Trigger Immix defrag if space utilization is low

src/policy/immix/defrag.rs

@@ -73,13 +73,15 @@ impl Defrag {
         exhausted_reusable_space: bool,
         full_heap_system_gc: bool,
         stress_defrag: bool,
+        immix_util: Option<f64>,
     ) {
         let in_defrag = defrag_enabled
             && (emergency_collection
                 || (collection_attempts > 1)
                 || !exhausted_reusable_space
                 || stress_defrag
-                || (collect_whole_heap && user_triggered && full_heap_system_gc));
+                || (collect_whole_heap && user_triggered && full_heap_system_gc))
+                || (immix_util.is_some() && immix_util.unwrap() < 0.2);
         info!("Defrag: {}", in_defrag);
         probe!(mmtk, immix_defrag, in_defrag);
         self.in_defrag_collection

src/policy/immix/immixspace.rs

@@ -415,6 +415,16 @@ impl<VM: VMBinding> ImmixSpace<VM> {
             self.reusable_blocks.len() == 0,
             full_heap_system_gc,
             *self.common.options.immix_always_defrag,
+            if *self.common.options.count_live_bytes_in_gc {
+                let stats = self.common.global_state.live_bytes_in_last_gc.borrow();
+                if let Some(immix_stats) = stats.get(&self.name()) {
+                    Some(immix_stats.live_bytes as f64 / immix_stats.used_bytes as f64)
+                } else {
+                    None
+                }
+            } else {
+                None
+            }
         );
         self.defrag.in_defrag()
     }