--- old/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.cpp	2010-03-10 14:49:38.000000000 -0800
+++ new/src/share/vm/gc_implementation/parallelScavenge/psYoungGen.cpp	2010-03-10 14:49:38.000000000 -0800
@@ -163,6 +163,9 @@
   set_space_boundaries(eden_size, survivor_size);
   space_invariants();
 
+  _init_survivor_size = survivor_size;
+  _init_eden_size = eden_size;
+
   if (UsePerfData) {
     _eden_counters->update_capacity();
     _from_counters->update_capacity();
@@ -949,3 +952,76 @@
   to_space()->set_top_for_allocations();
 }
 #endif
+
+void PSYoungGen::try_to_shrink_by(size_t shrink_bytes) {
+  size_t free_bytes = capacity_in_bytes() - used_in_bytes();
+  if (free_bytes == 0) {
+    // cannot shrink
+    return;
+  }
+  size_t eden_free_bytes = eden_space()->capacity_in_bytes() - eden_space()->used_in_bytes();
+  size_t survivor_free_bytes = from_space()->capacity_in_bytes() - from_space()->used_in_bytes();
+  size_t eden_shrink_bytes =
+      (size_t) (shrink_bytes * ((double) eden_free_bytes / free_bytes));
+  size_t survivor_shrink_bytes =
+      (size_t) (shrink_bytes * ((double) survivor_free_bytes / free_bytes));
+
+  // Don't shrink unless it's significant
+  if (eden_shrink_bytes < MinHeapDeltaBytes) {
+    eden_shrink_bytes = 0;
+  }
+  if (survivor_shrink_bytes < MinHeapDeltaBytes) {
+    survivor_shrink_bytes = 0;
+  }
+
+  if (eden_shrink_bytes == 0 && survivor_shrink_bytes == 0) {
+    return; // no change, so return now
+  }
+
+  size_t eden_desired_capacity =
+      eden_space()->capacity_in_bytes() - eden_shrink_bytes;
+  eden_desired_capacity = MAX2(eden_desired_capacity, _init_eden_size);
+  assert(eden_space()->used_in_bytes() <= eden_desired_capacity, "sanity check");
+  eden_desired_capacity = align_size_down(eden_desired_capacity,
+                                          virtual_space()->alignment());
+
+  size_t survivor_desired_capacity =
+      from_space()->capacity_in_bytes() - survivor_shrink_bytes;
+  survivor_desired_capacity = MAX2(survivor_desired_capacity, _init_survivor_size);
+  assert(from_space()->used_in_bytes() <= survivor_desired_capacity, "sanity check");
+  survivor_desired_capacity = align_size_down(survivor_desired_capacity,
+                                              virtual_space()->alignment());
+
+  if (eden_desired_capacity == eden_space()->capacity_in_bytes()
+      && survivor_desired_capacity == from_space()->capacity_in_bytes()) {
+    return; // no change, so return now
+  }
+
+  if (PrintGC) {
+    gclog_or_tty->print_cr(" Resizing young gen. shrink_bytes=%d,%d",
+                           eden_shrink_bytes, survivor_shrink_bytes);
+    gclog_or_tty->print("BEFORE: Young Gen: ");
+    gclog_or_tty->print("eden capacity : " SIZE_FORMAT ", ",
+                        eden_space()->capacity_in_bytes());
+    gclog_or_tty->print("eden used : " SIZE_FORMAT ", " ,
+                        eden_space()->used_in_bytes());
+    gclog_or_tty->print("survivor capacity : " SIZE_FORMAT ", ",
+                        from_space()->capacity_in_bytes());
+    gclog_or_tty->print_cr("survivor used : " SIZE_FORMAT ", " ,
+                           from_space()->used_in_bytes());
+  }
+
+  resize(eden_desired_capacity, survivor_desired_capacity);
+
+  if (PrintGC) {
+    gclog_or_tty->print("AFTER: Young Gen: ");
+    gclog_or_tty->print("eden capacity : " SIZE_FORMAT ", ",
+                        eden_space()->capacity_in_bytes());
+    gclog_or_tty->print("eden used : " SIZE_FORMAT ", " ,
+                        eden_space()->used_in_bytes());
+    gclog_or_tty->print("survivor capacity : " SIZE_FORMAT ", ",
+                        from_space()->capacity_in_bytes());
+    gclog_or_tty->print_cr("survivor used : " SIZE_FORMAT ", " ,
+                           from_space()->used_in_bytes());
+  }
+}