Report memory stats using the same logic that docker uses for stats output; avoid extreme differences in output

server/environment_docker.go

@@ -501,7 +501,7 @@ func (d *DockerEnvironment) EnableResourcePolling() error {
 			}
 
 			s.Resources.CpuAbsolute = s.Resources.CalculateAbsoluteCpu(&v.PreCPUStats, &v.CPUStats)
-			s.Resources.Memory = v.MemoryStats.Usage
+			s.Resources.Memory = s.Resources.CalculateDockerMemory(v.MemoryStats)
 			s.Resources.MemoryLimit = v.MemoryStats.Limit
 
 			// Why you ask? This already has the logic for caching disk space in use and then
@@ -827,7 +827,6 @@ func (d *DockerEnvironment) exposedPorts() nat.PortSet {
 	return out
 }
 
-
 // Formats the resources available to a server instance in such as way that Docker will
 // generate a matching environment in the container.
 //

server/resources.go

@@ -9,7 +9,10 @@ import (
 // should obviously expect memory and CPU usage to be 0. However, disk will always be returned
 // since that is not dependent on the server being running to collect that data.
 type ResourceUsage struct {
-	// The total amount of memory, in bytes, that this server instance is consuming.
+	// The total amount of memory, in bytes, that this server instance is consuming. This is
+	// calculated slightly differently than just using the raw Memory field that the stats
+	// return from the container, so please check the code setting this value for how that
+	// is calculated.
 	Memory uint64 `json:"memory_bytes"`
 	// The total amount of memory this container or resource can use. Inside Docker this is
 	// going to be higher than you'd expect because we're automatically allocating overhead
@@ -28,6 +31,27 @@ type ResourceUsage struct {
 	} `json:"network"`
 }
 
+// The "docker stats" CLI call does not return the same value as the types.MemoryStats.Usage
+// value which can be rather confusing to people trying to compare panel usage to
+// their stats output.
+//
+// This math is straight up lifted from their CLI repository in order to show the same
+// values to avoid people bothering me about it. It should also reflect a slightly more
+// correct memory value anyways.
+//
+// @see https://github.com/docker/cli/blob/96e1d1d6/cli/command/container/stats_helpers.go#L227-L249
+func (ru *ResourceUsage) CalculateDockerMemory(stats types.MemoryStats) uint64 {
+	if v, ok := stats.Stats["total_inactive_file"]; ok && v < stats.Usage {
+		return stats.Usage - v
+	}
+
+	if v := stats.Stats["inactive_file"]; v < stats.Usage {
+		return stats.Usage - v
+	}
+
+	return stats.Usage
+}
+
 // Calculates the absolute CPU usage used by the server process on the system, not constrained
 // by the defined CPU limits on the container.
 //