cppgc: Collect heap statistics

HeapBase::CollectStatistics returns a HeapStatistics struct that can be
used by blink to populate a memory dump.

Bug: chromium:1056170
Change-Id: Ic147a02ba6b4aa77bf92cfca067da70b7e1af55b
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2689181
Commit-Queue: Omer Katz <omerkatz@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#72660}

BUILD.gn

@@ -4666,6 +4666,7 @@ v8_source_set("cppgc_base") {
     "include/cppgc/garbage-collected.h",
     "include/cppgc/heap-consistency.h",
     "include/cppgc/heap-state.h",
+    "include/cppgc/heap-statistics.h",
     "include/cppgc/heap.h",
     "include/cppgc/internal/api-constants.h",
     "include/cppgc/internal/atomic-entry-flag.h",
@@ -4719,6 +4720,8 @@ v8_source_set("cppgc_base") {
     "src/heap/cppgc/heap-space.cc",
     "src/heap/cppgc/heap-space.h",
     "src/heap/cppgc/heap-state.cc",
+    "src/heap/cppgc/heap-statistics-collector.cc",
+    "src/heap/cppgc/heap-statistics-collector.h",
     "src/heap/cppgc/heap-visitor.h",
     "src/heap/cppgc/heap.cc",
     "src/heap/cppgc/heap.h",

include/DEPS

@@ -4,6 +4,7 @@ include_rules = [
   "+cppgc/common.h",
   # Used by v8-cppgc.h to bridge to cppgc.
   "+cppgc/custom-space.h",
+  "+cppgc/heap-statistics.h",
   "+cppgc/internal/process-heap.h",
   "+cppgc/internal/write-barrier.h",
   "+cppgc/visitor.h",

include/cppgc/heap-statistics.h

@@ -0,0 +1,110 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef INCLUDE_CPPGC_HEAP_STATISTICS_H_
+#define INCLUDE_CPPGC_HEAP_STATISTICS_H_
+
+#include <memory>
+#include <string>
+#include <vector>
+
+namespace cppgc {
+
+/**
+ * `HeapStatistics` contains memory consumption and utilization statistics for a
+ * cppgc heap.
+ */
+struct HeapStatistics final {
+  /**
+   * Specifies the detail level of the heap statistics. Brief statistics contain
+   * only the top-level allocated and used memory statistics for the entire
+   * heap. Detailed statistics also contain a break down per space and page, as
+   * well as freelist statistics and object type histograms. Note that used
+   * memory reported by brief statistics and detailed statistics might differ
+   * slightly.
+   */
+  enum DetailLevel : uint8_t {
+    kBrief,
+    kDetailed,
+  };
+
+  /**
+   * Statistics of object types. For each type the statistics record its name,
+   * how many objects of that type were allocated, and the overall size used by
+   * these objects.
+   */
+  struct ObjectStatistics {
+    /** Number of distinct types in the heap. */
+    size_t num_types = 0;
+    /** Name of each type in the heap. */
+    std::vector<std::string> type_name;
+    /** Number of allocated objects per each type. */
+    std::vector<size_t> type_count;
+    /** Overall size of allocated objects per each type. */
+    std::vector<size_t> type_bytes;
+  };
+
+  /**
+   * Page granularity statistics. For each page the statistics record the
+   * allocated memory size and overall used memory size for the page.
+   */
+  struct PageStatistics {
+    /** Overall amount of memory allocated for the page. */
+    size_t allocated_size_bytes = 0;
+    /** Amount of memory actually used on the page. */
+    size_t used_size_bytes = 0;
+  };
+
+  /**
+   * Stastistics of the freelist (used only in non-large object spaces). For
+   * each bucket in the freelist the statistics record the bucket size, the
+   * number of freelist entries in the bucket, and the overall allocated memory
+   * consumed by these freelist entries.
+   */
+  struct FreeListStatistics {
+    /** bucket sizes in the freelist. */
+    std::vector<size_t> bucket_size;
+    /** number of freelist entries per bucket. */
+    std::vector<size_t> free_count;
+    /** memory size concumed by freelist entries per size. */
+    std::vector<size_t> free_size;
+  };
+
+  /**
+   * Space granularity statistics. For each space the statistics record the
+   * space name, the amount of allocated memory and overall used memory for the
+   * space. The statistics also contain statistics for each of the space's
+   * pages, its freelist and the objects allocated on the space.
+   */
+  struct SpaceStatistics {
+    /** The space name */
+    std::string name;
+    /** Overall amount of memory allocated for the space. */
+    size_t allocated_size_bytes = 0;
+    /** Amount of memory actually used on the space. */
+    size_t used_size_bytes = 0;
+    /** Statistics for each of the pages in the space. */
+    std::vector<PageStatistics> page_stats;
+    /** Statistics for the freelist of the space. */
+    FreeListStatistics free_list_stats;
+    /** Statistics for object allocated on the space. Filled only when
+     * NameProvider::HideInternalNames() is false. */
+    ObjectStatistics object_stats;
+  };
+
+  /** Overall amount of memory allocated for the heap. */
+  size_t allocated_size_bytes = 0;
+  /** Amount of memory actually used on the heap. */
+  size_t used_size_bytes = 0;
+  /** Detail level of this HeapStatistics. */
+  DetailLevel detail_level;
+
+  /** Statistics for each of the spaces in the heap. Filled only when
+   * detail_level is kDetailed. */
+  std::vector<SpaceStatistics> space_stats;
+};
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_HEAP_STATISTICS_H_

