8027675: Full collections with Serial slower in JDK 8 compared to 7u40

Summary: Reduced the number of calls to follow_class_loader and instead marked and pushed the klass holder directly. Also removed unneeded calls to adjust_klass.
Reviewed-by: coleenp, jmasa, mgerdin, tschatzl

src/share/vm/gc_implementation/shared/markSweep.cpp

@@ -66,29 +66,10 @@ void MarkSweep::AdjustKlassClosure::do_klass(Klass* klass) {
   klass->oops_do(&MarkSweep::adjust_pointer_closure);
 }
 
-void MarkSweep::follow_klass(Klass* klass) {
-  ClassLoaderData* cld = klass->class_loader_data();
-  // The actual processing of the klass is done when we
-  // traverse the list of Klasses in the class loader data.
-  MarkSweep::follow_class_loader(cld);
-}
-
-void MarkSweep::adjust_klass(Klass* klass) {
-  ClassLoaderData* cld = klass->class_loader_data();
-  // The actual processing of the klass is done when we
-  // traverse the list of Klasses in the class loader data.
-  MarkSweep::adjust_class_loader(cld);
-}
-
 void MarkSweep::follow_class_loader(ClassLoaderData* cld) {
   cld->oops_do(&MarkSweep::mark_and_push_closure, &MarkSweep::follow_klass_closure, true);
 }
 
-void MarkSweep::adjust_class_loader(ClassLoaderData* cld) {
-  cld->oops_do(&MarkSweep::adjust_pointer_closure, &MarkSweep::adjust_klass_closure, true);
-}
-
-
 void MarkSweep::follow_stack() {
   do {
     while (!_marking_stack.is_empty()) {

src/share/vm/gc_implementation/shared/markSweep.hpp

@@ -172,10 +172,8 @@ class MarkSweep : AllStatic {
   static void follow_stack();   // Empty marking stack.
 
   static void follow_klass(Klass* klass);
-  static void adjust_klass(Klass* klass);
 
   static void follow_class_loader(ClassLoaderData* cld);
-  static void adjust_class_loader(ClassLoaderData* cld);
 
   static void preserve_mark(oop p, markOop mark);
                                 // Save the mark word so it can be restored later

src/share/vm/gc_implementation/shared/markSweep.inline.hpp

@@ -44,6 +44,11 @@ inline void MarkSweep::mark_object(oop obj) {
   }
 }
 
+inline void MarkSweep::follow_klass(Klass* klass) {
+  oop op = klass->klass_holder();
+  MarkSweep::mark_and_push(&op);
+}
+
 template <class T> inline void MarkSweep::follow_root(T* p) {
   assert(!Universe::heap()->is_in_reserved(p),
          "roots shouldn't be things within the heap");

src/share/vm/oops/instanceKlass.cpp

@@ -2157,7 +2157,6 @@ int InstanceKlass::oop_adjust_pointers(oop obj) {
     obj, \
     MarkSweep::adjust_pointer(p), \
     assert_is_in)
-  MarkSweep::adjust_klass(obj->klass());
   return size;
 }
 

src/share/vm/oops/instanceMirrorKlass.cpp

@@ -155,7 +155,13 @@ void InstanceMirrorKlass::oop_follow_contents(oop obj) {
   // Follow the klass field in the mirror.
   Klass* klass = java_lang_Class::as_Klass(obj);
   if (klass != NULL) {
-    MarkSweep::follow_klass(klass);
+    // For anonymous classes we need to handle the class loader data,
+    // otherwise it won't be claimed and can be unloaded.
+    if (klass->oop_is_instance() && InstanceKlass::cast(klass)->is_anonymous()) {
+      MarkSweep::follow_class_loader(klass->class_loader_data());
+    } else {
+      MarkSweep::follow_klass(klass);
+    }
   } else {
     // If klass is NULL then this a mirror for a primitive type.
     // We don't have to follow them, since they are handled as strong
@@ -196,17 +202,6 @@ int InstanceMirrorKlass::oop_adjust_pointers(oop obj) {
   int size = oop_size(obj);
   InstanceKlass::oop_adjust_pointers(obj);
 
-  // Follow the klass field in the mirror.
-  Klass* klass = java_lang_Class::as_Klass(obj);
-  if (klass != NULL) {
-    MarkSweep::adjust_klass(klass);
-  } else {
-    // If klass is NULL then this a mirror for a primitive type.
-    // We don't have to follow them, since they are handled as strong
-    // roots in Universe::oops_do.
-    assert(java_lang_Class::is_primitive(obj), "Sanity check");
-  }
-
   InstanceMirrorKlass_OOP_ITERATE(                                                    \
     start_of_static_fields(obj), java_lang_Class::static_oop_field_count(obj),        \
     MarkSweep::adjust_pointer(p),                                                     \

src/share/vm/oops/objArrayKlass.cpp

@@ -569,7 +569,6 @@ int ObjArrayKlass::oop_adjust_pointers(oop obj) {
   // Get size before changing pointers.
   // Don't call size() or oop_size() since that is a virtual call.
   int size = a->object_size();
-  MarkSweep::adjust_klass(a->klass());
   ObjArrayKlass_OOP_ITERATE(a, p, MarkSweep::adjust_pointer(p))
   return size;
 }