--- a/src/hotspot/share/runtime/safepoint.cpp	Tue Sep 25 14:23:37 2018 +0200
+++ b/src/hotspot/share/runtime/safepoint.cpp	Mon Sep 24 18:44:39 2018 +0200
@@ -598,7 +598,8 @@
 
 public:
   ParallelSPCleanupThreadClosure(DeflateMonitorCounters* counters) :
-    _nmethod_cl(NMethodSweeper::prepare_mark_active_nmethods()), _counters(counters) {}
+    _nmethod_cl(UseCodeAging ? NMethodSweeper::prepare_reset_hotness_counters() : NULL),
+    _counters(counters) {}
 
   void do_thread(Thread* thread) {
     ObjectSynchronizer::deflate_thread_local_monitors(thread, _counters);

--- a/src/hotspot/share/runtime/sweeper.cpp	Tue Sep 25 14:23:37 2018 +0200
+++ b/src/hotspot/share/runtime/sweeper.cpp	Mon Sep 24 18:44:39 2018 +0200
@@ -28,15 +28,19 @@
 #include "code/icBuffer.hpp"
 #include "code/nmethod.hpp"
 #include "compiler/compileBroker.hpp"
+#include "gc/shared/collectedHeap.hpp"
+#include "gc/shared/workgroup.hpp"
 #include "jfr/jfrEvents.hpp"
 #include "logging/log.hpp"
 #include "logging/logStream.hpp"
 #include "memory/allocation.inline.hpp"
 #include "memory/resourceArea.hpp"
+#include "memory/universe.hpp"
 #include "oops/method.hpp"
 #include "runtime/atomic.hpp"
 #include "runtime/compilationPolicy.hpp"
 #include "runtime/interfaceSupport.inline.hpp"
+#include "runtime/handshake.hpp"
 #include "runtime/mutexLocker.hpp"
 #include "runtime/orderAccess.hpp"
 #include "runtime/os.hpp"
@@ -197,6 +201,38 @@
   return _current.end();
 }
 
+class NMethodMarkingThreadClosure : public ThreadClosure {
+private:
+  CodeBlobClosure* _cl;
+public:
+  NMethodMarkingThreadClosure(CodeBlobClosure* cl) : _cl(cl) {}
+  void do_thread(Thread* thread) {
+    if (thread->is_Java_thread() && ! thread->is_Code_cache_sweeper_thread()) {
+      JavaThread* jt = (JavaThread*) thread;
+      jt->nmethods_do(_cl);
+    }
+  }
+};
+
+class NMethodMarkingTask : public AbstractGangTask {
+private:
+  NMethodMarkingThreadClosure* _cl;
+public:
+  NMethodMarkingTask(NMethodMarkingThreadClosure* cl) :
+    AbstractGangTask("Parallel NMethod Marking"),
+    _cl(cl) {
+    Threads::change_thread_claim_parity();
+  }
+
+  ~NMethodMarkingTask() {
+    Threads::assert_all_threads_claimed();
+  }
+
+  void work(uint worker_id) {
+    Threads::possibly_parallel_threads_do(true, _cl);
+  }
+};
+
 /**
   * Scans the stacks of all Java threads and marks activations of not-entrant methods.
   * No need to synchronize access, since 'mark_active_nmethods' is always executed at a
@@ -205,12 +241,56 @@
 void NMethodSweeper::mark_active_nmethods() {
   CodeBlobClosure* cl = prepare_mark_active_nmethods();
   if (cl != NULL) {
-    Threads::nmethods_do(cl);
+    WorkGang* workers = Universe::heap()->get_safepoint_workers();
+    if (workers != NULL) {
+      NMethodMarkingThreadClosure tcl(cl);
+      NMethodMarkingTask task(&tcl);
+      workers->run_task(&task);
+    } else {
+      Threads::nmethods_do(cl);
+    }
   }
 }
 
 CodeBlobClosure* NMethodSweeper::prepare_mark_active_nmethods() {
+#ifdef ASSERT
+  if (ThreadLocalHandshakes) {
+    assert(Thread::current()->is_Code_cache_sweeper_thread(), "must be executed under CodeCache_lock and in sweeper thread");
+    assert_lock_strong(CodeCache_lock);
+  } else {
+    assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
+  }
+#endif
+
+  // If we do not want to reclaim not-entrant or zombie methods there is no need
+  // to scan stacks
+  if (!MethodFlushing) {
+    return NULL;
+  }
+
+  // Increase time so that we can estimate when to invoke the sweeper again.
+  _time_counter++;
+
+  // Check for restart
+  assert(_current.method() == NULL, "should only happen between sweeper cycles");
+  assert(wait_for_stack_scanning(), "should only happen between sweeper cycles");
+
+  _seen = 0;
+  _current = CompiledMethodIterator();
+  // Initialize to first nmethod
+  _current.next();
+  _traversals += 1;
+  _total_time_this_sweep = Tickspan();
+
+  if (PrintMethodFlushing) {
+    tty->print_cr("### Sweep: stack traversal %ld", _traversals);
+  }
+  return &mark_activation_closure;
+}
+
+CodeBlobClosure* NMethodSweeper::prepare_reset_hotness_counters() {
   assert(SafepointSynchronize::is_at_safepoint(), "must be executed at a safepoint");
+
   // If we do not want to reclaim not-entrant or zombie methods there is no need
   // to scan stacks
   if (!MethodFlushing) {
@@ -231,24 +311,7 @@
     }
   }
 
-  if (wait_for_stack_scanning()) {
-    _seen = 0;
-    _current = CompiledMethodIterator();
-    // Initialize to first nmethod
-    _current.next();
-    _traversals += 1;
-    _total_time_this_sweep = Tickspan();
-
-    if (PrintMethodFlushing) {
-      tty->print_cr("### Sweep: stack traversal %ld", _traversals);
-    }
-    return &mark_activation_closure;
-
-  } else {
-    // Only set hotness counter
-    return &set_hotness_closure;
-  }
-
+  return &set_hotness_closure;
 }
 
 /**
@@ -258,8 +321,20 @@
 void NMethodSweeper::do_stack_scanning() {
   assert(!CodeCache_lock->owned_by_self(), "just checking");
   if (wait_for_stack_scanning()) {
-    VM_MarkActiveNMethods op;
-    VMThread::execute(&op);
+    if (ThreadLocalHandshakes) {
+      CodeBlobClosure* code_cl;
+      {
+        MutexLockerEx ccl(CodeCache_lock, Mutex::_no_safepoint_check_flag);
+        code_cl = prepare_mark_active_nmethods();
+      }
+      if (code_cl != NULL) {
+        NMethodMarkingThreadClosure tcl(code_cl);
+        Handshake::execute(&tcl);
+      }
+    } else {
+      VM_MarkActiveNMethods op;
+      VMThread::execute(&op);
+    }
     _should_sweep = true;
   }
 }

--- a/src/hotspot/share/runtime/sweeper.hpp	Tue Sep 25 14:23:37 2018 +0200
+++ b/src/hotspot/share/runtime/sweeper.hpp	Mon Sep 24 18:44:39 2018 +0200
@@ -117,6 +117,7 @@
 
   static void mark_active_nmethods();      // Invoked at the end of each safepoint
   static CodeBlobClosure* prepare_mark_active_nmethods();
+  static CodeBlobClosure* prepare_reset_hotness_counters();
   static void sweeper_loop();
   static void notify(int code_blob_type);  // Possibly start the sweeper thread.
   static void force_sweep();