include/v8-cppgc.h

@@ -10,6 +10,7 @@
 #include <vector>
 
 #include "cppgc/custom-space.h"
+#include "cppgc/heap-statistics.h"
 #include "cppgc/internal/process-heap.h"
 #include "cppgc/internal/write-barrier.h"
 #include "cppgc/visitor.h"
@@ -106,6 +107,15 @@ class V8_EXPORT CppHeap {
    */
   void Terminate();
 
+  /**
+   * \param detail_level specifies whether should return detailed
+   *   statistics or only brief summary statistics.
+   * \returns current CppHeap statistics regarding memory consumption
+   *   and utilization.
+   */
+  cppgc::HeapStatistics CollectStatistics(
+      cppgc::HeapStatistics::DetailLevel detail_level);
+
  private:
   CppHeap() = default;
 

src/heap/cppgc-js/cpp-heap.cc

@@ -58,6 +58,12 @@ cppgc::HeapHandle& CppHeap::GetHeapHandle() {
 
 void CppHeap::Terminate() { internal::CppHeap::From(this)->Terminate(); }
 
+cppgc::HeapStatistics CppHeap::CollectStatistics(
+    cppgc::HeapStatistics::DetailLevel detail_level) {
+  return internal::CppHeap::From(this)->AsBase().CollectStatistics(
+      detail_level);
+}
+
 void JSHeapConsistency::DijkstraMarkingBarrierSlow(
     cppgc::HeapHandle& heap_handle, const TracedReferenceBase& ref) {
   auto& heap_base = cppgc::internal::HeapBase::From(heap_handle);

src/heap/cppgc/free-list.cc

@@ -191,5 +191,26 @@ bool FreeList::IsConsistent(size_t index) const {
           !free_list_tails_[index]->Next());
 }
 
