8048085: Aborting marking just before remark results in useless additional clearing of the next mark bitmap

Skip clearing the next bitmap if we just recently aborted since the full GC already clears this bitmap.

Reviewed-by: brutisso

hotspot/src/share/vm/gc_implementation/g1/concurrentMark.cpp

@@ -891,6 +891,10 @@ void ConcurrentMark::clearNextBitmap() {
   guarantee(!g1h->mark_in_progress(), "invariant");
 }
 
+bool ConcurrentMark::nextMarkBitmapIsClear() {
+  return _nextMarkBitMap->getNextMarkedWordAddress(_heap_start, _heap_end) == _heap_end;
+}
+
 class NoteStartOfMarkHRClosure: public HeapRegionClosure {
 public:
   bool doHeapRegion(HeapRegion* r) {
@@ -3358,7 +3362,8 @@ void ConcurrentMark::print_stats() {
 
 // abandon current marking iteration due to a Full GC
 void ConcurrentMark::abort() {
-  // Clear all marks to force marking thread to do nothing
+  // Clear all marks in the next bitmap for the next marking cycle. This will allow us to skip the next
+  // concurrent bitmap clearing.
   _nextMarkBitMap->clearAll();
 
   // Note we cannot clear the previous marking bitmap here

hotspot/src/share/vm/gc_implementation/g1/concurrentMark.hpp

@@ -736,6 +736,9 @@ public:
   // Clear the next marking bitmap (will be called concurrently).
   void clearNextBitmap();
 
+  // Return whether the next mark bitmap has no marks set.
+  bool nextMarkBitmapIsClear();
+
   // These two do the work that needs to be done before and after the
   // initial root checkpoint. Since this checkpoint can be done at two
   // different points (i.e. an explicit pause or piggy-backed on a

hotspot/src/share/vm/gc_implementation/g1/concurrentMarkThread.cpp

@@ -277,9 +277,13 @@ void ConcurrentMarkThread::run() {
 
       // We now want to allow clearing of the marking bitmap to be
       // suspended by a collection pause.
-      {
+      // We may have aborted just before the remark. Do not bother clearing the
+      // bitmap then, as it has been done during mark abort.
+      if (!cm()->has_aborted()) {
         SuspendibleThreadSetJoiner sts;
         _cm->clearNextBitmap();
+      } else {
+        assert(!G1VerifyBitmaps || _cm->nextMarkBitmapIsClear(), "Next mark bitmap must be clear");
       }
     }