8048556: Unnecessary GCLocker-initiated young GCs

Summary: Fixed recognition of unnecessary GCLocker collections.
Reviewed-by: pliden, tschatzl
Contributed-by: johnc@azul.com

src/share/vm/gc_implementation/g1/g1CollectedHeap.cpp

@@ -2520,6 +2520,12 @@ void G1CollectedHeap::collect(GCCause::Cause cause) {
           }
         }
       }
+    } else if (GC_locker::should_discard(cause, gc_count_before)) {
+      // Return to be consistent with VMOp failure due to another
+      // collection slipping in after our gc_count but before our
+      // request is processed.  _gc_locker collections upgraded by
+      // GCLockerInvokesConcurrent are handled above and never discarded.
+      return;
     } else {
       if (cause == GCCause::_gc_locker || cause == GCCause::_wb_young_gc
           DEBUG_ONLY(|| cause == GCCause::_scavenge_alot)) {

src/share/vm/gc_implementation/parallelScavenge/parallelScavengeHeap.cpp

@@ -530,6 +530,10 @@ void ParallelScavengeHeap::collect(GCCause::Cause cause) {
     full_gc_count = Universe::heap()->total_full_collections();
   }
 
+  if (GC_locker::should_discard(cause, gc_count)) {
+    return;
+  }
+
   VM_ParallelGCSystemGC op(gc_count, full_gc_count, cause);
   VMThread::execute(&op);
 }

src/share/vm/gc_implementation/parallelScavenge/vmPSOperations.cpp

@@ -52,11 +52,16 @@ void VM_ParallelGCFailedAllocation::doit() {
   }
 }
 
+static bool is_cause_full(GCCause::Cause cause) {
+  return (cause != GCCause::_gc_locker) && (cause != GCCause::_wb_young_gc)
+         DEBUG_ONLY(&& (cause != GCCause::_scavenge_alot));
+}
+
 // Only used for System.gc() calls
 VM_ParallelGCSystemGC::VM_ParallelGCSystemGC(uint gc_count,
                                              uint full_gc_count,
                                              GCCause::Cause gc_cause) :
-  VM_GC_Operation(gc_count, gc_cause, full_gc_count, true /* full */)
+  VM_GC_Operation(gc_count, gc_cause, full_gc_count, is_cause_full(gc_cause))
 {
 }
 
@@ -68,8 +73,7 @@ void VM_ParallelGCSystemGC::doit() {
     "must be a ParallelScavengeHeap");
 
   GCCauseSetter gccs(heap, _gc_cause);
-  if (_gc_cause == GCCause::_gc_locker || _gc_cause == GCCause::_wb_young_gc
-      DEBUG_ONLY(|| _gc_cause == GCCause::_scavenge_alot)) {
+  if (!_full) {
     // If (and only if) the scavenge fails, this will invoke a full gc.
     heap->invoke_scavenge();
   } else {

src/share/vm/gc_implementation/shared/vmGCOperations.cpp

@@ -201,6 +201,19 @@ void VM_GenCollectForAllocation::doit() {
   }
 }
 
+static bool is_full_gc(int max_level) {
+  // Return true if max_level is all generations
+  return (max_level == (GenCollectedHeap::heap()->n_gens() - 1));
+}
+
+VM_GenCollectFull::VM_GenCollectFull(uint gc_count_before,
+                                     uint full_gc_count_before,
+                                     GCCause::Cause gc_cause,
+                                     int max_level) :
+  VM_GC_Operation(gc_count_before, gc_cause, full_gc_count_before,
+                  is_full_gc(max_level) /* full */),
+  _max_level(max_level) { }
+
 void VM_GenCollectFull::doit() {
   SvcGCMarker sgcm(SvcGCMarker::FULL);
 

src/share/vm/gc_implementation/shared/vmGCOperations.hpp

@@ -201,9 +201,7 @@ class VM_GenCollectFull: public VM_GC_Operation {
   VM_GenCollectFull(uint gc_count_before,
                     uint full_gc_count_before,
                     GCCause::Cause gc_cause,
-                    int max_level)
-    : VM_GC_Operation(gc_count_before, gc_cause, full_gc_count_before, true /* full */),
-      _max_level(max_level) { }
+                    int max_level);
   ~VM_GenCollectFull() {}
   virtual VMOp_Type type() const { return VMOp_GenCollectFull; }
   virtual void doit();

src/share/vm/memory/gcLocker.cpp

@@ -31,6 +31,7 @@
 volatile jint GC_locker::_jni_lock_count = 0;
 volatile bool GC_locker::_needs_gc       = false;
 volatile bool GC_locker::_doing_gc       = false;
+unsigned int  GC_locker::_total_collections = 0;
 