+void FreeList::CollectStatistics(
+    HeapStatistics::FreeListStatistics& free_list_stats) {
+  std::vector<size_t>& bucket_size = free_list_stats.bucket_size;
+  std::vector<size_t>& free_count = free_list_stats.free_count;
+  std::vector<size_t>& free_size = free_list_stats.free_size;
+  DCHECK(bucket_size.empty());
+  DCHECK(free_count.empty());
+  DCHECK(free_size.empty());
+  for (size_t i = 0; i < kPageSizeLog2; ++i) {
+    size_t entry_count = 0;
+    size_t entry_size = 0;
+    for (Entry* entry = free_list_heads_[i]; entry; entry = entry->Next()) {
+      ++entry_count;
+      entry_size += entry->GetSize();
+    }
+    bucket_size.push_back(static_cast<size_t>(1) << i);
+    free_count.push_back(entry_count);
+    free_size.push_back(entry_size);
+  }
+}
+
 }  // namespace internal
 }  // namespace cppgc

src/heap/cppgc/free-list.h

@@ -7,6 +7,7 @@
 
 #include <array>
 
+#include "include/cppgc/heap-statistics.h"
 #include "src/base/macros.h"
 #include "src/heap/cppgc/globals.h"
 #include "src/heap/cppgc/heap-object-header.h"
@@ -45,6 +46,8 @@ class V8_EXPORT_PRIVATE FreeList {
 
   bool Contains(Block) const;
 
+  void CollectStatistics(HeapStatistics::FreeListStatistics&);
+
  private:
   class Entry;
 

src/heap/cppgc/gc-info-table.h

@@ -63,7 +63,8 @@ class V8_EXPORT GCInfoTable final {
     return table_[index];
   }
 
-  GCInfoIndex NumberOfGCInfosForTesting() const { return current_index_; }
+  GCInfoIndex NumberOfGCInfos() const { return current_index_; }
+
   GCInfoIndex LimitForTesting() const { return limit_; }
   GCInfo& TableSlotForTesting(GCInfoIndex index) { return table_[index]; }
 

src/heap/cppgc/heap-base.cc

@@ -10,6 +10,7 @@
 #include "src/heap/cppgc/globals.h"
 #include "src/heap/cppgc/heap-object-header.h"
 #include "src/heap/cppgc/heap-page.h"
+#include "src/heap/cppgc/heap-statistics-collector.h"
 #include "src/heap/cppgc/heap-visitor.h"
 #include "src/heap/cppgc/marker.h"
 #include "src/heap/cppgc/marking-verifier.h"
@@ -133,5 +134,19 @@ void HeapBase::Terminate() {
   disallow_gc_scope_++;
 }
 
+HeapStatistics HeapBase::CollectStatistics(
+    HeapStatistics::DetailLevel detail_level) {
+  if (detail_level == HeapStatistics::DetailLevel::kBrief) {
+    return {stats_collector_->allocated_memory_size(),
+            stats_collector_->allocated_object_size(),
+            HeapStatistics::DetailLevel::kBrief,
+            {}};
+  }
+
+  sweeper_.FinishIfRunning();
+  object_allocator_.ResetLinearAllocationBuffers();
+  return HeapStatisticsCollector().CollectStatistics(this);
+}
+
 }  // namespace internal
 }  // namespace cppgc

src/heap/cppgc/heap-base.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <set>
 
+#include "include/cppgc/heap-statistics.h"
 #include "include/cppgc/heap.h"
 #include "include/cppgc/internal/persistent-node.h"
 #include "include/cppgc/macros.h"
@@ -163,6 +164,8 @@ class V8_EXPORT_PRIVATE HeapBase : public cppgc::HeapHandle {
   void EnableTestingAPIsForTesting() { testing_enabled_ = true; }
   bool TestingEnabled() const { return testing_enabled_; }
 
+  HeapStatistics CollectStatistics(HeapStatistics::DetailLevel);
+
  protected:
   virtual void FinalizeIncrementalGarbageCollectionIfNeeded(
       cppgc::Heap::StackState) = 0;

src/heap/cppgc/heap-page.cc

@@ -179,13 +179,12 @@ LargePage::LargePage(HeapBase* heap, BaseSpace* space, size_t size)
 
 LargePage::~LargePage() = default;
 
