Object model specs refactoring (#367)

* Many funcitons take Metadata args as references
* Use specific types for ObjectModel. Remove vm_metadata_used() from
Space.
* add comments for side metadata offsets to objectmodel

Co-authored-by: Javad Amiri <javad.amiri@anu.edu.au>

src/plan/barriers.rs

@@ -53,7 +53,7 @@ impl<E: ProcessEdgesWork> ObjectRememberingBarrier<E> {
     #[inline(always)]
     fn enqueue_node<VM: VMBinding>(&mut self, obj: ObjectReference) {
         if compare_exchange_metadata::<VM>(
-            self.meta,
+            &self.meta,
             obj,
             0b1,
             0b0,

src/plan/gencopy/gc_work.rs

@@ -58,7 +58,7 @@ impl<VM: VMBinding> CopyContext for GenCopyCopyContext<VM> {
         object_forwarding::clear_forwarding_bits::<VM>(obj);
         if !super::NO_SLOW && super::ACTIVE_BARRIER == BarrierSelector::ObjectBarrier {
             store_metadata::<VM>(
-                VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC,
+                &VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC,
                 obj,
                 0b1,
                 None,

src/plan/gencopy/global.rs

@@ -200,7 +200,7 @@ impl<VM: VMBinding> GenCopy<VM> {
     ) -> Self {
         let mut heap = HeapMeta::new(HEAP_START, HEAP_END);
         let gencopy_specs = if super::ACTIVE_BARRIER == BarrierSelector::ObjectBarrier {
-            metadata::extract_side_metadata(&[VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC])
+            metadata::extract_side_metadata(&[*VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC])
         } else {
             vec![]
         };

src/plan/gencopy/mutator.rs

@@ -59,7 +59,7 @@ pub fn create_gencopy_mutator<VM: VMBinding>(
         allocators: Allocators::<VM>::new(mutator_tls, &*mmtk.plan, &config.space_mapping),
         barrier: box ObjectRememberingBarrier::<GenCopyNurseryProcessEdges<VM>>::new(
             mmtk,
-            VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC,
+            *VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC,
         ),
         mutator_tls,
         config,

src/policy/copyspace.rs

@@ -77,8 +77,8 @@ impl<VM: VMBinding> CopySpace<VM> {
         heap: &mut HeapMeta,
     ) -> Self {
         let local_specs = extract_side_metadata(&[
-            VM::VMObjectModel::LOCAL_FORWARDING_BITS_SPEC,
-            VM::VMObjectModel::LOCAL_FORWARDING_POINTER_SPEC,
+            *VM::VMObjectModel::LOCAL_FORWARDING_BITS_SPEC,
+            *VM::VMObjectModel::LOCAL_FORWARDING_POINTER_SPEC,
         ]);
         let common = CommonSpace::new(
             SpaceOptions {

src/policy/immortalspace.rs

@@ -46,14 +46,14 @@ impl<VM: VMBinding> SFT for ImmortalSpace<VM> {
     }
     fn initialize_object_metadata(&self, object: ObjectReference, _alloc: bool) {
         let old_value = load_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+            &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
             object,
             None,
             Some(Ordering::SeqCst),
         );
         let new_value = (old_value & GC_MARK_BIT_MASK) | self.mark_state;
         store_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+            &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
             object,
             new_value,
             None,
@@ -106,7 +106,7 @@ impl<VM: VMBinding> ImmortalSpace<VM> {
                 side_metadata_specs: SideMetadataContext {
                     global: global_side_metadata_specs,
                     local: metadata::extract_side_metadata(&[
-                        VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+                        *VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
                     ]),
                 },
             },
@@ -133,7 +133,7 @@ impl<VM: VMBinding> ImmortalSpace<VM> {
     fn test_and_mark(object: ObjectReference, value: usize) -> bool {
         loop {
             let old_value = load_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+                &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
                 object,
                 None,
                 Some(Ordering::SeqCst),
@@ -143,7 +143,7 @@ impl<VM: VMBinding> ImmortalSpace<VM> {
             }
 
