8048085: Aborting marking just before remark results in useless additional...

8048085: Aborting marking just before remark results in useless additional clearing of the next mark bitmap
Summary: Skip clearing the next bitmap if we just recently aborted since the full GC already clears this bitmap.
Reviewed-by: brutisso

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

@@ -890,6 +890,10 @@ 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) {
@@ -3362,7 +3366,8 @@ 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

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

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

@@ -275,9 +275,13 @@ 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");
       }
     }