-namespace {
-size_t LargePageAllocationSize(size_t payload_size) {
+// static
+size_t LargePage::AllocationSize(size_t payload_size) {
   const size_t page_header_size =
       RoundUp(sizeof(LargePage), kAllocationGranularity);
   return page_header_size + payload_size;
 }
-}  // namespace
 
 // static
 LargePage* LargePage::Create(PageBackend* page_backend, LargePageSpace* space,
@@ -194,14 +193,14 @@ LargePage* LargePage::Create(PageBackend* page_backend, LargePageSpace* space,
   DCHECK_NOT_NULL(space);
   DCHECK_LE(kLargeObjectSizeThreshold, size);
 
-  const size_t allocation_size = LargePageAllocationSize(size);
+  const size_t allocation_size = AllocationSize(size);
 
   auto* heap = space->raw_heap()->heap();
   void* memory = page_backend->AllocateLargePageMemory(allocation_size);
   LargePage* page = new (memory) LargePage(heap, space, size);
   page->SynchronizedStore();
   page->heap()->stats_collector()->NotifyAllocatedMemory(
-      LargePageAllocationSize(page->PayloadSize()));
+      AllocationSize(page->PayloadSize()));
   return page;
 }
 
@@ -215,7 +214,7 @@ void LargePage::Destroy(LargePage* page) {
   page->~LargePage();
   PageBackend* backend = page->heap()->page_backend();
   page->heap()->stats_collector()->NotifyFreedMemory(
-      LargePageAllocationSize(page->PayloadSize()));
+      AllocationSize(page->PayloadSize()));
   backend->FreeLargePageMemory(reinterpret_cast<Address>(page));
 }
 

src/heap/cppgc/heap-page.h

@@ -185,6 +185,8 @@ class V8_EXPORT_PRIVATE NormalPage final : public BasePage {
 
 class V8_EXPORT_PRIVATE LargePage final : public BasePage {
  public:
+  // Returns the allocation size required for a payload of size |size|.
+  static size_t AllocationSize(size_t size);
   // Allocates a new page in the detached state.
   static LargePage* Create(PageBackend*, LargePageSpace*, size_t);
   // Destroys and frees the page. The page must be detached from the