             if compare_exchange_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+                &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
                 object,
                 old_value,
                 old_value ^ GC_MARK_BIT_MASK,

src/policy/largeobjectspace.rs

@@ -52,7 +52,7 @@ impl<VM: VMBinding> SFT for LargeObjectSpace<VM> {
     }
     fn initialize_object_metadata(&self, object: ObjectReference, alloc: bool) {
         let old_value = load_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+            &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
             object,
             None,
             Some(Ordering::SeqCst),
@@ -62,7 +62,7 @@ impl<VM: VMBinding> SFT for LargeObjectSpace<VM> {
             new_value |= NURSERY_BIT;
         }
         store_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+            &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
             object,
             new_value,
             None,
@@ -118,7 +118,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
                 side_metadata_specs: SideMetadataContext {
                     global: global_side_metadata_specs,
                     local: metadata::extract_side_metadata(&[
-                        VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+                        *VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
                     ]),
                 },
             },
@@ -208,7 +208,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
                 MARK_BIT
             };
             let old_value = load_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+                &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
                 object,
                 None,
                 Some(Ordering::SeqCst),
@@ -218,7 +218,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
                 return false;
             }
             if compare_exchange_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+                &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
                 object,
                 old_value,
                 old_value & !LOS_BIT_MASK | value,
@@ -234,7 +234,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
 
     fn test_mark_bit(&self, object: ObjectReference, value: usize) -> bool {
         load_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+            &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
             object,
             None,
             Some(Ordering::SeqCst),
@@ -245,7 +245,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
     /// Check if a given object is in nursery
     fn is_in_nursery(&self, object: ObjectReference) -> bool {
         load_metadata::<VM>(
-            VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+            &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
             object,
             None,
             Some(Ordering::Relaxed),
@@ -257,14 +257,14 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
     fn clear_nursery(&self, object: ObjectReference) {
         loop {
             let old_val = load_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+                &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
                 object,
                 None,
                 Some(Ordering::Relaxed),
             );
             let new_val = old_val & !NURSERY_BIT;
             if compare_exchange_metadata::<VM>(
-                VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
+                &VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC,
                 object,
                 old_val,
                 new_val,

src/policy/mallocspace/global.rs

@@ -149,7 +149,7 @@ impl<VM: VMBinding> MallocSpace<VM> {
                 global: global_side_metadata_specs,
                 local: metadata::extract_side_metadata(&[
                     MetadataSpec::OnSide(ALLOC_SIDE_METADATA_SPEC),
-                    VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+                    *VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
                 ]),
             },
             #[cfg(debug_assertions)]

src/policy/mallocspace/metadata.rs

@@ -73,12 +73,12 @@ pub fn is_alloced(object: ObjectReference) -> bool {
 }
 
 pub fn is_alloced_object(address: Address) -> bool {
-    side_metadata::load_atomic(ALLOC_SIDE_METADATA_SPEC, address, Ordering::SeqCst) == 1
+    side_metadata::load_atomic(&ALLOC_SIDE_METADATA_SPEC, address, Ordering::SeqCst) == 1
 }
 
 pub fn is_marked<VM: VMBinding>(object: ObjectReference) -> bool {
     load_metadata::<VM>(
-        VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+        &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
         object,
         None,
         Some(Ordering::SeqCst),
@@ -87,7 +87,7 @@ pub fn is_marked<VM: VMBinding>(object: ObjectReference) -> bool {
 
 pub fn set_alloc_bit(object: ObjectReference) {
     side_metadata::store_atomic(
-        ALLOC_SIDE_METADATA_SPEC,
+        &ALLOC_SIDE_METADATA_SPEC,
         object.to_address(),
         1,
         Ordering::SeqCst,
@@ -96,7 +96,7 @@ pub fn set_alloc_bit(object: ObjectReference) {
 