 #ifdef ASSERT
 volatile jint GC_locker::_debug_jni_lock_count = 0;
@@ -94,6 +95,11 @@ void GC_locker::stall_until_clear() {
   }
 }
 
+bool GC_locker::should_discard(GCCause::Cause cause, uint total_collections) {
+  return (cause == GCCause::_gc_locker) &&
+         (_total_collections != total_collections);
+}
+
 void GC_locker::jni_lock(JavaThread* thread) {
   assert(!thread->in_critical(), "shouldn't currently be in a critical region");
   MutexLocker mu(JNICritical_lock);
@@ -117,7 +123,13 @@ void GC_locker::jni_unlock(JavaThread* thread) {
   decrement_debug_jni_lock_count();
   thread->exit_critical();
   if (needs_gc() && !is_active_internal()) {
-    // We're the last thread out. Cause a GC to occur.
+    // We're the last thread out. Request a GC.
+    // Capture the current total collections, to allow detection of
+    // other collections that make this one unnecessary.  The value of
+    // total_collections() is only changed at a safepoint, so there
+    // must not be a safepoint between the lock becoming inactive and
+    // getting the count, else there may be unnecessary GCLocker GCs.
+    _total_collections = Universe::heap()->total_collections();
     _doing_gc = true;
     {
       // Must give up the lock while at a safepoint

src/share/vm/memory/gcLocker.hpp

@@ -26,6 +26,7 @@
 #define SHARE_VM_MEMORY_GCLOCKER_HPP
 
 #include "gc_interface/collectedHeap.hpp"
+#include "gc_interface/gcCause.hpp"
 #include "memory/genCollectedHeap.hpp"
 #include "memory/universe.hpp"
 #include "oops/oop.hpp"
@@ -57,6 +58,7 @@ class GC_locker: public AllStatic {
   static volatile bool _needs_gc;        // heap is filling, we need a GC
                                          // note: bool is typedef'd as jint
   static volatile bool _doing_gc;        // unlock_critical() is doing a GC
+  static uint _total_collections;        // value for _gc_locker collection
 
 #ifdef ASSERT
   // This lock count is updated for all operations and is used to
@@ -116,6 +118,12 @@ class GC_locker: public AllStatic {
   // Sets _needs_gc if is_active() is true. Returns is_active().
   static bool check_active_before_gc();
 
+  // Return true if the designated collection is a GCLocker request
+  // that should be discarded.  Returns true if cause == GCCause::_gc_locker
+  // and the given total collection value indicates a collection has been
+  // done since the GCLocker request was made.
+  static bool should_discard(GCCause::Cause cause, uint total_collections);
+
   // Stalls the caller (who should not be in a jni critical section)
   // until needs_gc() clears. Note however that needs_gc() may be
   // set at a subsequent safepoint and/or cleared under the

src/share/vm/memory/genCollectedHeap.cpp

@@ -796,8 +796,11 @@ void GenCollectedHeap::collect(GCCause::Cause cause) {
 #else  // INCLUDE_ALL_GCS
     ShouldNotReachHere();
 #endif // INCLUDE_ALL_GCS
-  } else if (cause == GCCause::_wb_young_gc) {
-    // minor collection for WhiteBox API
+  } else if ((cause == GCCause::_wb_young_gc) ||
+             (cause == GCCause::_gc_locker)) {
+    // minor collection for WhiteBox or GCLocker.
+    // _gc_locker collections upgraded by GCLockerInvokesConcurrent
+    // are handled above and never discarded.
     collect(cause, 0);
   } else {
 #ifdef ASSERT
@@ -835,6 +838,11 @@ void GenCollectedHeap::collect_locked(GCCause::Cause cause, int max_level) {
   // Read the GC count while holding the Heap_lock
   unsigned int gc_count_before      = total_collections();
   unsigned int full_gc_count_before = total_full_collections();
+
+  if (GC_locker::should_discard(cause, gc_count_before)) {
+    return;
+  }
+
   {
     MutexUnlocker mu(Heap_lock);  // give up heap lock, execute gets it back
     VM_GenCollectFull op(gc_count_before, full_gc_count_before,
@@ -887,24 +895,16 @@ void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs) {
 
