernel is using for disk cache. That's
not surprising.

But what is surprising is that the "-/+ buffers/cache" line below it, which is
supposed to be the "true" memory usage and presumably the same thing that the
graphical app is supposed to give a reading of, is 300 MB lower than what the
graphical app is reporting. It was giving roughly 600MB, while the graphical
app was giving roughly 900.

I installed gnome-system-monitor to see if it displayed the same behavior. It
did, exactly the same as the MATE version. I tried opening a bunch of apps to
drive the memory usage up, and the discrepancy seemed to remain fixed at
roughly 300MB of difference between the graphical app and "free".

Screenshots of these experiments are attached.