Activity Monitor, Memory Used on Apple Silicon

[pipo2]

Something I always wanted to ask since Apple Silicon computers.
Activity Monitor -> Memory.
What makes the 'Memory Used:' bigger than the sole addition of its shown components?

Right now on my M1:
App Memory: 5.27 + Wired Memory: 1.25 + Compressed: 0 = Memory Used: 7.63 (of course not).

Others like BigBlur in the memory-leaks-in-15-3-1 thread:
App Memory: 17.05 + Wired Memory: 2.23 + Compressed: 2.46 = Memory Used: 24.82 (again huh?).

On MacIntels, this doesn't happen AIR, 'Memory Used:' is the same as the addition of its shown components.
My take sofar is that the graphic system on AS shares/eates from the same memory pool.
But then, why not just show it. This looks a bit silly...

Apple doesn't mention it: https://support.apple.com/guide/activity-monitor/view-memory-usage-actmntr1004/mac

Or it is a plain bug, (still) not fixed. Can happen...

Just curious, regards.

 

[gilby101]

This looks a bit silly...

Very silly - you would expect a computer to do simple arithmetic. Even with Intel Macs, the numbers don't quite add up. For Mx Macs, the disparity is hilarious/ridiculous.

My take: Memory management is a complex task and counting the state of individual pages is not simple. There are numerous internal counters and AM presents a very simplified view. And this is made worse by the unified memory structures in Mx Macs. AM really does need an update.

Third party apps (e.g. iStat Menus) are no better.

You will get a more consistent view by using the output from the command vm_stat. But even that doesn't help with the chunk of memory used as "unified memory".