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Remove redundant clear_nursery() #799

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merged 3 commits into from
May 2, 2023
Merged

Remove redundant clear_nursery() #799

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d14bcf2
remove redundant code & add comment
tianleq May 2, 2023
2e15bd6
Remove unused clear_nursery
qinsoon May 2, 2023
464076d
Add comments for test_and_mark
qinsoon May 2, 2023
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34 changes: 7 additions & 27 deletions src/policy/largeobjectspace.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -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
Expand Down Expand Up @@ -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 {
Expand All @@ -262,6 +266,7 @@ 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,
Expand Down Expand Up @@ -297,31 +302,6 @@ 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 {
Expand Down