src/heap/cppgc/heap-statistics-collector.cc

@@ -0,0 +1,158 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/heap/cppgc/heap-statistics-collector.h"
+
+#include <string>
+
+#include "include/cppgc/name-provider.h"
+#include "src/heap/cppgc/free-list.h"
+#include "src/heap/cppgc/heap-base.h"
+#include "src/heap/cppgc/heap-object-header.h"
+#include "src/heap/cppgc/raw-heap.h"
+#include "src/heap/cppgc/stats-collector.h"
+
+namespace cppgc {
+namespace internal {
+
+namespace {
+
+std::string GetNormalPageSpaceName(size_t index) {
+  // Check that space is not a large object space.
+  DCHECK_NE(RawHeap::kNumberOfRegularSpaces - 1, index);
+  // Handle regular normal page spaces.
+  if (index < RawHeap::kNumberOfRegularSpaces) {
+    return "NormalPageSpace" + std::to_string(index);
+  }
+  // Space is a custom space.
+  return "CustomSpace" +
+         std::to_string(index - RawHeap::kNumberOfRegularSpaces);
+}
+
+HeapStatistics::SpaceStatistics* InitializeSpace(HeapStatistics* stats,
+                                                 std::string name) {
+  stats->space_stats.emplace_back();
+  HeapStatistics::SpaceStatistics* space_stats = &stats->space_stats.back();
+  space_stats->name = std::move(name);
+
+  if (!NameProvider::HideInternalNames()) {
+    const size_t num_types = GlobalGCInfoTable::Get().NumberOfGCInfos();
+    space_stats->object_stats.num_types = num_types;
+    space_stats->object_stats.type_name.resize(num_types);
+    space_stats->object_stats.type_count.resize(num_types);
+    space_stats->object_stats.type_bytes.resize(num_types);
+  }
+
+  return space_stats;
+}
+
+void FinalizePage(HeapStatistics::SpaceStatistics* space_stats,
+                  HeapStatistics::PageStatistics** page_stats) {
+  if (*page_stats) {
+    DCHECK_NOT_NULL(space_stats);
+    space_stats->allocated_size_bytes += (*page_stats)->allocated_size_bytes;
+    space_stats->used_size_bytes += (*page_stats)->used_size_bytes;
+  }
+  *page_stats = nullptr;
+}
+
+void FinalizeSpace(HeapStatistics* stats,
+                   HeapStatistics::SpaceStatistics** space_stats,
+                   HeapStatistics::PageStatistics** page_stats) {
+  FinalizePage(*space_stats, page_stats);
+  if (*space_stats) {
+    DCHECK_NOT_NULL(stats);
+    stats->allocated_size_bytes += (*space_stats)->allocated_size_bytes;
+    stats->used_size_bytes += (*space_stats)->used_size_bytes;
+  }
+  *space_stats = nullptr;
+}
+
+void RecordObjectType(HeapStatistics::SpaceStatistics* space_stats,
+                      HeapObjectHeader* header, size_t object_size) {
+  if (!NameProvider::HideInternalNames()) {
+    // Detailed names available.
+    GCInfoIndex gc_info_index = header->GetGCInfoIndex();
+    space_stats->object_stats.type_count[gc_info_index]++;
+    space_stats->object_stats.type_bytes[gc_info_index] += object_size;
+    if (space_stats->object_stats.type_name[gc_info_index].empty()) {
+      space_stats->object_stats.type_name[gc_info_index] =
+          header->GetName().value;
+    }
+  }
+}
+
+}  // namespace
+
+HeapStatistics HeapStatisticsCollector::CollectStatistics(HeapBase* heap) {
+  HeapStatistics stats;
+  stats.detail_level = HeapStatistics::DetailLevel::kDetailed;
+  current_stats_ = &stats;
+
+  Traverse(&heap->raw_heap());
+  FinalizeSpace(current_stats_, &current_space_stats_, &current_page_stats_);
+
+  DCHECK_EQ(heap->stats_collector()->allocated_memory_size(),
+            stats.allocated_size_bytes);
+  return stats;
+}
+
+bool HeapStatisticsCollector::VisitNormalPageSpace(NormalPageSpace* space) {
+  DCHECK_EQ(0u, space->linear_allocation_buffer().size());
+
+  FinalizeSpace(current_stats_, &current_space_stats_, &current_page_stats_);
+
+  current_space_stats_ =
+      InitializeSpace(current_stats_, GetNormalPageSpaceName(space->index()));
+
+  space->free_list().CollectStatistics(current_space_stats_->free_list_stats);
+
+  return false;
+}
+
+bool HeapStatisticsCollector::VisitLargePageSpace(LargePageSpace* space) {
+  FinalizeSpace(current_stats_, &current_space_stats_, &current_page_stats_);
+
+  current_space_stats_ = InitializeSpace(current_stats_, "LargePageSpace");
+
+  return false;
+}
+
+bool HeapStatisticsCollector::VisitNormalPage(NormalPage* page) {
+  DCHECK_NOT_NULL(current_space_stats_);
+  FinalizePage(current_space_stats_, &current_page_stats_);
+  current_space_stats_->page_stats.emplace_back(
+      HeapStatistics::PageStatistics{kPageSize, 0});
+  current_page_stats_ = &current_space_stats_->page_stats.back();
+  return false;
+}
+
+bool HeapStatisticsCollector::VisitLargePage(LargePage* page) {
+  DCHECK_NOT_NULL(current_space_stats_);
+  FinalizePage(current_space_stats_, &current_page_stats_);
+  HeapObjectHeader* object_header = page->ObjectHeader();
+  size_t object_size = page->PayloadSize();
+  RecordObjectType(current_space_stats_, object_header, object_size);
+  size_t allocated_size = LargePage::AllocationSize(object_size);
+  current_space_stats_->allocated_size_bytes += allocated_size;
+  current_space_stats_->used_size_bytes += object_size;
+  current_space_stats_->page_stats.emplace_back(
+      HeapStatistics::PageStatistics{allocated_size, object_size});
+
+  return true;
+}
+
+bool HeapStatisticsCollector::VisitHeapObjectHeader(HeapObjectHeader* header) {
+  DCHECK(!header->IsLargeObject());
+  DCHECK_NOT_NULL(current_space_stats_);
+  DCHECK_NOT_NULL(current_page_stats_);
+  if (header->IsFree()) return true;
+  size_t object_size = header->GetSize();
+  RecordObjectType(current_space_stats_, header, object_size);
+  current_page_stats_->used_size_bytes += object_size;
+  return true;
+}
+
+}  // namespace internal
+}  // namespace cppgc

