8261501: Shenandoah: reconsider heap statistics memory ordering

Reviewed-by: rkennke

src/hotspot/share/gc/shenandoah/shenandoahHeap.cpp

@@ -620,12 +620,11 @@ void ShenandoahHeap::post_initialize() {
 }
 
 size_t ShenandoahHeap::used() const {
-  return Atomic::load_acquire(&_used);
+  return Atomic::load(&_used);
 }
 
 size_t ShenandoahHeap::committed() const {
-  OrderAccess::acquire();
+  return Atomic::load(&_committed);
-  return _committed;
 }
 
 void ShenandoahHeap::increase_committed(size_t bytes) {
@@ -639,20 +638,20 @@ void ShenandoahHeap::decrease_committed(size_t bytes) {
 }
 
 void ShenandoahHeap::increase_used(size_t bytes) {
-  Atomic::add(&_used, bytes);
+  Atomic::add(&_used, bytes, memory_order_relaxed);
 }
 
 void ShenandoahHeap::set_used(size_t bytes) {
-  Atomic::release_store_fence(&_used, bytes);
+  Atomic::store(&_used, bytes);
 }
 
 void ShenandoahHeap::decrease_used(size_t bytes) {
   assert(used() >= bytes, "never decrease heap size by more than we've left");
-  Atomic::sub(&_used, bytes);
+  Atomic::sub(&_used, bytes, memory_order_relaxed);
 }
 
 void ShenandoahHeap::increase_allocated(size_t bytes) {
-  Atomic::add(&_bytes_allocated_since_gc_start, bytes);
+  Atomic::add(&_bytes_allocated_since_gc_start, bytes, memory_order_relaxed);
 }
 
 void ShenandoahHeap::notify_mutator_alloc_words(size_t words, bool waste) {
@@ -1883,11 +1882,11 @@ address ShenandoahHeap::gc_state_addr() {
 }
 
 size_t ShenandoahHeap::bytes_allocated_since_gc_start() {
-  return Atomic::load_acquire(&_bytes_allocated_since_gc_start);
+  return Atomic::load(&_bytes_allocated_since_gc_start);
 }
 
 void ShenandoahHeap::reset_bytes_allocated_since_gc_start() {
-  Atomic::release_store_fence(&_bytes_allocated_since_gc_start, (size_t)0);
+  Atomic::store(&_bytes_allocated_since_gc_start, (size_t)0);
 }
 
 void ShenandoahHeap::set_degenerated_gc_in_progress(bool in_progress) {