 void GenCollectedHeap::do_full_collection(bool clear_all_soft_refs,
                                           int max_level) {
-  int local_max_level;
-  if (!incremental_collection_will_fail(false /* don't consult_young */) &&
-      gc_cause() == GCCause::_gc_locker) {
-    local_max_level = 0;
-  } else {
-    local_max_level = max_level;
-  }
 
   do_collection(true                 /* full */,
                 clear_all_soft_refs  /* clear_all_soft_refs */,
                 0                    /* size */,
                 false                /* is_tlab */,
-                local_max_level      /* max_level */);
+                max_level            /* max_level */);
   // Hack XXX FIX ME !!!
   // A scavenge may not have been attempted, or may have
   // been attempted and failed, because the old gen was too full
-  if (local_max_level == 0 && gc_cause() == GCCause::_gc_locker &&
-      incremental_collection_will_fail(false /* don't consult_young */)) {
+  if (gc_cause() == GCCause::_gc_locker && incremental_collection_failed()) {
     if (PrintGCDetails) {
       gclog_or_tty->print_cr("GC locker: Trying a full collection "
                              "because scavenge failed");

test/gc/stress/gclocker/TestExcessGCLockerCollections.java

+/*
+ * Copyright (c) 2019, Oracle and/or its affiliates. All rights reserved.
+ * 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.
+ *
+ * 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 gc.stress.gclocker;
+
+// Based on Kim Barrett;s test for JDK-8048556
+
+/*
+ * @test TestExcessGCLockerCollections
+ * @key gc
+ * @bug 8048556
+ * @summary Check for GC Locker initiated GCs that immediately follow another
+ * GC and so have very little needing to be collected.
+ * @library /testlibrary
+ * @run driver/timeout=1000 gc.stress.gclocker.TestExcessGCLockerCollections 300 4 2
+ */
+
+import java.util.HashMap;
+import java.util.Map;
+
+import java.util.zip.Deflater;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+
+import javax.management.MBeanServer;
+import javax.management.Notification;
+import javax.management.NotificationListener;
+import javax.management.openmbean.CompositeData;
+import java.lang.management.ManagementFactory;
+import java.lang.management.GarbageCollectorMXBean;
+import java.lang.management.MemoryUsage;
+import java.util.List;
+import com.sun.management.GarbageCollectionNotificationInfo;
+import com.sun.management.GcInfo;
+
+import com.oracle.java.testlibrary.Asserts;
+import com.oracle.java.testlibrary.ProcessTools;
+import com.oracle.java.testlibrary.OutputAnalyzer;
+
+class TestExcessGCLockerCollectionsStringConstants {
+    // Some constant strings used in both GC logging and error detection
+    static public final String GCLOCKER_CAUSE = "GCLocker Initiated GC";
+    static public final String USED_TOO_LOW = "TOO LOW";
+    static public final String USED_OK = "OK";
+}
+
+class TestExcessGCLockerCollectionsAux {
+    static private final int LARGE_MAP_SIZE = 64 * 1024;
+
+    static private final int MAP_ARRAY_LENGTH = 4;
+    static private final int MAP_SIZE = 1024;
+
+    static private final int BYTE_ARRAY_LENGTH = 128 * 1024;
+
+    static private void println(String str) { System.out.println(str); }
+    static private void println()           { System.out.println();    }
+
+    static private volatile boolean keepRunning = true;
+
+    static Map<Integer,String> populateMap(int size) {
+        Map<Integer,String> map = new HashMap<Integer,String>();
+        for (int i = 0; i < size; i += 1) {
+            Integer keyInt = Integer.valueOf(i);
+            String valStr = "value is [" + i + "]";
+            map.put(keyInt,valStr);
+        }
+        return map;
+    }
+
+    static private class AllocatingWorker implements Runnable {
+        private final Object[] array = new Object[MAP_ARRAY_LENGTH];
+        private int arrayIndex = 0;
+
+        private void doStep() {
+            Map<Integer,String> map = populateMap(MAP_SIZE);