src/heap/cppgc/heap-statistics-collector.h

@@ -0,0 +1,35 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef V8_HEAP_CPPGC_HEAP_STATISTICS_COLLECTOR_H_
+#define V8_HEAP_CPPGC_HEAP_STATISTICS_COLLECTOR_H_
+
+#include "include/cppgc/heap-statistics.h"
+#include "src/heap/cppgc/heap-visitor.h"
+
+namespace cppgc {
+namespace internal {
+
+class HeapStatisticsCollector : private HeapVisitor<HeapStatisticsCollector> {
+  friend class HeapVisitor<HeapStatisticsCollector>;
+
+ public:
+  HeapStatistics CollectStatistics(HeapBase*);
+
+ private:
+  bool VisitNormalPageSpace(NormalPageSpace*);
+  bool VisitLargePageSpace(LargePageSpace*);
+  bool VisitNormalPage(NormalPage*);
+  bool VisitLargePage(LargePage*);
+  bool VisitHeapObjectHeader(HeapObjectHeader*);
+
+  HeapStatistics* current_stats_;
+  HeapStatistics::SpaceStatistics* current_space_stats_ = nullptr;
+  HeapStatistics::PageStatistics* current_page_stats_ = nullptr;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // V8_HEAP_CPPGC_HEAP_STATISTICS_COLLECTOR_H_

src/heap/cppgc/stats-collector.cc

@@ -215,6 +215,10 @@ void StatsCollector::NotifySweepingCompleted() {
   }
 }
 
+size_t StatsCollector::allocated_memory_size() const {
+  return memory_allocated_bytes_;
+}
+
 size_t StatsCollector::allocated_object_size() const {
   // During sweeping we refer to the current Event as that already holds the
   // correct marking information. In all other phases, the previous event holds

src/heap/cppgc/stats-collector.h

@@ -263,6 +263,7 @@ class V8_EXPORT_PRIVATE StatsCollector final {
   // is finished at this point.
   void NotifySweepingCompleted();
 
+  size_t allocated_memory_size() const;
   // Size of live objects in bytes  on the heap. Based on the most recent marked
   // bytes and the bytes allocated since last marking.
   size_t allocated_object_size() const;

test/unittests/BUILD.gn

@@ -100,6 +100,7 @@ v8_source_set("cppgc_unittests_sources") {
     "heap/cppgc/heap-growing-unittest.cc",
     "heap/cppgc/heap-object-header-unittest.cc",
     "heap/cppgc/heap-page-unittest.cc",
+    "heap/cppgc/heap-statistics-collector-unittest.cc",
     "heap/cppgc/heap-unittest.cc",
     "heap/cppgc/incremental-marking-schedule-unittest.cc",
     "heap/cppgc/logging-unittest.cc",

test/unittests/heap/cppgc/gc-info-unittest.cc

@@ -23,7 +23,7 @@ constexpr GCInfo GetEmptyGCInfo() { return {nullptr, nullptr, nullptr, false}; }
 TEST(GCInfoTableTest, InitialEmpty) {
   v8::base::PageAllocator page_allocator;
   GCInfoTable table(&page_allocator);
-  EXPECT_EQ(GCInfoTable::kMinIndex, table.NumberOfGCInfosForTesting());
+  EXPECT_EQ(GCInfoTable::kMinIndex, table.NumberOfGCInfos());
 }
 
