The memory information reported by the supervisor currently
estimates the value of used memory as `MemTotal - MemFree`.
However, linux systems will try to cache and buffer as much
memory as possible, which will affect the output of `MemFree`
(from /proc/meminfo) and in consequence the memory usage seen
by the user on the dashboard, which will appear much greater than
it is.
The correct calculation should be `MemTotal - MemFree - Buffers - Cached`,
which the calculation performed by `htop` and the `free` commands.
Change-type: patch
Signed-off-by: Felipe Lalanne <felipe@balena.io>
Connects-to: #1471
