[cgroups2] Use OomListener in MemoryControllerProcess.

The MemoryControllerProcess needs an OomListener to ensure that it does
not need to listen for oom events by polling, which causes race
conditions with the oom killer.

We spawn an OomListener in the MemoryControllerProcess and use it
to listen for oom events in any cgroup via oomListen().

Review: https://reviews.apache.org/r/75185/

src/slave/containerizer/mesos/isolators/cgroups2/controllers/memory.cpp

@@ -35,6 +35,7 @@ using process::PID;
 using process::Owned;
 
 using cgroups2::memory::Stats;
+using cgroups2::memory::OomListener;
 
 using mesos::slave::ContainerConfig;
 using mesos::slave::ContainerLimitation;
@@ -48,13 +49,22 @@ namespace slave {
 
 Try<Owned<ControllerProcess>> MemoryControllerProcess::create(const Flags& flags)
 {
-  return Owned<ControllerProcess>(new MemoryControllerProcess(flags));
+  Try<OomListener> listener = OomListener::create();
+  if (listener.isError()) {
+    return Error(
+        "Could not create oom listener for MemoryControllerProcess: "
+        + listener.error());
+  }
+  return Owned<ControllerProcess>(
+      new MemoryControllerProcess(flags, std::move(*listener)));
 }
 
 
-MemoryControllerProcess::MemoryControllerProcess(const Flags& _flags)
+MemoryControllerProcess::MemoryControllerProcess(
+    const Flags& _flags,  OomListener&& _oomListener)
   : ProcessBase(process::ID::generate("cgroups-v2-memory-controller")),
-    ControllerProcess(_flags) {}
+    ControllerProcess(_flags),
+    oomListener(std::move(_oomListener)) {}
 
 
 string MemoryControllerProcess::name() const
@@ -277,7 +287,7 @@ void MemoryControllerProcess::oomListen(
     return;
   }
 
-  infos[containerId].oom = cgroups2::memory::oom(cgroup);
+  infos[containerId].oom = oomListener.listen(cgroup);
 
   LOG(INFO) << "Listening for OOM events for container "
             << containerId;

src/slave/containerizer/mesos/isolators/cgroups2/controllers/memory.hpp

@@ -25,6 +25,7 @@
 
 #include "slave/flags.hpp"
 #include "slave/containerizer/mesos/isolators/cgroups2/controller.hpp"
+#include "linux/cgroups2.hpp"
 
 namespace mesos {
 namespace internal {
@@ -85,7 +86,9 @@ class MemoryControllerProcess : public ControllerProcess
     bool hardLimitUpdated = false;
   };
 
-  MemoryControllerProcess(const Flags& flags);
+  MemoryControllerProcess(
+      const Flags& flags,
+      cgroups2::memory::OomListener&& oomListener);
 
   void oomListen(
       const ContainerID& containerId,
@@ -97,6 +100,8 @@ class MemoryControllerProcess : public ControllerProcess
       const process::Future<Nothing>& oomFuture);
 
   hashmap<ContainerID, Info> infos;
+
+  cgroups2::memory::OomListener oomListener;
 };
 
 } // namespace slave {