6976350: G1: deal with fragmentation while copying objects during GC Summary: Create G1ParGCAllocBufferContainer to contain two buffers instead of previously using one buffer, in order to hold the first priority buffer longer. Thus, when some large objects hits the value of free space left in the first priority buffer it has an alternative to fit in the second priority buffer while the first priority buffer is given more chances to try allocating smaller objects. Overall, it will improve heap space efficiency. Reviewed-by: johnc, jmasa, brutisso Contributed-by: tamao <tao.mao@oracle.com>

--- a/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Tue May 28 09:32:06 2013 +0200
+++ b/src/share/vm/gc_implementation/shared/parGCAllocBuffer.hpp	Mon Jun 03 14:37:13 2013 -0700
@@ -158,7 +158,7 @@
   // Fills in the unallocated portion of the buffer with a garbage object.
   // If "end_of_gc" is TRUE, is after the last use in the GC.  IF "retain"
   // is true, attempt to re-use the unused portion in the next GC.
-  void retire(bool end_of_gc, bool retain);
+  virtual void retire(bool end_of_gc, bool retain);
 
   void print() PRODUCT_RETURN;
 };