8181859: Monitor deflation is not checked in cleanup path

Reviewed-by: sspitsyn, dcubed, shade, cvarming

hotspot/src/share/vm/runtime/globals.hpp

@@ -1184,6 +1184,12 @@ public:
                                                                             \
   product(bool, MonitorInUseLists, true, "Track Monitors for Deflation")    \
                                                                             \
+  experimental(intx, MonitorUsedDeflationThreshold, 90,                     \
+                "Percentage of used monitors before triggering cleanup "    \
+                "safepoint which deflates monitors (0 is off). "            \
+                "The check is performed on GuaranteedSafepointInterval.")   \
+                range(0, 100)                                               \
+                                                                            \
   experimental(intx, SyncFlags, 0, "(Unsafe, Unstable) "                    \
                "Experimental Sync flags")                                   \
                                                                             \

hotspot/src/share/vm/runtime/safepoint.cpp

@@ -525,6 +525,8 @@ void SafepointSynchronize::end() {
 }
 
 bool SafepointSynchronize::is_cleanup_needed() {
+  // Need a safepoint if there are many monitors to deflate.
+  if (ObjectSynchronizer::is_cleanup_needed()) return true;
   // Need a safepoint if some inline cache buffers is non-empty
   if (!InlineCacheBuffer::is_empty()) return true;
   return false;

hotspot/src/share/vm/runtime/synchronizer.cpp

@@ -962,6 +962,21 @@ static inline ObjectMonitor* next(ObjectMonitor* block) {
   return block;
 }
 
+static bool monitors_used_above_threshold() {
+  if (gMonitorPopulation == 0) {
+    return false;
+  }
+  int monitors_used = gMonitorPopulation - gMonitorFreeCount;
+  int monitor_usage = (monitors_used * 100LL) / gMonitorPopulation;
+  return monitor_usage > MonitorUsedDeflationThreshold;
+}
+
+bool ObjectSynchronizer::is_cleanup_needed() {
+  if (MonitorUsedDeflationThreshold > 0) {
+    return monitors_used_above_threshold();
+  }
+  return false;
+}
 
 void ObjectSynchronizer::oops_do(OopClosure* f) {
   if (MonitorInUseLists) {

hotspot/src/share/vm/runtime/synchronizer.hpp

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 1998, 2016, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 1998, 2017, 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
@@ -135,6 +135,7 @@ class ObjectSynchronizer : AllStatic {
   static bool deflate_monitor(ObjectMonitor* mid, oop obj,
                               ObjectMonitor** freeHeadp,
                               ObjectMonitor** freeTailp);
+  static bool is_cleanup_needed();
   static void oops_do(OopClosure* f);
   // Process oops in thread local used monitors
   static void thread_local_used_oops_do(Thread* thread, OopClosure* f);