From 008f2b85ca4b12c4e04e82f380a7ad7486a46efa Mon Sep 17 00:00:00 2001
From: luc-blaeser <luc.blaeser@dfinity.org>
Date: Fri, 27 Jan 2023 11:35:52 +0100
Subject: [PATCH] Optimization

---
 rts/motoko-rts/src/gc/incremental/partitioned_heap.rs  |  4 ++++
 .../src/gc/incremental/phases/evacuation_increment.rs  | 10 +++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/rts/motoko-rts/src/gc/incremental/partitioned_heap.rs b/rts/motoko-rts/src/gc/incremental/partitioned_heap.rs
index 5392e6ca675..c1fdf81e037 100644
--- a/rts/motoko-rts/src/gc/incremental/partitioned_heap.rs
+++ b/rts/motoko-rts/src/gc/incremental/partitioned_heap.rs
@@ -83,6 +83,10 @@ impl Partition {
         self.dynamic_size
     }
 
+    pub fn marked_size(&self) -> usize {
+        self.marked_size
+    }
+
     pub fn free_size(&self) -> usize {
         self.end_address() - self.dynamic_space_end()
     }
diff --git a/rts/motoko-rts/src/gc/incremental/phases/evacuation_increment.rs b/rts/motoko-rts/src/gc/incremental/phases/evacuation_increment.rs
index 9c914ed888a..18c4eb71531 100644
--- a/rts/motoko-rts/src/gc/incremental/phases/evacuation_increment.rs
+++ b/rts/motoko-rts/src/gc/incremental/phases/evacuation_increment.rs
@@ -70,6 +70,9 @@ impl<'a, M: Memory + 'a> EvacuationIncrement<'a, M> {
     pub unsafe fn evacuate_partition(&mut self, partition: &Partition) {
         debug_assert!(!partition.is_free());
         debug_assert!(!partition.has_large_content());
+        if partition.marked_size() == 0 {
+            return;
+        }
         let mut iterator = PartitionIterator::load_from(partition, &self.state, &mut self.time);
         while iterator.current_object().is_some() && !self.time.is_over() {
             let object = iterator.current_object().unwrap();
@@ -92,7 +95,12 @@ impl<'a, M: Memory + 'a> EvacuationIncrement<'a, M> {
         (*original).forward = new_address;
         debug_assert!(!copy.is_forwarded());
         debug_assert!(original.is_forwarded());
-        debug_assert!(copy.is_marked()); // Necessary to ensure field updates in the copy.
+        // The mark bit is necessary to ensure field updates in the copy.
+        debug_assert!(copy.is_marked());
+        // However, updating the marked size statistics of target partition
+        // can be skipped, since that partition will not be considered for
+        // evacuation during the current GC run.
+
         self.time.advance(size.as_usize());
 
         #[cfg(debug_assertions)]