cppgc: shared-cage: Remove heap-specific metadata from cage-header

The CL is a prerequisite for the shared cage. Instead of storing
state variables (is_incremental_marking_in_progress,
is_young_generation_enabled) in the cage metadata, the CL moves them to
HeapHandle. The HeapHandle pointer is now retrieved from page-headers.

To make sure that the write-barrier code is better optimized, the
HeapHandle definition is moved to internal/ headers. The part of
BasePage that contains HeapBase (i.e. HeapHandle) pointer is also
extracted and moved to the headers.

Bug: v8:12231
Change-Id: I44bf65d99a621d9548e4250386cf87476ca186ac
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3689730
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Cr-Commit-Position: refs/heads/main@{#81005}

BUILD.bazel

@@ -458,11 +458,14 @@ filegroup(
         "include/cppgc/garbage-collected.h",
         "include/cppgc/heap.h",
         "include/cppgc/heap-consistency.h",
+        "include/cppgc/heap-handle.h",
         "include/cppgc/heap-state.h",
         "include/cppgc/heap-statistics.h",
         "include/cppgc/internal/api-constants.h",
         "include/cppgc/internal/atomic-entry-flag.h",
+        "include/cppgc/internal/base-page-handle.h",
         "include/cppgc/internal/caged-heap-local-data.h",
+        "include/cppgc/internal/caged-heap.h",
         "include/cppgc/internal/compiler-specific.h",
         "include/cppgc/internal/finalizer-trait.h",
         "include/cppgc/internal/gc-info.h",

BUILD.gn

@@ -5667,11 +5667,13 @@ v8_header_set("cppgc_headers") {
     "include/cppgc/explicit-management.h",
     "include/cppgc/garbage-collected.h",
     "include/cppgc/heap-consistency.h",
+    "include/cppgc/heap-handle.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",
+    "include/cppgc/internal/base-page-handle.h",
     "include/cppgc/internal/compiler-specific.h",
     "include/cppgc/internal/finalizer-trait.h",
     "include/cppgc/internal/gc-info.h",
@@ -5701,6 +5703,7 @@ v8_header_set("cppgc_headers") {
 
   if (cppgc_enable_caged_heap) {
     sources += [ "include/cppgc/internal/caged-heap-local-data.h" ]
+    sources += [ "include/cppgc/internal/caged-heap.h" ]
   }
 
   deps = [

include/cppgc/heap-handle.h

@@ -0,0 +1,41 @@
+// Copyright 2022 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_HANDLE_H_
+#define INCLUDE_CPPGC_HEAP_HANDLE_H_
+
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+
+namespace internal {
+class HeapBase;
+class WriteBarrierTypeForCagedHeapPolicy;
+}  // namespace internal
+
+/**
+ * Opaque handle used for additional heap APIs.
+ */
+class HeapHandle {
+ private:
+  HeapHandle() = default;
+
+  V8_INLINE bool is_incremental_marking_in_progress() const {
+    return is_incremental_marking_in_progress_;
+  }
+
+  V8_INLINE bool is_young_generation_enabled() const {
+    return is_young_generation_enabled_;
+  }
+
+  bool is_incremental_marking_in_progress_ = false;
+  bool is_young_generation_enabled_ = false;
+
+  friend class internal::HeapBase;
+  friend class internal::WriteBarrierTypeForCagedHeapPolicy;
+};
+
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_HEAP_HANDLE_H_

include/cppgc/heap.h

@@ -21,6 +21,7 @@
 namespace cppgc {
 
 class AllocationHandle;
+class HeapHandle;
 
 /**
  * Implementation details of cppgc. Those details are considered internal and
@@ -31,11 +32,6 @@ namespace internal {
 class Heap;
 }  // namespace internal
 
-/**
- * Used for additional heap APIs.
- */
-class HeapHandle;
-
 class V8_EXPORT Heap {
  public:
   /**

include/cppgc/internal/api-constants.h

@@ -32,6 +32,12 @@ static constexpr uint16_t kFullyConstructedBitMask = uint16_t{1};
 
 static constexpr size_t kPageSize = size_t{1} << 17;
 
+#if defined(V8_TARGET_ARCH_ARM64) && defined(V8_OS_MACOS)
+constexpr size_t kGuardPageSize = 0;
+#else
+constexpr size_t kGuardPageSize = 4096;
+#endif
+
 static constexpr size_t kLargeObjectSizeThreshold = kPageSize / 2;
 
