cppgc: Be more conservative in Seeper::FinishIfOutOfWork

Finalizing sweeping can be beneficial to truly end a GC cylce. We
should only finalize in `FinishIfOutOfWork()` though if that would not
introduce any jank. Limit the amount of executing finalizers in that
scenario.

Bug: v8:13294
Change-Id: I0237f6b6017d444c457923d83e85147c58586445
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3902222
Commit-Queue: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Anton Bikineev <bikineev@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83279}

src/heap/cppgc/stats-collector.h

@@ -52,6 +52,7 @@ namespace internal {
   V(MarkVisitCrossThreadPersistents)        \
   V(MarkVisitStack)                         \
   V(MarkVisitRememberedSets)                \
+  V(SweepFinishIfOutOfWork)                 \
   V(SweepInvokePreFinalizers)               \
   V(SweepIdleStep)                          \
   V(SweepInTask)                            \

src/heap/cppgc/sweeper.cc

@@ -400,7 +400,7 @@ class SweepFinalizer final {
   bool FinalizeSpaceWithDeadline(SpaceState* space_state,
                                  double deadline_in_seconds) {
     DCHECK(platform_);
-    static constexpr size_t kDeadlineCheckInterval = 8;
+    static constexpr size_t kDeadlineCheckInterval = 4;
     size_t page_count = 1;
 
     while (auto page_state = space_state->swept_unfinalized_pages.Pop()) {
@@ -543,7 +543,7 @@ class MutatorThreadSweeper final : private HeapVisitor<MutatorThreadSweeper> {
 
  private:
   bool SweepSpaceWithDeadline(SpaceState* state, double deadline_in_seconds) {
-    static constexpr size_t kDeadlineCheckInterval = 8;
+    static constexpr size_t kDeadlineCheckInterval = 4;
     size_t page_count = 1;
     while (auto page = state->unswept_pages.Pop()) {
       Traverse(**page);
@@ -884,6 +884,8 @@ class Sweeper::SweeperImpl final {
     if (is_in_progress_ && !is_sweeping_on_mutator_thread_ &&
         concurrent_sweeper_handle_ && concurrent_sweeper_handle_->IsValid() &&
         !concurrent_sweeper_handle_->IsActive()) {
+      StatsCollector::EnabledScope stats_scope(
+          stats_collector_, StatsCollector::kSweepFinishIfOutOfWork);
       // At this point we know that the concurrent sweeping task has run
       // out-of-work: all pages are swept. The main thread still needs to finish
       // sweeping though.
@@ -891,7 +893,19 @@ class Sweeper::SweeperImpl final {
                          [](const SpaceState& state) {
                            return state.unswept_pages.IsEmpty();
                          }));
-      FinishIfRunning();
+
+      // There may be unfinalized pages left. Since it's hard to estimate
+      // the actual amount of sweeping necessary, we sweep with a small
+      // deadline to see if sweeping can be fully finished.
+      MutatorThreadSweeper sweeper(heap_.heap(), &space_states_, platform_,
+                                   config_.free_memory_handling);
+      const double deadline =
+          platform_->MonotonicallyIncreasingTime() +
+          v8::base::TimeDelta::FromMilliseconds(2).InSecondsF();
+      if (sweeper.SweepWithDeadline(deadline)) {
+        FinalizeSweep();
+        NotifyDone();
+      }
     }
   }