Expose proportional resident memory size

[PierreF]

Currently the resident size is the sum of resident size from all process in the group, which will means a rather high value for processed that share significant amount of memory.

Linux do expose a proportional resident memory size in the smaps file, which is

The "proportional set size" (PSS) of a process is the count of pages it has
in memory, where each page is divided by the number of processes sharing it.

I think the sum of PSS is more interesting than sum of RSS, as RSS sum is way too high.

I'm willing to come with a PR, but that need update on procfs dependency and before working on this, I want to known your thought on whether this change should be done on your procfs fork or being submitted to prometheus/procfs and stop using the forked-procfs ? It seems that prometheus/procfs now has ProcStatus support which was the reason of the fork.

[flixr]

I'm also seeing this issue, but didn't quite spend enough time to find out where this is coming from...
But "correct" reporting of this would be very very welcome!

[PierreF]

I'll start working on PRs to provide this by using prometheus/procfs, that is:

• submit PR here to use prometheus/procfs instead of ncabatoff/procfs
• submit PR on prometheus/procfs to export smaps information
• submit PR here to using smaps information from prometheus/procfs. This PR will depend on the two above.

[PierreF]

PRs created:

• wchan gathering was missing on prometheus/procfs => PR Add wchan. prometheus/procfs#280
• Using prometheus/procfs (which require above PR): Use github.com/prometheus/procfs #141
• Added gathering of smaps in prometheus/procfs => Add ProcSMaps from smaps file prometheus/procfs#281
• Final PR (which require all above PRs): Add proportional resident memory size #142