 #if defined(CPPGC_CAGED_HEAP)

include/cppgc/internal/base-page-handle.h

@@ -0,0 +1,45 @@
+// Copyright 2022 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_INTERNAL_BASE_PAGE_HANDLE_H_
+#define INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_
+
+#include "cppgc/heap-handle.h"
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/logging.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+// The class is needed in the header to allow for fast access to HeapHandle in
+// the write barrier.
+class BasePageHandle {
+ public:
+  static V8_INLINE BasePageHandle* FromPayload(void* payload) {
+    return reinterpret_cast<BasePageHandle*>(
+        (reinterpret_cast<uintptr_t>(payload) &
+         ~(api_constants::kPageSize - 1)) +
+        api_constants::kGuardPageSize);
+  }
+  static V8_INLINE const BasePageHandle* FromPayload(const void* payload) {
+    return FromPayload(const_cast<void*>(payload));
+  }
+
+  HeapHandle& heap_handle() { return heap_handle_; }
+  const HeapHandle& heap_handle() const { return heap_handle_; }
+
+ protected:
+  explicit BasePageHandle(HeapHandle& heap_handle) : heap_handle_(heap_handle) {
+    CPPGC_DCHECK(reinterpret_cast<uintptr_t>(this) % api_constants::kPageSize ==
+                 api_constants::kGuardPageSize);
+  }
+
+  HeapHandle& heap_handle_;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_BASE_PAGE_HANDLE_H_

include/cppgc/internal/caged-heap-local-data.h

@@ -82,12 +82,11 @@ static_assert(sizeof(AgeTable) == 1 * api_constants::kMB,
 
 #endif  // CPPGC_YOUNG_GENERATION
 
+// TODO(v8:12231): Remove this class entirely so that it doesn't occupy space is
+// when CPPGC_YOUNG_GENERATION is off.
 struct CagedHeapLocalData final {
-  CagedHeapLocalData(HeapBase&, PageAllocator&);
+  explicit CagedHeapLocalData(PageAllocator&);
 
-  bool is_incremental_marking_in_progress = false;
-  bool is_young_generation_enabled = false;
-  HeapBase& heap_base;
 #if defined(CPPGC_YOUNG_GENERATION)
   AgeTable age_table;
 #endif

include/cppgc/internal/caged-heap.h

@@ -0,0 +1,41 @@
+// Copyright 2022 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_INTERNAL_CAGED_HEAP_H_
+#define INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_H_
+
+#include <cstddef>
+
+#include "cppgc/internal/api-constants.h"
+#include "cppgc/internal/base-page-handle.h"
+#include "v8config.h"  // NOLINT(build/include_directory)
+
+namespace cppgc {
+namespace internal {
+
+class V8_EXPORT CagedHeapBase {
+ public:
+  V8_INLINE static bool IsWithinNormalPageReservation(uintptr_t heap_base,
+                                                      void* address) {
+    return (reinterpret_cast<uintptr_t>(address) - heap_base) <
+           api_constants::kCagedHeapNormalPageReservationSize;
+  }
+
+  V8_INLINE static BasePageHandle* LookupPageFromInnerPointer(
+      uintptr_t heap_base, void* ptr) {
+    if (V8_LIKELY(IsWithinNormalPageReservation(heap_base, ptr)))
+      return BasePageHandle::FromPayload(ptr);
+    else
+      return LookupLargePageFromInnerPointer(heap_base, ptr);
+  }
+
+ private:
+  static BasePageHandle* LookupLargePageFromInnerPointer(uintptr_t heap_base,
+                                                         void* address);
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // INCLUDE_CPPGC_INTERNAL_CAGED_HEAP_H_

include/cppgc/internal/write-barrier.h

@@ -8,6 +8,7 @@
 #include <cstddef>
 #include <cstdint>
 
+#include "cppgc/heap-handle.h"
 #include "cppgc/heap-state.h"
 #include "cppgc/internal/api-constants.h"
 #include "cppgc/internal/atomic-entry-flag.h"
@@ -18,6 +19,7 @@
 
 #if defined(CPPGC_CAGED_HEAP)
 #include "cppgc/internal/caged-heap-local-data.h"
+#include "cppgc/internal/caged-heap.h"
 #endif
 
 namespace cppgc {
@@ -123,9 +125,11 @@ class V8_EXPORT WriteBarrier final {
   static CagedHeapLocalData& GetLocalData(HeapHandle&);
   static void GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
                                       const AgeTable& age_table,
-                                      const void* slot, uintptr_t value_offset);
+                                      const void* slot, uintptr_t value_offset,
+                                      HeapHandle* heap_handle);
   static void GenerationalBarrierForSourceObjectSlow(
-      const CagedHeapLocalData& local_data, const void* object);
+      const CagedHeapLocalData& local_data, const void* object,
+      HeapHandle* heap_handle);
 #endif  // CPPGC_YOUNG_GENERATION
 