+            array[arrayIndex] = map;
+            arrayIndex = (arrayIndex + 1) % MAP_ARRAY_LENGTH;
+        }
+
+        public void run() {
+            while (keepRunning) {
+                doStep();
+            }
+        }
+    }
+
+    static private class JNICriticalWorker implements Runnable {
+        private int count;
+
+        private void doStep() {
+            byte[] inputArray = new byte[BYTE_ARRAY_LENGTH];
+            for (int i = 0; i < inputArray.length; i += 1) {
+                inputArray[i] = (byte) (count + i);
+            }
+
+            Deflater deflater = new Deflater();
+            deflater.setInput(inputArray);
+            deflater.finish();
+
+            byte[] outputArray = new byte[2 * inputArray.length];
+            deflater.deflate(outputArray);
+
+            count += 1;
+        }
+
+        public void run() {
+            while (keepRunning) {
+                doStep();
+            }
+        }
+    }
+
+    static class GCNotificationListener implements NotificationListener {
+        static private final double MIN_USED_PERCENT = 40.0;
+
+        static private final List<String> newGenPoolNames = Arrays.asList(
+                "G1 Eden Space",           // OpenJDK G1GC: -XX:+UseG1GC
+                "PS Eden Space",           // OpenJDK ParallelGC: -XX:+ParallelGC
+                "Par Eden Space",          // OpenJDK ConcMarkSweepGC: -XX:+ConcMarkSweepGC
+                "Eden Space"               // OpenJDK SerialGC: -XX:+UseSerialGC
+                                           // OpenJDK ConcMarkSweepGC: -XX:+ConcMarkSweepGC -XX:-UseParNewGC
+        );
+
+        @Override
+        public void handleNotification(Notification notification, Object handback) {
+            try {
+                if (notification.getType().equals(GarbageCollectionNotificationInfo.GARBAGE_COLLECTION_NOTIFICATION)) {
+                    GarbageCollectionNotificationInfo info =
+                            GarbageCollectionNotificationInfo.from((CompositeData) notification.getUserData());
+
+                    String gc_cause = info.getGcCause();
+
+                    if (gc_cause.equals(TestExcessGCLockerCollectionsStringConstants.GCLOCKER_CAUSE)) {
+                        Map<String, MemoryUsage> memory_before_gc = info.getGcInfo().getMemoryUsageBeforeGc();
+
+                        for (String newGenPoolName : newGenPoolNames) {
+                            MemoryUsage usage = memory_before_gc.get(newGenPoolName);
+                            if (usage == null) continue;
+
+                            double startTime = ((double) info.getGcInfo().getStartTime()) / 1000.0;
+                            long used = usage.getUsed();
+                            long committed = usage.getCommitted();
+                            long max = usage.getMax();
+                            double used_percent = (((double) used) / Math.max(committed, max)) * 100.0;
+
+                            System.out.printf("%6.3f: (%s) %d/%d/%d, %8.4f%% (%s)\n",
+                                              startTime, gc_cause, used, committed, max, used_percent,
+                                              ((used_percent < MIN_USED_PERCENT) ? TestExcessGCLockerCollectionsStringConstants.USED_TOO_LOW
+                                                                                 : TestExcessGCLockerCollectionsStringConstants.USED_OK));
+                        }
+                    }
+                }
+            } catch (RuntimeException ex) {
+                System.err.println("Exception during notification processing:" + ex);
+                ex.printStackTrace();
+            }
+        }
+
+        public static boolean register() {
+            try {
+                MBeanServer mbeanServer = ManagementFactory.getPlatformMBeanServer();
+
+                // Get the list of MX
+                List<GarbageCollectorMXBean> gc_mxbeans = ManagementFactory.getGarbageCollectorMXBeans();
+
