kube-capacity | simple CLI that provides an overview of the resource | Command Line Interface library

The ps does not reflect the actual amount of memory used by the application but only the memory reserved for it. It can be very misleading if pages are shared by several processes or by using some dynamically linked libraries.

Understanding memory usage on Linux is a very good article describing how memory usage in Linux works and what ps is actually reporting.

Why ps is "wrong"

Depending on how you look at it, ps is not reporting the real memory usage of processes. What it is really doing is showing how much real memory each process would take up if it were the only process running. Of course, a typical Linux machine has several dozen processes running at any given time, which means that the VSZ and RSS numbers reported by ps are almost definitely wrong.

That is why ps should not be used for some detailed data for memory consumption.

Alternative to ps would be smem. It reports physical memory usage, taking shared memory pages into account. Then unshared memory is reported at the USS (Unique Set Size). So you can use USS when you want to ignore shared memory.

The unshared memory (USS) plus process's proportion of shared memory is reported at the PSS (Proportionial Set Size). Basically it add USS along with a proportion of its shared memory divided by the number of processes sharing that memory.

On the other hand RSS(Resident Set Size) is the amount of shared memory plus unshared memory used by each process. If any processes share memory, this will short report that over the amount of memory that is actually used.

Linux uses a resource management technique used in programming to efficiently implement a duplicate or copy operation. This is called copy-on-write. So when you have parent and child process, they both will show the same RSS. With copy-on-write linux ensures that both processes are really using the same memory.