I got lot’s of results when searching but none of them gave me really concrete answers.
I have came to understand that the memory returned by the profiler in the editor is mostly useless - it just climbs and climbs quite happily by itself. Left for an hour and dozens of megabytes get swallowed up. But in reality running the game on Windows, or on Android, and using the task managers - shows no gain whatsoever (a relief compared to the near heart-attack on seeing the memory in the profiler soar ever skyward!).
Some have pointed to Sytem.GC.GetTotalMemory …but this only seems to return what C# is using (?). I.e. I create a load of mesh colliders to go with my meshes and since that’s handled by Unity internally I’m still using exactly the same memory as before. This isn’t a bad thing actually, as in theory it allows you to isolate memory leaks within your scripts that do not involve any Unity objects, textures and so on… assuming I understand System.GC.GetTotalMemory does indeed work happily in Unity.
However, other than that is there any other way to get an idea of memory usage? I have seen a script for a simple counting the number of objects and other stuff but that’s not really the same thing.
Sorry to digress here , but its very interesting, and it would seem to me that alot of Unitys in built Status displays are completely wrong. For eg : the FPS status is so blatantly wrong its not funny. The only thing i can assume is that the editor itself is somehow affecting the results, when actually entering play mode. I use a custom FPS meter , that is consistently always within a given range… and yet along side the Unity Stats window , Unity seems to think that the FPS is … well … its rediculous, it jumps around 100’s of frames per second at times, in the mean time , the custom FPS , stays completely stable as expected.
Yes, the Unity’s FPS value is misleading - but has been explained many times as that it measures the milliseconds it takes to render the graphics for that frame (and none of the scripting vsync or other tasks). In that sense some have argued it’s quite useful - but to display it as FPS just confuses, particulary as it’s at the top of the stats pane as a sort of headline figure. I suppose one could argue the same applies to the memory panel too… the headline figure is the total memory, just not of the game itself it seems. 
SO, back on topic - memory usage monitoring… any pointers?
I had never read anywhere this information, very good to know, thanks fanjules,
Why don’t you do a build, run it, alt-tab out and check Task Manager (win) or whatever you use for MacOS ?
Yep, as originally stated that’s one of the methods to confirm that my game wasn’t leaking memory (the other being Android’s task manager).
But it would be nice to have a real measure of memory usage breakdown rather than the current very limited options.
In fact, given the tight memory overhead of mobile devices, and the crashes that follow if you run too close to capacity (no swapfile remember!), one might ponder having additional info about memory usage is quite important.