Memory usage is misleading

[frol]

There was a long-standing bug in Docker stats util (moby/moby#10824), which included caches into the memory usage reporting. While it was fixed recently in Docker 17.06 (docker/cli#80), ctop is still affected by the issue.

I think it is worth porting the new way of memory usage reporting from the docker/cli#80.

[bcicen]

@frol this is a simple enough change to make; however, I believe page cache is still counted toward a containers memory limit. This could cause confusion when diagnosing OOM events.

Perhaps a breakdown of total usage / page cache usage / total limit would be more transparent.

[frol]

Caches are not counted into the memory limit!

[bcicen]

See memory.limit_in_bytes

sets the maximum amount of user memory (including file cache)

[frol]

Well, that only means that the group cannot ever use more than that amount of memory, but the caches are automatically purged once more memory is allocated on heap.

[bcicen]

In the latest stable kernel and Docker-CE, I still don't see any circumstance where cache pressure and eviction is evaluated at a per-cgroup level; however, this is an issue to bring up with the Docker team.

For consistency, I've omitted cache from memory usage in 55a356b; to be included with the next relase