Addendum patch for YARN-5731

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/ProportionalCapacityPreemptionPolicy.java

@@ -231,28 +231,13 @@ public class ProportionalCapacityPreemptionPolicy
           .add(new ReservedContainerCandidatesSelector(this));
     }
 
+    boolean additionalPreemptionBasedOnReservedResource = csConfig.getBoolean(
+        CapacitySchedulerConfiguration.ADDITIONAL_RESOURCE_BALANCE_BASED_ON_RESERVED_CONTAINERS,
+        CapacitySchedulerConfiguration.DEFAULT_ADDITIONAL_RESOURCE_BALANCE_BASED_ON_RESERVED_CONTAINERS);
+
     // initialize candidates preemption selection policies
-    // When select candidates for reserved containers is enabled, exclude reserved
-    // resource in fifo policy (less aggressive). Otherwise include reserved
-    // resource.
-    //
-    // Why doing this? In YARN-4390, we added preemption-based-on-reserved-container
-    // Support. To reduce unnecessary preemption for large containers. We will
-    // not include reserved resources while calculating ideal-allocation in
-    // FifoCandidatesSelector.
-    //
-    // Changes in YARN-4390 will significantly reduce number of containers preempted
-    // When cluster has heterogeneous container requests. (Please check test
-    // report: https://issues.apache.org/jira/secure/attachment/12796197/YARN-4390-test-results.pdf
-    //
-    // However, on the other hand, in some corner cases, especially for
-    // fragmented cluster. It could lead to preemption cannot kick in in some
-    // cases. Please see YARN-5731.
-    //
-    // So to solve the problem, we will include reserved when surgical preemption
-    // for reserved container, which reverts behavior when YARN-4390 is disabled.
     candidatesSelectionPolicies.add(new FifoCandidatesSelector(this,
-        !selectCandidatesForResevedContainers));
+        additionalPreemptionBasedOnReservedResource));
 
     // Do we need to specially consider intra queue
     boolean isIntraQueuePreemptionEnabled = csConfig.getBoolean(

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/main/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/CapacitySchedulerConfiguration.java

@@ -1205,6 +1205,33 @@ public class CapacitySchedulerConfiguration extends ReservationSchedulerConfigur
   public static final float DEFAULT_PREEMPTION_NATURAL_TERMINATION_FACTOR =
       0.2f;
 
+  /**
+   * By default, reserved resource will be excluded while balancing capacities
+   * of queues.
+   *
+   * Why doing this? In YARN-4390, we added preemption-based-on-reserved-container
+   * Support. To reduce unnecessary preemption for large containers. We will
+   * not include reserved resources while calculating ideal-allocation in
+   * FifoCandidatesSelector.
+   *
+   * Changes in YARN-4390 will significantly reduce number of containers preempted
+   * When cluster has heterogeneous container requests. (Please check test
+   * report: https://issues.apache.org/jira/secure/attachment/12796197/YARN-4390-test-results.pdf
+   *
+   * However, on the other hand, in some corner cases, especially for
+   * fragmented cluster. It could lead to preemption cannot kick in in some
+   * cases. Please see YARN-5731.
+   *
+   * So to solve the problem, make this change to be configurable, and please
+   * note that it is an experimental option.
+   */
+  public static final String
+      ADDITIONAL_RESOURCE_BALANCE_BASED_ON_RESERVED_CONTAINERS =
+      PREEMPTION_CONFIG_PREFIX
+          + "additional_res_balance_based_on_reserved_containers";
+  public static final boolean
+      DEFAULT_ADDITIONAL_RESOURCE_BALANCE_BASED_ON_RESERVED_CONTAINERS = false;
+
   /**
    * When calculating which containers to be preempted, we will try to preempt
    * containers for reserved containers first. By default is false.

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/scheduler/capacity/TestCapacitySchedulerSurgicalPreemption.java

@@ -813,9 +813,11 @@ public class TestCapacitySchedulerSurgicalPreemption
 
   @Test(timeout = 60000)
   public void testPreemptionForFragmentatedCluster() throws Exception {
+    // Set additional_balance_queue_based_on_reserved_res to true to get
+    // additional preemptions.
     conf.setBoolean(
-        CapacitySchedulerConfiguration.PREEMPTION_SELECT_CANDIDATES_FOR_RESERVED_CONTAINERS,
-        false);
+        CapacitySchedulerConfiguration.ADDITIONAL_RESOURCE_BALANCE_BASED_ON_RESERVED_CONTAINERS,
+        true);
 
     /**
      * Two queues, a/b, each of them are 50/50