stats: get the memory limit from the spec

OCI runtimes may set the memory limits in different ways, e.g., crun
creates a sub-cgroup where the limits are applied, while runc applies
them directly on the created cgroup.  Since there is standardization
on the cgroup path to use, just use the limit specified in the spec
file.

Signed-off-by: Giuseppe Scrivano <[email protected]>

libpod/stats.go

@@ -3,6 +3,7 @@
 package libpod
 
 import (
+	"math"
 	"strings"
 	"syscall"
 	"time"
@@ -68,7 +69,7 @@ func (c *Container) GetContainerStats(previousStats *define.ContainerStats) (*de
 	stats.AvgCPU = calculateAvgCPU(stats.CPU, previousStats.AvgCPU, previousStats.DataPoints)
 	stats.DataPoints = previousStats.DataPoints + 1
 	stats.MemUsage = cgroupStats.Memory.Usage.Usage
-	stats.MemLimit = getMemLimit(cgroupStats.Memory.Usage.Limit)
+	stats.MemLimit = c.getMemLimit()
 	stats.MemPerc = (float64(stats.MemUsage) / float64(stats.MemLimit)) * 100
 	stats.PIDs = 0
 	if conState == define.ContainerStateRunning || conState == define.ContainerStatePaused {
@@ -91,22 +92,29 @@ func (c *Container) GetContainerStats(previousStats *define.ContainerStats) (*de
 	return stats, nil
 }
 
-// getMemory limit returns the memory limit for a given cgroup
-// If the configured memory limit is larger than the total memory on the sys, the
-// physical system memory size is returned
-func getMemLimit(cgroupLimit uint64) uint64 {
+// getMemory limit returns the memory limit for a container
+func (c *Container) getMemLimit() uint64 {
+	memLimit := uint64(math.MaxUint64)
+
+	if c.config.Spec.Linux != nil && c.config.Spec.Linux.Resources != nil &&
+		c.config.Spec.Linux.Resources.Memory != nil && c.config.Spec.Linux.Resources.Memory.Limit != nil {
+		memLimit = uint64(*c.config.Spec.Linux.Resources.Memory.Limit)
+	}
+
 	si := &syscall.Sysinfo_t{}
 	err := syscall.Sysinfo(si)
 	if err != nil {
-		return cgroupLimit
+		return memLimit
 	}
 
 	//nolint:unconvert
 	physicalLimit := uint64(si.Totalram)
-	if cgroupLimit > physicalLimit {
+
+	if memLimit <= 0 || memLimit > physicalLimit {
 		return physicalLimit
 	}
-	return cgroupLimit
+
+	return memLimit
 }
 
 // calculateCPUPercent calculates the cpu usage using the latest measurement in stats.