[BUG] Incorrect memory usage when zram is enabled

[thefossguy]

Describe the bug

The way that used memory size is being calculated presently seems to be indirectly adding the total zram swap size in it too. This results in the incorrect total usage metric for the actual memory usage

To Reproduce

Run btop with zram swap enabled.

Expected behavior

Do not consider the size of zram swap in total memory usage.

Screenshots

Info (please complete the following information):

• btop++ version: 1.2.13
• Binary: from nixpkgs and also "hand-compiled"
• Architecture: present on x86_64 and aarch64
• Platform: Linux
• (Linux) Kernel: 6.8.1

[thefossguy]

I'm not familiar enough with the codebase, nor do I use C++ enough to send a PR. But here is how the free utility from the procps set of utilities calculates the used memory value: https://gitlab.com/procps-ng/procps/-/blob/9ebc09e15a73cb3996b0fcdb571f134626ec3264/library/include/meminfo.h#L94