Metricbeat - collects the dockers memory size which is different from “docker stats”

[SperChung-11]

Hi，I have met a problem as follows：

i have use metricbeat to collect docker memory, but found that the data of memory (suce as memory usage) was different from the "docker stats", is it right ?
metricbeat: 7.6.0

[elasticmachine]

Pinging @elastic/integrations (Team:Integrations)

[ChrsMark]

cc: @fearful-symmetry

[fearful-symmetry]

So, I did some digging, and there's actually a fair bit of difference between how we calculate percentages, and I'm guessing that our implementation is based on an outdated version of what docker did. We just do metric/memory_limit for any given memory value, but docker is (now) just a tad more sophisticated:

	// cgroup v1
	if v, isCgroup1 := mem.Stats["total_inactive_file"]; isCgroup1 && v < mem.Usage {
		return float64(mem.Usage - v)
	}
	// cgroup v2
	if v := mem.Stats["inactive_file"]; v < mem.Usage {
		return float64(mem.Usage - v)
	}
	return float64(mem.Usage)

I'm leaning towards calling this a bug, based on how other platforms.