How can System Monitor report that a process is using less memory than the sum of its child processes'?

I’m trying to remediate Consistent but random stutter diagnosis - Firefox Nightly - Mozilla Discourse, and in doing so, have been using plasma-systemmonitor more than I usually do, especially focussing upon the accuracy of its memory usage reporting.

Consequently, I’ve noticed that although

demonstrates that Firefox is somehow using an ungodly 13.6 GiB of memory, the detailed process breakdown reports that it’s using merely 600 MiB despite one of its immediate child processes using 1.3 GiB!

What? Do I not understand math?

TL;DR: No.

Imagine a big red ring around the 13GiB

Now imagine a big red ring round the 695MiB, the 1.3GiB, the 930, the 728… down to the bottom where the next application is (Steam?)

Get a responsible adult with a calculator to help you add all the numbers in the second ring together…

Is the total somewhere about the same as the number in the first red ring?

@Angus, I believe that you’ve conflated the screenshots. Obviously, if I add all of the memory usage values of the child processes of firefox in

to one another, their sum doesn’t add to 695.7 MiB. Instead, they would add, if all were visible, to something similar to 13.5. Hence the question.

So what is your question?

draw some red rings round the numbers that you believe are at fault, and explain why.

Absolutely no reason to be an a** about it.

You misunderstand the numbers.
The application (picture 1) shows the total amount of memory everything around firefox consumes.

In the second picture, firefox is the shown as the process firefox, and below all the other stuff connected to firefox and how much memory they consume.

If you take the memory consumed by firefox on the second picture, then add together ALL the suff below in that tree, you will end up with the number shown in picture 1. Or at least you should… xD

Also, dont forget that one gibibyte (GiB) is 1024 mebibytes (MiB), not 1000.

I’ve already said that - apparently that is not the issue.

@bedna, so although the child processes might add to 13 GiB, the process tree view displays solely the memory being used by that that process, excluding its children?

Yeah, don’t worry — since the SI and IETF have finally got their act together, formally separating the base-10 and base-2 measurement systems, it’s actually the system taught in schools now (albeit inconsistently, as expected) so I’ve been using both my whole life.


If you refer to the 695.7MiB, yes.

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