   static AtomicEntryFlag write_barrier_enabled_;
@@ -168,9 +172,17 @@ class V8_EXPORT WriteBarrierTypeForCagedHeapPolicy final {
     if (!TryGetCagedHeap(value, value, params)) {
       return WriteBarrier::Type::kNone;
     }
-    if (V8_UNLIKELY(params.caged_heap().is_incremental_marking_in_progress)) {
+
+    // We know that |value| points either within the normal page or to the
+    // beginning of large-page, so extract the page header by bitmasking.
+    BasePageHandle* page =
+        BasePageHandle::FromPayload(const_cast<void*>(value));
+
+    HeapHandle& heap_handle = page->heap_handle();
+    if (V8_UNLIKELY(heap_handle.is_incremental_marking_in_progress())) {
       return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
     }
+
     return SetAndReturnType<WriteBarrier::Type::kNone>(params);
   }
 
@@ -220,12 +232,17 @@ struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
     const bool within_cage = TryGetCagedHeap(slot, value, params);
     if (!within_cage) return WriteBarrier::Type::kNone;
 
-    const auto& caged_heap = params.caged_heap();
+    // We know that |value| points either within the normal page or to the
-    if (V8_LIKELY(!caged_heap.is_incremental_marking_in_progress)) {
+    // beginning of large-page, so extract the page header by bitmasking.
+    BasePageHandle* page =
+        BasePageHandle::FromPayload(const_cast<void*>(value));
+
+    HeapHandle& heap_handle = page->heap_handle();
+    if (V8_LIKELY(!heap_handle.is_incremental_marking_in_progress())) {
 #if defined(CPPGC_YOUNG_GENERATION)
-      if (!caged_heap.is_young_generation_enabled)
+      if (!heap_handle.is_young_generation_enabled())
         return WriteBarrier::Type::kNone;
-      params.heap = reinterpret_cast<HeapHandle*>(params.start);
+      params.heap = &heap_handle;
       params.slot_offset = reinterpret_cast<uintptr_t>(slot) - params.start;
       params.value_offset = reinterpret_cast<uintptr_t>(value) - params.start;
       return SetAndReturnType<WriteBarrier::Type::kGenerational>(params);
@@ -235,7 +252,7 @@ struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
     }
 
     // Use marking barrier.
-    params.heap = reinterpret_cast<HeapHandle*>(params.start);
+    params.heap = &heap_handle;
     return SetAndReturnType<WriteBarrier::Type::kMarking>(params);
   }
 };
@@ -254,8 +271,9 @@ struct WriteBarrierTypeForCagedHeapPolicy::ValueModeDispatch<
     HeapHandle& handle = callback();
     if (V8_LIKELY(!IsMarking(handle, params))) {
       // params.start is populated by IsMarking().
-      if (!params.caged_heap().is_young_generation_enabled)
+      if (!handle.is_young_generation_enabled()) {
         return WriteBarrier::Type::kNone;
+      }
       params.heap = &handle;
       params.slot_offset = reinterpret_cast<uintptr_t>(slot) - params.start;
       // params.value_offset stays 0.
@@ -417,7 +435,8 @@ void WriteBarrier::GenerationalBarrier(const Params& params, const void* slot) {
   if (V8_LIKELY(age_table.GetAge(params.slot_offset) == AgeTable::Age::kYoung))
     return;
 
-  GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset);
+  GenerationalBarrierSlow(local_data, age_table, slot, params.value_offset,
+                          params.heap);
 }
 
 // static
@@ -433,7 +452,8 @@ void WriteBarrier::GenerationalBarrierForSourceObject(
   if (V8_LIKELY(age_table.GetAge(params.slot_offset) == AgeTable::Age::kYoung))
     return;
 
-  GenerationalBarrierForSourceObjectSlow(local_data, inner_pointer);
+  GenerationalBarrierForSourceObjectSlow(local_data, inner_pointer,
+                                         params.heap);
 }
 
 #endif  // !CPPGC_YOUNG_GENERATION

src/heap/cppgc/caged-heap-local-data.cc

@@ -13,9 +13,7 @@
 namespace cppgc {
 namespace internal {
 
-CagedHeapLocalData::CagedHeapLocalData(HeapBase& heap_base,
+CagedHeapLocalData::CagedHeapLocalData(PageAllocator& allocator) {
-                                       PageAllocator& allocator)
-    : heap_base(heap_base) {
 #if defined(CPPGC_YOUNG_GENERATION)
   age_table.Reset(&allocator);
 #endif  // defined(CPPGC_YOUNG_GENERATION)

src/heap/cppgc/caged-heap.cc

@@ -2,6 +2,10 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "include/cppgc/internal/caged-heap.h"
+
+#include <map>
+
 #include "v8config.h"  // NOLINT(build/include_directory)
 