 pub fn set_mark_bit<VM: VMBinding>(object: ObjectReference) {
     store_metadata::<VM>(
-        VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+        &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
         object,
         1,
         None,
@@ -106,7 +106,7 @@ pub fn set_mark_bit<VM: VMBinding>(object: ObjectReference) {
 
 pub fn unset_alloc_bit(object: ObjectReference) {
     side_metadata::store_atomic(
-        ALLOC_SIDE_METADATA_SPEC,
+        &ALLOC_SIDE_METADATA_SPEC,
         object.to_address(),
         0,
         Ordering::SeqCst,
@@ -115,7 +115,7 @@ pub fn unset_alloc_bit(object: ObjectReference) {
 
 pub fn unset_mark_bit<VM: VMBinding>(object: ObjectReference) {
     store_metadata::<VM>(
-        VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
+        &VM::VMObjectModel::LOCAL_MARK_BIT_SPEC,
         object,
         0,
         None,

src/scheduler/gc_work.rs

@@ -497,7 +497,7 @@ impl<E: ProcessEdgesWork> GCWork<E::VM> for ProcessModBuf<E> {
         if !self.modbuf.is_empty() {
             for obj in &self.modbuf {
                 compare_exchange_metadata::<E::VM>(
-                    self.meta,
+                    &self.meta,
                     *obj,
                     0b0,
                     0b1,

src/util/metadata/global.rs

@@ -1,10 +1,9 @@
 use crate::util::metadata::side_metadata;
-use crate::vm::ObjectModel;
-use atomic::Ordering;
-
 use crate::util::metadata::side_metadata::SideMetadataSpec;
 use crate::util::ObjectReference;
+use crate::vm::ObjectModel;
 use crate::vm::VMBinding;
+use atomic::Ordering;
 
 use super::header_metadata::HeaderMetadataSpec;
 
@@ -39,7 +38,7 @@ impl MetadataSpec {
 ///
 #[inline(always)]
 pub fn load_metadata<VM: VMBinding>(
-    metadata_spec: MetadataSpec,
+    metadata_spec: &MetadataSpec,
     object: ObjectReference,
     mask: Option<usize>,
     atomic_ordering: Option<Ordering>,
@@ -70,7 +69,7 @@ pub fn load_metadata<VM: VMBinding>(
 ///
 #[inline(always)]
 pub fn store_metadata<VM: VMBinding>(
-    metadata_spec: MetadataSpec,
+    metadata_spec: &MetadataSpec,
     object: ObjectReference,
     val: usize,
     mask: Option<usize>,
@@ -108,7 +107,7 @@ pub fn store_metadata<VM: VMBinding>(
 ///
 #[inline(always)]
 pub fn compare_exchange_metadata<VM: VMBinding>(
-    metadata_spec: MetadataSpec,
+    metadata_spec: &MetadataSpec,
     object: ObjectReference,
     old_val: usize,
     new_val: usize,
@@ -150,7 +149,7 @@ pub fn compare_exchange_metadata<VM: VMBinding>(
 ///
 #[inline(always)]
 pub fn fetch_add_metadata<VM: VMBinding>(
-    metadata_spec: MetadataSpec,
+    metadata_spec: &MetadataSpec,
     object: ObjectReference,
     val: usize,
     order: Ordering,
@@ -178,7 +177,7 @@ pub fn fetch_add_metadata<VM: VMBinding>(
 ///
 #[inline(always)]
 pub fn fetch_sub_metadata<VM: VMBinding>(
-    metadata_spec: MetadataSpec,
+    metadata_spec: &MetadataSpec,
     object: ObjectReference,
     val: usize,
     order: Ordering,

