--- /dev/null	2020-02-11 09:31:42.601809740 +0100
+++ new/src/java.base/linux/classes/jdk/internal/platform/CgroupSubsystemFactory.java	2020-02-11 18:28:53.161662042 +0100
@@ -0,0 +1,135 @@
+/*
+ * Copyright (c) 2020, Red Hat Inc.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.  Oracle designates this
+ * particular file as subject to the "Classpath" exception as provided
+ * by Oracle in the LICENSE file that accompanied this code.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+package jdk.internal.platform;
+
+import java.io.IOException;
+import java.lang.System.Logger;
+import java.lang.System.Logger.Level;
+import java.nio.file.Paths;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.Collectors;
+import java.util.stream.Stream;
+
+import jdk.internal.platform.cgroupv1.CgroupV1Subsystem;
+import jdk.internal.platform.cgroupv2.CgroupV2Subsystem;
+import jdk.internal.platform.cgroupv2.CgroupV2SubsystemController;
+
+class CgroupSubsystemFactory {
+
+    private static final String CPU_CTRL = "cpu";
+    private static final String CPUACCT_CTRL = "cpuacct";
+    private static final String CPUSET_CTRL = "cpuset";
+    private static final String BLKIO_CTRL = "blkio";
+    private static final String MEMORY_CTRL = "memory";
+
+    static CgroupMetrics create() {
+        Map<String, CgroupInfo> infos = new HashMap<>();
+        try {
+            List<String> lines = CgroupUtil.readAllLinesPrivileged(Paths.get("/proc/cgroups"));
+            for (String line : lines) {
+                if (line.startsWith("#")) {
+                    continue;
+                }
+                CgroupInfo info = CgroupInfo.fromCgroupsLine(line);
+                switch (info.getName()) {
+                case CPU_CTRL:      infos.put(CPU_CTRL, info); break;
+                case CPUACCT_CTRL:  infos.put(CPUACCT_CTRL, info); break;
+                case CPUSET_CTRL:   infos.put(CPUSET_CTRL, info); break;
+                case MEMORY_CTRL:   infos.put(MEMORY_CTRL, info); break;
+                case BLKIO_CTRL:    infos.put(BLKIO_CTRL, info); break;
+                }
+            }
+        } catch (IOException e) {
+            return null;
+        }
+
+        // For cgroups v1 all controllers need to have non-zero hierarchy id
+        boolean isCgroupsV2 = true;
+        boolean anyControllersEnabled = false;
+        boolean anyCgroupsV2Controller = false;
+        boolean anyCgroupsV1Controller = false;
+        for (CgroupInfo info: infos.values()) {
+            anyCgroupsV1Controller = anyCgroupsV1Controller || info.getHierarchyId() != 0;
+            anyCgroupsV2Controller = anyCgroupsV2Controller || info.getHierarchyId() == 0;
+            isCgroupsV2 = isCgroupsV2 && info.getHierarchyId() == 0;
+            anyControllersEnabled = anyControllersEnabled || info.isEnabled();
+        }
+
+        // If no controller is enabled, return no metrics.
+        if (!anyControllersEnabled) {
+            return null;
+        }
+        // Warn about mixed cgroups v1 and cgroups v2 controllers. The code is
+        // not ready to deal with that on a per-controller basis. Return no metrics
+        // in that case
+        if (anyCgroupsV1Controller && anyCgroupsV2Controller) {
+            Logger logger = System.getLogger("jdk.internal.platform");
+            logger.log(Level.WARNING, "Mixed cgroupv1 and cgroupv2 not supported. Metrics disabled.");
+            return null;
+        }
+
+        if (isCgroupsV2) {
+            // read mountinfo so as to determine root mount path
+            String mountPath = null;
+            try (Stream<String> lines =
+                    CgroupUtil.readFilePrivileged(Paths.get("/proc/self/mountinfo"))) {
+
+                String l = lines.filter(line -> line.contains(" - cgroup2 "))
+                                .collect(Collectors.joining());
+                String[] tokens = l.split(" ");
+                mountPath = tokens[4];
+            } catch (IOException e) {
+                return null;
+            }
+            String cgroupPath = null;
+            try {
+                List<String> lines = CgroupUtil.readAllLinesPrivileged(Paths.get("/proc/self/cgroup"));
+                for (String line: lines) {
+                    String[] tokens = line.split(":");
+                    if (tokens.length != 3) {
+                        return null; // something is not right.
+                    }
+                    if (!"0".equals(tokens[0])) {
+                        // hierarchy must be zero for cgroups v2
+                        return null;
+                    }
+                    cgroupPath = tokens[2];
+                    break;
+                }
+            } catch (IOException e) {
+                return null;
+            }
+            CgroupSubsystemController unified = new CgroupV2SubsystemController(
+                    mountPath,
+                    cgroupPath);
+            return new CgroupMetrics(new CgroupV2Subsystem(unified));
+        } else {
+            return new CgroupV1Metrics(CgroupV1Subsystem.getInstance());
+        }
+    }
+}