+                // Create the notification listener
+                GCNotificationListener gcNotificationListener = new GCNotificationListener();
+
+                for (GarbageCollectorMXBean gcbean : gc_mxbeans) {
+                  // Add notification listener for the MXBean
+                  mbeanServer.addNotificationListener(gcbean.getObjectName(), gcNotificationListener, null, null);
+                }
+            } catch (Exception ex) {
+                System.err.println("Exception during mbean registration:" + ex);
+                ex.printStackTrace();
+                // We've failed to set up, terminate
+                return false;
+            }
+
+            return true;
+        }
+    }
+
+    static public Map<Integer,String> largeMap;
+
+    static public void main(String args[]) {
+        long durationSec = Long.parseLong(args[0]);
+        int allocThreadNum = Integer.parseInt(args[1]);
+        int jniCriticalThreadNum = Integer.parseInt(args[2]);
+
+        println("Running for " + durationSec + " secs");
+
+        if (!GCNotificationListener.register()) {
+          println("failed to register GC notification listener");
+          System.exit(-1);
+        }
+
+        largeMap = populateMap(LARGE_MAP_SIZE);
+
+        println("Starting " + allocThreadNum + " allocating threads");
+        for (int i = 0; i < allocThreadNum; i += 1) {
+            new Thread(new AllocatingWorker()).start();
+        }
+
+        println("Starting " + jniCriticalThreadNum + " jni critical threads");
+        for (int i = 0; i < jniCriticalThreadNum; i += 1) {
+            new Thread(new JNICriticalWorker()).start();
+        }
+
+        long durationMS = (long) (1000 * durationSec);
+        long start = System.currentTimeMillis();
+        long now = start;
+        long soFar = now - start;
+        while (soFar < durationMS) {
+            try {
+                Thread.sleep(durationMS - soFar);
+            } catch (Exception e) {
+            }
+            now = System.currentTimeMillis();
+            soFar = now - start;
+        }
+        println("Done.");
+        keepRunning = false;
+    }
+}
+
+public class TestExcessGCLockerCollections {
+    private static final String USED_OK_LINE =
+        "\\(" + TestExcessGCLockerCollectionsStringConstants.GCLOCKER_CAUSE + "\\)"
+              + " .* " +
+        "\\(" + TestExcessGCLockerCollectionsStringConstants.USED_OK + "\\)";
+    private static final String USED_TOO_LOW_LINE =
+        "\\(" + TestExcessGCLockerCollectionsStringConstants.GCLOCKER_CAUSE + "\\)"
+              + " .* " +
+        "\\(" + TestExcessGCLockerCollectionsStringConstants.USED_TOO_LOW + "\\)";
+
+    private static final String[] COMMON_OPTIONS = new String[] {
+        "-Xmx1G", "-Xms1G", "-Xmn256M" };
+
+    public static void main(String args[]) throws Exception {
+        if (args.length < 3) {
+            System.out.println("usage: TestExcessGCLockerCollections" +
+                               " <duration sec> <alloc threads>" +
+                               " <jni critical threads>");
+            throw new RuntimeException("Invalid arguments");
+        }
+
+        ArrayList<String> finalArgs = new ArrayList<String>();
+        finalArgs.addAll(Arrays.asList(COMMON_OPTIONS));
+        finalArgs.add(TestExcessGCLockerCollectionsAux.class.getName());
+        finalArgs.addAll(Arrays.asList(args));
+
+        // GC and other options obtained from test framework.
+        ProcessBuilder pb = ProcessTools.createJavaProcessBuilder(
+            true, finalArgs.toArray(new String[0]));
+        OutputAnalyzer output = new OutputAnalyzer(pb.start());
+        output.shouldHaveExitValue(0);
+        //System.out.println("------------- begin stdout ----------------");
+        //System.out.println(output.getStdout());
+        //System.out.println("------------- end stdout ----------------");
+        output.stdoutShouldMatch(USED_OK_LINE);
+        output.stdoutShouldNotMatch(USED_TOO_LOW_LINE);
+    }
+}