src/util/metadata/header_metadata.rs

@@ -44,7 +44,7 @@ impl fmt::Debug for HeaderMetadataSpec {
 /// This function provides a default implementation for the `load_metadata` method from the `ObjectModel` trait.
 #[inline(always)]
 pub fn load_metadata(
-    metadata_spec: HeaderMetadataSpec,
+    metadata_spec: &HeaderMetadataSpec,
     object: ObjectReference,
     optional_mask: Option<usize>,
     atomic_ordering: Option<Ordering>,
@@ -151,7 +151,7 @@ pub fn load_metadata(
 /// This function provides a default implementation for the `store_metadata` method from the `ObjectModel` trait.
 #[inline(always)]
 pub fn store_metadata(
-    metadata_spec: HeaderMetadataSpec,
+    metadata_spec: &HeaderMetadataSpec,
     object: ObjectReference,
     val: usize,
     optional_mask: Option<usize>,
@@ -353,7 +353,7 @@ pub fn store_metadata(
 /// This function provides a default implementation for the `compare_exchange_metadata` method from the `ObjectModel` trait.
 #[inline(always)]
 pub fn compare_exchange_metadata(
-    metadata_spec: HeaderMetadataSpec,
+    metadata_spec: &HeaderMetadataSpec,
     object: ObjectReference,
     old_metadata: usize,
     new_metadata: usize,
@@ -510,7 +510,7 @@ pub fn compare_exchange_metadata(
 /// This function provides a default implementation for the `fetch_add_metadata` method from the `ObjectModel` trait.
 #[inline(always)]
 pub fn fetch_add_metadata(
-    metadata_spec: HeaderMetadataSpec,
+    metadata_spec: &HeaderMetadataSpec,
     object: ObjectReference,
     val: usize,
     order: Ordering,
@@ -602,7 +602,7 @@ pub fn fetch_add_metadata(
 /// This function provides a default implementation for the `fetch_sub_metadata` method from the `ObjectModel` trait.
 #[inline(always)]
 pub fn fetch_sub_metadata(
-    metadata_spec: HeaderMetadataSpec,
+    metadata_spec: &HeaderMetadataSpec,
     object: ObjectReference,
     val: usize,
     order: Ordering,

src/util/metadata/side_metadata/constants.rs

@@ -51,10 +51,36 @@ pub(super) const CHUNK_MASK: usize = (1 << LOG_BYTES_IN_CHUNK) - 1;
 pub(super) const LOCAL_SIDE_METADATA_PER_CHUNK: usize =
     BYTES_IN_CHUNK >> LOG_LOCAL_SIDE_METADATA_WORST_CASE_RATIO;
 
+// The constants _VM_BASE_ADDRESS depends on the side metadata we use inside mmtk-core.
+// If we add any new side metadata internal to mmtk-core, we need to update this accordingly.
+
+// TODO: We should think if it is possible to update this when we create a new side metadata spec.
+// One issue is that these need to be constants. Possibly we need to use macros or custom build scripts.
+
+// --------------------------------------------------
+//
+// Global Metadata
+//
+// MMTk reserved Global side metadata offsets:
+// [currently empty]
+//
+// --------------------------------------------------
+
 /// The base address for the global side metadata space available to VM bindings, to be used for the per-object metadata.
 /// VM bindings must use this to avoid overlap with core internal global side metadata.
 pub const GLOBAL_SIDE_METADATA_VM_BASE_ADDRESS: Address = GLOBAL_SIDE_METADATA_BASE_ADDRESS;
 
+// --------------------------------------------------
+// PolicySpecific Metadata
+//
+// MMTk reserved PolicySpecific side metadata offsets:
+//
+//  1 - MarkSweep Alloc bit:
+//      - Offset `0x0` on 32-bits
+//      - Offset `LOCAL_SIDE_METADATA_BASE_ADDRESS` on 64-bits
+//
+// --------------------------------------------------
+
 /// The base address for the local side metadata space available to VM bindings, to be used for the per-object metadata.
 /// VM bindings must use this to avoid overlap with core internal local side metadata.
 #[cfg(target_pointer_width = "64")]