YARN-7469. Capacity Scheduler Intra-queue preemption: User can starve if newest app is exactly at user limit. Contributed by Eric Payne.

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

@@ -203,6 +203,12 @@ public class FifoIntraQueuePreemptionPlugin
       Resources.subtractFromNonNegative(preemtableFromApp, tmpApp.selected);
       Resources.subtractFromNonNegative(preemtableFromApp, tmpApp.getAMUsed());
 
+      if (context.getIntraQueuePreemptionOrderPolicy()
+            .equals(IntraQueuePreemptionOrderPolicy.USERLIMIT_FIRST)) {
+        Resources.subtractFromNonNegative(preemtableFromApp,
+          tmpApp.getFiCaSchedulerApp().getCSLeafQueue().getMinimumAllocation());
+      }
+
       // Calculate toBePreempted from apps as follows:
       // app.preemptable = min(max(app.used - app.selected - app.ideal, 0),
       // intra_q_preemptable)

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/ProportionalCapacityPreemptionPolicyMockFramework.java

@@ -358,6 +358,9 @@ public class ProportionalCapacityPreemptionPolicyMockFramework {
       queue = (LeafQueue) nameToCSQueues.get(queueName);
       queue.getApplications().add(app);
       queue.getAllApplications().add(app);
+      when(queue.getMinimumAllocation())
+      .thenReturn(Resource.newInstance(1,1));
+      when(app.getCSLeafQueue()).thenReturn(queue);
 
       HashSet<String> users = userMap.get(queueName);
       if (null == users) {

hadoop-yarn-project/hadoop-yarn/hadoop-yarn-server/hadoop-yarn-server-resourcemanager/src/test/java/org/apache/hadoop/yarn/server/resourcemanager/monitor/capacity/TestProportionalCapacityPreemptionPolicyIntraQueueUserLimit.java

@@ -896,4 +896,39 @@ public class TestProportionalCapacityPreemptionPolicyIntraQueueUserLimit
         new TestProportionalCapacityPreemptionPolicy.IsPreemptionRequestFor(
             getAppAttemptId(1))));
   }
+
+  @Test
+  public void testSimpleIntraQueuePreemptionOneUserUnderOneUserAtOneUserAbove()
+      throws IOException {
+    conf.setFloat(CapacitySchedulerConfiguration.
+        INTRAQUEUE_PREEMPTION_MAX_ALLOWABLE_LIMIT,
+        (float) 0.5);
+
+    String labelsConfig = "=100,true;";
+    String nodesConfig = // n1 has no label
+        "n1= res=100";
+    String queuesConfig =
+        // guaranteed,max,used,pending,reserved
+        "root(=[100 100 100 1 0]);" + // root
+            "-a(=[100 100 100 1 0])"; // a
+
+    String appsConfig =
+    // queueName\t(priority,resource,host,expression,#repeat,reserved,pending)
+        "a\t" // app1 in a
+            + "(1,1,n1,,65,false,0,user1);" +
+            "a\t" // app2 in a
+            + "(1,1,n1,,35,false,0,user2);" +
+            "a\t" // app3 in a
+            + "(1,1,n1,,0,false,1,user3)"
+            ;
+
+    buildEnv(labelsConfig, nodesConfig, queuesConfig, appsConfig);
+    policy.editSchedule();
+
+    // app2 is right at its user limit and app1 needs one resource. Should
+    // preempt 1 container.
+    verify(mDisp, times(1)).handle(argThat(
+        new TestProportionalCapacityPreemptionPolicy.IsPreemptionRequestFor(
+            getAppAttemptId(1))));
+  }
 }