--- old/src/share/vm/gc/g1/g1CollectedHeap.cpp	2015-06-06 02:21:43.000000000 +0200
+++ new/src/share/vm/gc/g1/g1CollectedHeap.cpp	2015-06-06 02:21:43.000000000 +0200
@@ -4373,7 +4373,7 @@
         // We also need to mark copied objects.
         strong_root_cl = &scan_mark_root_cl;
         strong_cld_cl  = &scan_mark_cld_cl;
-        if (ClassUnloadingWithConcurrentMark) {
+        if (ClassUnloading && ClassUnloadingWithConcurrentMark) {
           weak_root_cl = &scan_mark_weak_root_cl;
           weak_cld_cl  = &scan_mark_weak_cld_cl;
           trace_metadata = true;
@@ -4706,12 +4706,14 @@
 public:
 
   void clean_klass(InstanceKlass* ik) {
-    ik->clean_implementors_list(_is_alive);
-    ik->clean_method_data(_is_alive);
-
-    // G1 specific cleanup work that has
-    // been moved here to be done in parallel.
-    ik->clean_dependent_nmethods();
+    if (ClassUnloading) {
+      ik->clean_implementors_list(_is_alive);
+      ik->clean_method_data(_is_alive);
+
+      // G1 specific cleanup work that has
+      // been moved here to be done in parallel.
+      ik->clean_dependent_nmethods();
+    }
   }
 
   void work() {
--- old/src/share/vm/gc/g1/g1MarkSweep.cpp	2015-06-06 02:21:44.000000000 +0200
+++ new/src/share/vm/gc/g1/g1MarkSweep.cpp	2015-06-06 02:21:44.000000000 +0200
@@ -151,14 +151,16 @@
   // This is the point where the entire marking should have completed.
   assert(GenMarkSweep::_marking_stack.is_empty(), "Marking should have completed");
 
-  // Unload classes and purge the SystemDictionary.
-  bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
+  if (ClassUnloading) {
+    // Unload classes and purge the SystemDictionary.
+    bool purged_class = SystemDictionary::do_unloading(&GenMarkSweep::is_alive);
 
-  // Unload nmethods.
-  CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
+    // Unload nmethods.
+    CodeCache::do_unloading(&GenMarkSweep::is_alive, purged_class);
 
-  // Prune dead klasses from subklass/sibling/implementor lists.
-  Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
+    // Prune dead klasses from subklass/sibling/implementor lists.
+    Klass::clean_weak_klass_links(&GenMarkSweep::is_alive);
+  }
 
   // Delete entries for dead interned string and clean up unreferenced symbols in symbol table.
   g1h->unlink_string_and_symbol_table(&GenMarkSweep::is_alive);
--- old/src/share/vm/gc/g1/g1RootProcessor.cpp	2015-06-06 02:21:44.000000000 +0200
+++ new/src/share/vm/gc/g1/g1RootProcessor.cpp	2015-06-06 02:21:44.000000000 +0200
@@ -90,7 +90,7 @@
 
 
 void G1RootProcessor::worker_has_discovered_all_strong_classes() {
-  assert(ClassUnloadingWithConcurrentMark, "Currently only needed when doing G1 Class Unloading");
+  assert(ClassUnloading && ClassUnloadingWithConcurrentMark, "Currently only needed when doing G1 Class Unloading");
 
   uint new_value = (uint)Atomic::add(1, &_n_workers_discovered_strong_classes);
   if (new_value == n_workers()) {
@@ -101,7 +101,7 @@
 }
 
 void G1RootProcessor::wait_until_all_strong_classes_discovered() {
-  assert(ClassUnloadingWithConcurrentMark, "Currently only needed when doing G1 Class Unloading");
+  assert(ClassUnloading && ClassUnloadingWithConcurrentMark, "Currently only needed when doing G1 Class Unloading");
 
   if ((uint)_n_workers_discovered_strong_classes != n_workers()) {
     MonitorLockerEx ml(&_lock, Mutex::_no_safepoint_check_flag);
@@ -211,7 +211,7 @@
                                            CLDClosure* clds,
                                            CodeBlobClosure* blobs) {
 
-  process_java_roots(oops, clds, clds, NULL, blobs, NULL, 0);
+  process_java_roots(oops, clds, clds, ClassUnloading ? NULL : clds, blobs, NULL, 0);
   process_vm_roots(oops, NULL, NULL, 0);
 
   _process_strong_tasks->all_tasks_completed(n_workers());
@@ -238,7 +238,7 @@
                                          CodeBlobClosure* strong_code,
                                          G1GCPhaseTimes* phase_times,
                                          uint worker_i) {
-  assert(thread_stack_clds == NULL || weak_clds == NULL, "There is overlap between those, only one may be set");
+  assert(thread_stack_clds == NULL || weak_clds == NULL || !ClassUnloading, "There is overlap between those, only one may be set");
   // Iterating over the CLDG and the Threads are done early to allow us to
   // first process the strong CLDs and nmethods and then, after a barrier,
   // let the thread process the weak CLDs and nmethods.
--- old/src/share/vm/gc/g1/heapRegion.inline.hpp	2015-06-06 02:21:45.000000000 +0200
+++ new/src/share/vm/gc/g1/heapRegion.inline.hpp	2015-06-06 02:21:45.000000000 +0200
@@ -95,7 +95,7 @@
 inline bool
 HeapRegion::block_is_obj(const HeapWord* p) const {
   G1CollectedHeap* g1h = G1CollectedHeap::heap();
-  if (ClassUnloadingWithConcurrentMark) {
+  if (ClassUnloading && ClassUnloadingWithConcurrentMark) {
     return !g1h->is_obj_dead(oop(p), this);
   }
   return p < top();
@@ -111,7 +111,7 @@
     return oop(addr)->size();
   }
 
-  assert(ClassUnloadingWithConcurrentMark,
+  assert(ClassUnloading && ClassUnloadingWithConcurrentMark,
       err_msg("All blocks should be objects if G1 Class Unloading isn't used. "
               "HR: ["PTR_FORMAT", "PTR_FORMAT", "PTR_FORMAT") "
               "addr: " PTR_FORMAT,