drivers/docker: account for cgroup-v2 memory stats

If the docker engine is running on cgroup-v2 host, then RSS and Max
Usage doesn't get reported.

Using a heauristic here to avoid adding more API calls to the Docker
Engine to infer cgroups version. Also, opted to avoid coordinating stats
collection with fingerprinting, which adds concurrency complexities.

drivers/docker/util/stats_posix.go

@@ -12,17 +12,28 @@ import (
 
 var (
 	DockerMeasuredCPUStats = []string{"Throttled Periods", "Throttled Time", "Percent"}
-	DockerMeasuredMemStats = []string{"RSS", "Cache", "Swap", "Usage", "Max Usage"}
+
+	// cgroup-v2 only exposes a subset of memory stats
+	DockerCgroupV1MeasuredMemStats = []string{"RSS", "Cache", "Swap", "Usage", "Max Usage"}
+	DockerCgroupV2MeasuredMemStats = []string{"Cache", "Swap", "Usage"}
 )
 
 func DockerStatsToTaskResourceUsage(s *docker.Stats) *cstructs.TaskResourceUsage {
+	measuredMems := DockerCgroupV1MeasuredMemStats
+
+	// use a simple heauristic to check if cgroup-v2 is used.
+	// go-dockerclient doesn't distinguish between 0 and not-present value
+	if s.MemoryStats.Stats.Rss == 0 && s.MemoryStats.MaxUsage == 0 && s.MemoryStats.Usage != 0 {
+		measuredMems = DockerCgroupV2MeasuredMemStats
+	}
+
 	ms := &cstructs.MemoryStats{
 		RSS:      s.MemoryStats.Stats.Rss,
 		Cache:    s.MemoryStats.Stats.Cache,
 		Swap:     s.MemoryStats.Stats.Swap,
 		Usage:    s.MemoryStats.Usage,
 		MaxUsage: s.MemoryStats.MaxUsage,
-		Measured: DockerMeasuredMemStats,
+		Measured: measuredMems,
 	}
 
 	cs := &cstructs.CpuStats{