src/hotspot/share/gc/cms/compactibleFreeListSpace.cpp

@@ -370,10 +370,12 @@
     DEBUG_ONLY(
       _indexedFreeList[i].set_protecting_lock(_indexedFreeListParLocks[i]);
     )
   }
   _dictionary->set_par_lock(&_parDictionaryAllocLock);
+
+  _used_stable = 0;
 }
 
 // Like CompactibleSpace forward() but always calls cross_threshold() to
 // update the block offset table.  Removed initialize_threshold call because
 // CFLS does not use a block offset array for contiguous spaces.

@@ -575,10 +577,18 @@
 
 size_t CompactibleFreeListSpace::used() const {
   return capacity() - free();
 }
 
+size_t CompactibleFreeListSpace::used_stable() const {
+  return _used_stable;
+}
+
+void CompactibleFreeListSpace::recalculate_used_stable() {
+  _used_stable = used();
+}
+
 size_t CompactibleFreeListSpace::free() const {
   // "MT-safe, but not MT-precise"(TM), if you will: i.e.
   // if you do this while the structures are in flux you
   // may get an approximate answer only; for instance
   // because there is concurrent allocation either

@@ -1372,10 +1382,17 @@
     _bt.verify_not_unallocated(res, size);
     // mangle a just allocated object with a distinct pattern.
     debug_only(fc->mangleAllocated(size));
   }
 
+  // During GC we do not need to recalculate the stable used value for
+  // every allocation in old gen. It is done once at the end of GC instead
+  // for performance reasons.
+  if (!CMSHeap::heap()->is_gc_active()) {
+    recalculate_used_stable();
+  }
+
   return res;
 }
 
 HeapWord* CompactibleFreeListSpace::allocate_adaptive_freelists(size_t size) {
   assert_lock_strong(freelistLock());