 #if !defined(CPPGC_CAGED_HEAP)
@@ -12,10 +16,12 @@
 #include "include/cppgc/member.h"
 #include "include/cppgc/platform.h"
 #include "src/base/bounded-page-allocator.h"
+#include "src/base/lazy-instance.h"
 #include "src/base/logging.h"
 #include "src/base/platform/platform.h"
 #include "src/heap/cppgc/caged-heap.h"
 #include "src/heap/cppgc/globals.h"
+#include "src/heap/cppgc/heap-base.h"
 #include "src/heap/cppgc/heap-page.h"
 #include "src/heap/cppgc/member.h"
 
@@ -31,6 +37,15 @@ static_assert(api_constants::kCagedHeapNormalPageReservationSize ==
 
 namespace {
 
+// TODO(v8:12231): Remove once shared cage is there. Currently it's only used
+// for large pages lookup in the write barrier.
+using Cages = std::map<uintptr_t /*cage_base*/, HeapBase*>;
+
+static Cages& global_cages() {
+  static v8::base::LeakyObject<Cages> instance;
+  return *instance.get();
+}
+
 VirtualMemory ReserveCagedHeap(PageAllocator& platform_allocator) {
   DCHECK_EQ(0u,
             kCagedHeapReservationSize % platform_allocator.AllocatePageSize());
@@ -70,8 +85,7 @@ CagedHeap::CagedHeap(HeapBase& heap_base, PageAllocator& platform_allocator)
   // Failing to commit the reservation means that we are out of memory.
   CHECK(is_not_oom);
 
-  new (reserved_area_.address())
+  new (reserved_area_.address()) CagedHeapLocalData(platform_allocator);
-      CagedHeapLocalData(heap_base, platform_allocator);
 
   const CagedAddress caged_heap_start =
       RoundUp(reinterpret_cast<CagedAddress>(reserved_area_.address()) +
@@ -97,6 +111,10 @@ CagedHeap::CagedHeap(HeapBase& heap_base, PageAllocator& platform_allocator)
       kCagedHeapNormalPageReservationSize, kPageSize,
       v8::base::PageInitializationMode::kAllocatedPagesMustBeZeroInitialized,
       v8::base::PageFreeingMode::kMakeInaccessible);
+
+  auto is_inserted = global_cages().emplace(
+      reinterpret_cast<uintptr_t>(reserved_area_.address()), &heap_base);
+  CHECK(is_inserted.second);
 }
 
 CagedHeap::~CagedHeap() {
@@ -107,12 +125,6 @@ CagedHeap::~CagedHeap() {
 #endif  // defined(CPPGC_POINTER_COMPRESSION)
 }
 
-#if defined(CPPGC_YOUNG_GENERATION)
-void CagedHeap::EnableGenerationalGC() {
-  local_data().is_young_generation_enabled = true;
-}
-#endif  // defined(CPPGC_YOUNG_GENERATION)
-
 void CagedHeap::NotifyLargePageCreated(LargePage* page) {
   DCHECK(page);
   auto result = large_pages_.insert(page);
@@ -145,5 +157,16 @@ LargePage* CagedHeap::LookupLargePageFromInnerPointer(void* ptr) const {
   return page;
 }
 
+// static
+BasePageHandle* CagedHeapBase::LookupLargePageFromInnerPointer(
+    uintptr_t heap_base, void* address) {
+  DCHECK_EQ(0, heap_base & (kCagedHeapReservationAlignment - 1));
+
+  auto it = global_cages().find(heap_base);
+  DCHECK_NE(global_cages().end(), it);
+
+  return it->second->caged_heap().LookupLargePageFromInnerPointer(address);
+}
+
 }  // namespace internal
 }  // namespace cppgc

src/heap/cppgc/caged-heap.h

@@ -50,10 +50,6 @@ class CagedHeap final {
   CagedHeap(const CagedHeap&) = delete;
   CagedHeap& operator=(const CagedHeap&) = delete;
 
-#if defined(CPPGC_YOUNG_GENERATION)
-  void EnableGenerationalGC();
-#endif  // defined(CPPGC_YOUNG_GENERATION)
-
   AllocatorType& normal_page_allocator() {
     return *normal_page_bounded_allocator_;
   }
@@ -72,6 +68,7 @@ class CagedHeap final {
   void NotifyLargePageDestroyed(LargePage* page);
 
