cgroups: fix memory usage on cgroup v1

calculate the memory usage on cgroup v1 using the same logic as cgroup
v2.

Since there is no single "anon" field, calculate the memory usage by
summing the two fields "total_active_anon" and "total_inactive_anon".

Closes: #1642

[NO NEW TESTS NEEDED]

Signed-off-by: Giuseppe Scrivano <gscrivan@redhat.com>

pkg/cgroups/memory_linux.go

@@ -4,7 +4,9 @@
 package cgroups
 
 import (
+	"fmt"
 	"path/filepath"
+	"strconv"
 
 	"github.com/opencontainers/runc/libcontainer/cgroups"
 	"github.com/opencontainers/runc/libcontainer/cgroups/fs"
@@ -63,9 +65,26 @@ func (c *linuxMemHandler) Stat(ctr *CgroupControl, m *cgroups.Stats) error {
 	} else {
 		memoryRoot = ctr.getCgroupv1Path(Memory)
 		limitFilename = "memory.limit_in_bytes"
-		if memUsage.Usage.Usage, err = readFileAsUint64(filepath.Join(memoryRoot, "memory.usage_in_bytes")); err != nil {
+
+		path := filepath.Join(memoryRoot, "memory.stat")
+		values, err := readCgroupMapPath(path)
+		if err != nil {
 			return err
 		}
+
+		// cgroup v1 does not have a single "anon" field, but we can calculate it
+		// from total_active_anon and total_inactive_anon
+		memUsage.Usage.Usage = 0
+		for _, key := range []string{"total_active_anon", "total_inactive_anon"} {
+			if _, found := values[key]; !found {
+				continue
+			}
+			res, err := strconv.ParseUint(values[key][0], 10, 64)
+			if err != nil {
+				return fmt.Errorf("parse %s from %s: %w", key, path, err)
+			}
+			memUsage.Usage.Usage += res
+		}
 	}
 
 	memUsage.Usage.Limit, err = readFileAsUint64(filepath.Join(memoryRoot, limitFilename))