heap: Add flag for disabling reclamation of unmodified wrappers

Bug: chromium:1107901
Change-Id: Ieacea3dd60e80143a0cbeebf4ab5f91d3888e1a0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2310351
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Auto-Submit: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68974}

src/flags/flag-definitions.h

@@ -1070,6 +1070,9 @@ DEFINE_INT(stress_scavenge, 0,
            "percent of the new space capacity")
 DEFINE_IMPLICATION(fuzzer_gc_analysis, stress_marking)
 DEFINE_IMPLICATION(fuzzer_gc_analysis, stress_scavenge)
+DEFINE_BOOL(
+    reclaim_unmodified_wrappers, true,
+    "reclaim otherwise unreachable unmodified wrapper objects when possible")
 
 // These flags will be removed after experiments. Do not rely on them.
 DEFINE_BOOL(gc_experiment_background_schedule, false,

src/handles/global-handles.cc

@@ -1221,6 +1221,8 @@ void GlobalHandles::IterateWeakRootsIdentifyFinalizers(
 
 void GlobalHandles::IdentifyWeakUnmodifiedObjects(
     WeakSlotCallback is_unmodified) {
+  if (!FLAG_reclaim_unmodified_wrappers) return;
+
   LocalEmbedderHeapTracer* const tracer =
       isolate()->heap()->local_embedder_heap_tracer();
   for (TracedNode* node : traced_young_nodes_) {
@@ -1254,7 +1256,7 @@ void GlobalHandles::IterateYoungStrongAndDependentRoots(RootVisitor* v) {
   }
 }
 
-void GlobalHandles::MarkYoungWeakUnmodifiedObjectsPending(
+void GlobalHandles::MarkYoungWeakDeadObjectsPending(
     WeakSlotCallbackWithHeap is_dead) {
   for (Node* node : young_nodes_) {
     DCHECK(node->is_in_young_list());
@@ -1266,8 +1268,7 @@ void GlobalHandles::MarkYoungWeakUnmodifiedObjectsPending(
   }
 }
 
-void GlobalHandles::IterateYoungWeakUnmodifiedRootsForFinalizers(
-    RootVisitor* v) {
+void GlobalHandles::IterateYoungWeakDeadObjectsForFinalizers(RootVisitor* v) {
   for (Node* node : young_nodes_) {
     DCHECK(node->is_in_young_list());
     if (node->IsWeakRetainer() && (node->state() == Node::PENDING)) {
@@ -1280,7 +1281,7 @@ void GlobalHandles::IterateYoungWeakUnmodifiedRootsForFinalizers(
   }
 }
 
-void GlobalHandles::IterateYoungWeakUnmodifiedRootsForPhantomHandles(
+void GlobalHandles::IterateYoungWeakObjectsForPhantomHandles(
     RootVisitor* v, WeakSlotCallbackWithHeap should_reset_handle) {
   for (Node* node : young_nodes_) {
     DCHECK(node->is_in_young_list());
@@ -1305,6 +1306,8 @@ void GlobalHandles::IterateYoungWeakUnmodifiedRootsForPhantomHandles(
     }
   }
 
+  if (!FLAG_reclaim_unmodified_wrappers) return;
+
   LocalEmbedderHeapTracer* const tracer =
       isolate()->heap()->local_embedder_heap_tracer();
   for (TracedNode* node : traced_young_nodes_) {

src/handles/global-handles.h

@@ -162,12 +162,12 @@ class V8_EXPORT_PRIVATE GlobalHandles final {
   void IterateYoungStrongAndDependentRoots(RootVisitor* v);
 
   // Marks weak unmodified handles satisfying |is_dead| as pending.
-  void MarkYoungWeakUnmodifiedObjectsPending(WeakSlotCallbackWithHeap is_dead);
+  void MarkYoungWeakDeadObjectsPending(WeakSlotCallbackWithHeap is_dead);
 
   // Iterates over weak independent or unmodified handles.
   // See the note above.
-  void IterateYoungWeakUnmodifiedRootsForFinalizers(RootVisitor* v);
-  void IterateYoungWeakUnmodifiedRootsForPhantomHandles(
+  void IterateYoungWeakDeadObjectsForFinalizers(RootVisitor* v);
+  void IterateYoungWeakObjectsForPhantomHandles(
       RootVisitor* v, WeakSlotCallbackWithHeap should_reset_handle);
 
   // Identify unmodified objects that are in weak state and marks them

src/heap/mark-compact.cc

@@ -5018,14 +5018,12 @@ void MinorMarkCompactCollector::MarkLiveObjects() {
 
   {
     TRACE_GC(heap()->tracer(), GCTracer::Scope::MINOR_MC_MARK_GLOBAL_HANDLES);
-    isolate()->global_handles()->MarkYoungWeakUnmodifiedObjectsPending(
+    isolate()->global_handles()->MarkYoungWeakDeadObjectsPending(
         &IsUnmarkedObjectForYoungGeneration);
-    isolate()->global_handles()->IterateYoungWeakUnmodifiedRootsForFinalizers(
+    isolate()->global_handles()->IterateYoungWeakDeadObjectsForFinalizers(
         &root_visitor);
-    isolate()
-        ->global_handles()
-        ->IterateYoungWeakUnmodifiedRootsForPhantomHandles(
-            &root_visitor, &IsUnmarkedObjectForYoungGeneration);
+    isolate()->global_handles()->IterateYoungWeakObjectsForPhantomHandles(
+        &root_visitor, &IsUnmarkedObjectForYoungGeneration);
     DrainMarkingWorklist();
   }
 

src/heap/scavenger.cc

@@ -340,17 +340,16 @@ void ScavengerCollector::CollectGarbage() {
       // Scavenge weak global handles.
       TRACE_GC(heap_->tracer(),
                GCTracer::Scope::SCAVENGER_SCAVENGE_WEAK_GLOBAL_HANDLES_PROCESS);
-      isolate_->global_handles()->MarkYoungWeakUnmodifiedObjectsPending(
+      isolate_->global_handles()->MarkYoungWeakDeadObjectsPending(
           &IsUnscavengedHeapObjectSlot);
-      isolate_->global_handles()->IterateYoungWeakUnmodifiedRootsForFinalizers(
+      isolate_->global_handles()->IterateYoungWeakDeadObjectsForFinalizers(
           &root_scavenge_visitor);
       scavengers[kMainThreadId]->Process();
 
       DCHECK(copied_list.IsEmpty());
       DCHECK(promotion_list.IsEmpty());
-      isolate_->global_handles()
-          ->IterateYoungWeakUnmodifiedRootsForPhantomHandles(
-              &root_scavenge_visitor, &IsUnscavengedHeapObjectSlot);
+      isolate_->global_handles()->IterateYoungWeakObjectsForPhantomHandles(
+          &root_scavenge_visitor, &IsUnscavengedHeapObjectSlot);
     }
 
     {