 TEST(GCInfoTableTest, ResizeToMaxIndex) {

test/unittests/heap/cppgc/heap-statistics-collector-unittest.cc

@@ -0,0 +1,131 @@
+// Copyright 2021 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "src/heap/cppgc/heap-statistics-collector.h"
+
+#include "include/cppgc/heap-statistics.h"
+#include "src/base/macros.h"
+#include "src/heap/cppgc/globals.h"
+#include "test/unittests/heap/cppgc/tests.h"
+#include "testing/gtest/include/gtest/gtest.h"
+
+namespace cppgc {
+namespace internal {
+
+class HeapStatisticsCollectorTest : public testing::TestWithHeap {};
+
+TEST_F(HeapStatisticsCollectorTest, EmptyHeapBriefStatisitcs) {
+  HeapStatistics brief_stats = Heap::From(GetHeap())->CollectStatistics(
+      HeapStatistics::DetailLevel::kBrief);
+  EXPECT_EQ(HeapStatistics::DetailLevel::kBrief, brief_stats.detail_level);
+  EXPECT_EQ(0u, brief_stats.used_size_bytes);
+  EXPECT_EQ(0u, brief_stats.used_size_bytes);
+  EXPECT_TRUE(brief_stats.space_stats.empty());
+}
+
+TEST_F(HeapStatisticsCollectorTest, EmptyHeapDetailedStatisitcs) {
+  HeapStatistics detailed_stats = Heap::From(GetHeap())->CollectStatistics(
+      HeapStatistics::DetailLevel::kDetailed);
+  EXPECT_EQ(HeapStatistics::DetailLevel::kDetailed,
+            detailed_stats.detail_level);
+  EXPECT_EQ(0u, detailed_stats.used_size_bytes);
+  EXPECT_EQ(0u, detailed_stats.used_size_bytes);
+  EXPECT_EQ(RawHeap::kNumberOfRegularSpaces, detailed_stats.space_stats.size());
+  for (HeapStatistics::SpaceStatistics& space_stats :
+       detailed_stats.space_stats) {
+    EXPECT_EQ(0u, space_stats.used_size_bytes);
+    EXPECT_EQ(0u, space_stats.used_size_bytes);
+    EXPECT_TRUE(space_stats.page_stats.empty());
+    if (space_stats.name == "LargePageSpace") {
+      // Large page space has no free list.
+      EXPECT_TRUE(space_stats.free_list_stats.bucket_size.empty());
+      EXPECT_TRUE(space_stats.free_list_stats.free_count.empty());
+      EXPECT_TRUE(space_stats.free_list_stats.free_size.empty());
+    } else {
+      EXPECT_EQ(kPageSizeLog2, space_stats.free_list_stats.bucket_size.size());
+      EXPECT_EQ(kPageSizeLog2, space_stats.free_list_stats.free_count.size());
+      EXPECT_EQ(kPageSizeLog2, space_stats.free_list_stats.free_size.size());
+    }
+  }
+}
+
+namespace {
+template <size_t Size>
+class GCed : public GarbageCollected<GCed<Size>> {
+ public:
+  void Trace(Visitor*) const {}
+
+ private:
+  char array_[Size];
+};
+}  // namespace
+
+TEST_F(HeapStatisticsCollectorTest, NonEmptyNormalPage) {
+  MakeGarbageCollected<GCed<1>>(GetHeap()->GetAllocationHandle());
+  static constexpr size_t used_size =
+      RoundUp<kAllocationGranularity>(1 + sizeof(HeapObjectHeader));
+  HeapStatistics detailed_stats = Heap::From(GetHeap())->CollectStatistics(
+      HeapStatistics::DetailLevel::kDetailed);
