From d14bcf20b79850ac12138c5b258c6f530c02edcc Mon Sep 17 00:00:00 2001
From: Tianle Qiu <tianle.qiu@anu.edu.au>
Date: Tue, 2 May 2023 16:14:16 +1000
Subject: [PATCH 1/3] remove redundant code & add comment

---
 src/policy/largeobjectspace.rs | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/src/policy/largeobjectspace.rs b/src/policy/largeobjectspace.rs
index ea4ea66b1d..a6c01d9919 100644
--- a/src/policy/largeobjectspace.rs
+++ b/src/policy/largeobjectspace.rs
@@ -202,11 +202,11 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
             if nursery_object { "is" } else { "is not" }
         );
         if !self.in_nursery_gc || nursery_object {
-            // Note that test_and_mark() has side effects
+            // Note that test_and_mark() has side effects of
+            // clearing nursery bit/moving objects out of logical nursery
             if self.test_and_mark(object, self.mark_state) {
                 trace!("LOS object {} is being marked now", object);
                 self.treadmill.copy(object, nursery_object);
-                self.clear_nursery(object);
                 // We just moved the object out of the logical nursery, mark it as unlogged.
                 if nursery_object && self.common.needs_log_bit {
                     VM::VMObjectModel::GLOBAL_LOG_BIT_SPEC
@@ -262,6 +262,7 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
             if mark_bit == value {
                 return false;
             }
+            // using LOS_BIT_MASK have side effects of clearing nursery bit
             if VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC
                 .compare_exchange_metadata::<VM, u8>(
                     object,

From 2e15bd66c3640aa3a21dfd14b35f1b5c4c5b5b45 Mon Sep 17 00:00:00 2001
From: Yi Lin <qinsoon@gmail.com>
Date: Tue, 2 May 2023 06:43:47 +0000
Subject: [PATCH 2/3] Remove unused clear_nursery

---
 src/policy/largeobjectspace.rs | 25 -------------------------
 1 file changed, 25 deletions(-)

diff --git a/src/policy/largeobjectspace.rs b/src/policy/largeobjectspace.rs
index a6c01d9919..00afef6e21 100644
--- a/src/policy/largeobjectspace.rs
+++ b/src/policy/largeobjectspace.rs
@@ -298,31 +298,6 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
         ) & NURSERY_BIT
             == NURSERY_BIT
     }
-
-    /// Move a given object out of nursery
-    fn clear_nursery(&self, object: ObjectReference) {
-        loop {
-            let old_val = VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC.load_atomic::<VM, u8>(
-                object,
-                None,
-                Ordering::Relaxed,
-            );
-            let new_val = old_val & !NURSERY_BIT;
-            if VM::VMObjectModel::LOCAL_LOS_MARK_NURSERY_SPEC
-                .compare_exchange_metadata::<VM, u8>(
-                    object,
-                    old_val,
-                    new_val,
-                    None,
-                    Ordering::SeqCst,
-                    Ordering::SeqCst,
-                )
-                .is_ok()
-            {
-                break;
-            }
-        }
-    }
 }
 
 fn get_super_page(cell: Address) -> Address {

From 464076daa3606a573e7be4a847490fc1e0ce8b11 Mon Sep 17 00:00:00 2001
From: Yi Lin <qinsoon@gmail.com>
Date: Tue, 2 May 2023 20:11:18 +1200
Subject: [PATCH 3/3] Add comments for test_and_mark

---
 src/policy/largeobjectspace.rs | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/src/policy/largeobjectspace.rs b/src/policy/largeobjectspace.rs
index 00afef6e21..745f6b3db3 100644
--- a/src/policy/largeobjectspace.rs
+++ b/src/policy/largeobjectspace.rs
@@ -246,6 +246,10 @@ impl<VM: VMBinding> LargeObjectSpace<VM> {
         self.acquire(tls, pages)
     }
 
+    /// Test if the object's mark bit is the same as the given value. If it is not the same,
+    /// the method will attemp to mark the object and clear its nursery bit. If the attempt
+    /// succeeds, the method will return true, meaning the object is marked by this invocation.
+    /// Otherwise, it returns false.
     fn test_and_mark(&self, object: ObjectReference, value: u8) -> bool {
         loop {
             let mask = if self.in_nursery_gc {