8280705: Parallel: Full gc mark stack draining should prefer to make work available to other threads

Reviewed-by: ayang, mli

src/hotspot/share/gc/parallel/psCompactionManager.cpp

@@ -113,12 +113,24 @@ ParCompactionManager::gc_thread_compaction_manager(uint index) {
   return _manager_array[index];
 }
 
+bool ParCompactionManager::transfer_from_overflow_stack(ObjArrayTask& task) {
+  while (_objarray_stack.pop_overflow(task)) {
+    if (!_objarray_stack.try_push_to_taskqueue(task)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 void ParCompactionManager::follow_marking_stacks() {
   do {
-    // Drain the overflow stack first, to allow stealing from the marking stack.
+    // First, try to move tasks from the overflow stack into the shared buffer, so
+    // that other threads can steal. Otherwise process the overflow stack first.
     oop obj;
     while (marking_stack()->pop_overflow(obj)) {
-      follow_contents(obj);
+      if (!marking_stack()->try_push_to_taskqueue(obj)) {
+        follow_contents(obj);
+      }
     }
     while (marking_stack()->pop_local(obj)) {
       follow_contents(obj);
@@ -126,7 +138,7 @@ void ParCompactionManager::follow_marking_stacks() {
 
     // Process ObjArrays one at a time to avoid marking stack bloat.
     ObjArrayTask task;
-    if (_objarray_stack.pop_overflow(task) || _objarray_stack.pop_local(task)) {
+    if (transfer_from_overflow_stack(task) || _objarray_stack.pop_local(task)) {
       follow_array((objArrayOop)task.obj(), task.index());
     }
   } while (!marking_stacks_empty());

src/hotspot/share/gc/parallel/psCompactionManager.hpp

@@ -97,6 +97,7 @@ class ParCompactionManager : public CHeapObj<mtGC> {
 
   static void initialize(ParMarkBitMap* mbm);
 
+  bool transfer_from_overflow_stack(ObjArrayTask& task);
  protected:
   // Array of task queues.  Needed by the task terminator.
   static RegionTaskQueueSet* region_task_queues()      { return _region_task_queues; }

src/hotspot/share/gc/parallel/psParallelCompact.cpp

@@ -1984,17 +1984,15 @@ void steal_marking_work(TaskTerminator& terminator, uint worker_id) {
   ParCompactionManager* cm =
     ParCompactionManager::gc_thread_compaction_manager(worker_id);
 
-  oop obj = NULL;
-  ObjArrayTask task;
   do {
-    while (ParCompactionManager::steal_objarray(worker_id,  task)) {
+    oop obj = NULL;
+    ObjArrayTask task;
+    if (ParCompactionManager::steal_objarray(worker_id,  task)) {
       cm->follow_array((objArrayOop)task.obj(), task.index());
-      cm->follow_marking_stacks();
-    }
-    while (ParCompactionManager::steal(worker_id, obj)) {
+    } else if (ParCompactionManager::steal(worker_id, obj)) {
       cm->follow_contents(obj);
-      cm->follow_marking_stacks();
     }
+    cm->follow_marking_stacks();
   } while (!terminator.offer_termination());
 }