+  EXPECT_EQ(HeapStatistics::DetailLevel::kDetailed,
+            detailed_stats.detail_level);
+  EXPECT_EQ(kPageSize, detailed_stats.allocated_size_bytes);
+  EXPECT_EQ(used_size, detailed_stats.used_size_bytes);
+  EXPECT_EQ(RawHeap::kNumberOfRegularSpaces, detailed_stats.space_stats.size());
+  bool found_non_empty_space = false;
+  for (const HeapStatistics::SpaceStatistics& space_stats :
+       detailed_stats.space_stats) {
+    if (space_stats.page_stats.empty()) {
+      EXPECT_EQ(0u, space_stats.allocated_size_bytes);
+      EXPECT_EQ(0u, space_stats.used_size_bytes);
+      continue;
+    }
+    EXPECT_NE("LargePageSpace", space_stats.name);
+    EXPECT_FALSE(found_non_empty_space);
+    found_non_empty_space = true;
+    EXPECT_EQ(kPageSize, space_stats.allocated_size_bytes);
+    EXPECT_EQ(used_size, space_stats.used_size_bytes);
+    EXPECT_EQ(1u, space_stats.page_stats.size());
+    EXPECT_EQ(kPageSize, space_stats.page_stats.back().allocated_size_bytes);
+    EXPECT_EQ(used_size, space_stats.page_stats.back().used_size_bytes);
+  }
+  EXPECT_TRUE(found_non_empty_space);
+}
+
+TEST_F(HeapStatisticsCollectorTest, NonEmptyLargePage) {
+  MakeGarbageCollected<GCed<kLargeObjectSizeThreshold>>(
+      GetHeap()->GetAllocationHandle());
+  static constexpr size_t used_size = RoundUp<kAllocationGranularity>(
+      kLargeObjectSizeThreshold + sizeof(HeapObjectHeader));
+  static constexpr size_t allocated_size =
+      RoundUp<kAllocationGranularity>(used_size + sizeof(LargePage));
+  HeapStatistics detailed_stats = Heap::From(GetHeap())->CollectStatistics(
+      HeapStatistics::DetailLevel::kDetailed);
+  EXPECT_EQ(HeapStatistics::DetailLevel::kDetailed,
+            detailed_stats.detail_level);
+  EXPECT_EQ(allocated_size, detailed_stats.allocated_size_bytes);
+  EXPECT_EQ(used_size, detailed_stats.used_size_bytes);
+  EXPECT_EQ(RawHeap::kNumberOfRegularSpaces, detailed_stats.space_stats.size());
+  bool found_non_empty_space = false;
+  for (const HeapStatistics::SpaceStatistics& space_stats :
+       detailed_stats.space_stats) {
+    if (space_stats.page_stats.empty()) {
+      EXPECT_EQ(0u, space_stats.allocated_size_bytes);
+      EXPECT_EQ(0u, space_stats.used_size_bytes);
+      continue;
+    }
+    EXPECT_EQ("LargePageSpace", space_stats.name);
+    EXPECT_FALSE(found_non_empty_space);
+    found_non_empty_space = true;
+    EXPECT_EQ(allocated_size, space_stats.allocated_size_bytes);
+    EXPECT_EQ(used_size, space_stats.used_size_bytes);
+    EXPECT_EQ(1u, space_stats.page_stats.size());
+    EXPECT_EQ(allocated_size,
+              space_stats.page_stats.back().allocated_size_bytes);
+    EXPECT_EQ(used_size, space_stats.page_stats.back().used_size_bytes);
+  }
+  EXPECT_TRUE(found_non_empty_space);
+}
+
+}  // namespace internal
+}  // namespace cppgc