   BasePage* LookupPageFromInnerPointer(void* ptr) const;
+  LargePage* LookupLargePageFromInnerPointer(void* ptr) const;
 
   CagedHeapLocalData& local_data() {
     return *static_cast<CagedHeapLocalData*>(reserved_area_.address());
@@ -88,8 +85,6 @@ class CagedHeap final {
   void* base() const { return reserved_area_.address(); }
 
  private:
-  LargePage* LookupLargePageFromInnerPointer(void* ptr) const;
-
   const VirtualMemory reserved_area_;
   std::unique_ptr<AllocatorType> normal_page_bounded_allocator_;
   std::unique_ptr<AllocatorType> large_page_bounded_allocator_;

src/heap/cppgc/heap-base.cc

@@ -90,8 +90,7 @@ HeapBase::HeapBase(
 #endif  // defined(CPPGC_YOUNG_GENERATION)
       stack_support_(stack_support),
       marking_support_(marking_support),
-      sweeping_support_(sweeping_support),
+      sweeping_support_(sweeping_support) {
-      generation_support_(GenerationSupport::kSingleGeneration) {
   stats_collector_->RegisterObserver(
       &allocation_observer_for_PROCESS_HEAP_STATISTICS_);
 }
@@ -128,8 +127,7 @@ void HeapBase::EnableGenerationalGC() {
   // Notify the global flag that the write barrier must always be enabled.
   YoungGenerationEnabler::Enable();
   // Enable young generation for the current heap.
-  caged_heap().EnableGenerationalGC();
+  HeapHandle::is_young_generation_enabled_ = true;
-  generation_support_ = GenerationSupport::kYoungAndOldGenerations;
 }
 
 void HeapBase::ResetRememberedSet() {
@@ -174,11 +172,8 @@ void HeapBase::Terminate() {
 
 #if defined(CPPGC_YOUNG_GENERATION)
   if (generational_gc_supported()) {
-    DCHECK(caged_heap().local_data().is_young_generation_enabled);
+    DCHECK(is_young_generation_enabled());
-    DCHECK_EQ(GenerationSupport::kYoungAndOldGenerations, generation_support_);
+    HeapHandle::is_young_generation_enabled_ = false;
-
-    caged_heap().local_data().is_young_generation_enabled = false;
-    generation_support_ = GenerationSupport::kSingleGeneration;
     YoungGenerationEnabler::Disable();
   }
 #endif  // defined(CPPGC_YOUNG_GENERATION)

src/heap/cppgc/heap-base.h

@@ -8,6 +8,7 @@
 #include <memory>
 #include <set>
 
+#include "include/cppgc/heap-handle.h"
 #include "include/cppgc/heap-statistics.h"
 #include "include/cppgc/heap.h"
 #include "include/cppgc/internal/persistent-node.h"
@@ -60,12 +61,6 @@ class OverrideEmbedderStackStateScope;
 
 class Platform;
 
-class V8_EXPORT HeapHandle {
- private:
-  HeapHandle() = default;
-  friend class internal::HeapBase;
-};
-
 namespace internal {
 
 class FatalOutOfMemoryHandler;
@@ -218,8 +213,7 @@ class V8_EXPORT_PRIVATE HeapBase : public cppgc::HeapHandle {
   SweepingType sweeping_support() const { return sweeping_support_; }
 
   bool generational_gc_supported() const {
-    const bool supported =
+    const bool supported = is_young_generation_enabled();
-        (generation_support_ == GenerationSupport::kYoungAndOldGenerations);
 #if defined(CPPGC_YOUNG_GENERATION)
     DCHECK_IMPLIES(supported, YoungGenerationEnabler::IsEnabled());
 #endif  // defined(CPPGC_YOUNG_GENERATION)
@@ -235,12 +229,13 @@ class V8_EXPORT_PRIVATE HeapBase : public cppgc::HeapHandle {
     name_for_unnamed_object_ = value;
   }
 
- protected:
+  void set_incremental_marking_in_progress(bool value) {
-  enum class GenerationSupport : uint8_t {
+    is_incremental_marking_in_progress_ = value;
-    kSingleGeneration,
+  }
-    kYoungAndOldGenerations,
-  };
 
+  using HeapHandle::is_incremental_marking_in_progress;
+
+ protected:
   // Used by the incremental scheduler to finalize a GC if supported.
   virtual void FinalizeIncrementalGarbageCollectionIfNeeded(
       cppgc::Heap::StackState) = 0;
@@ -313,7 +308,6 @@ class V8_EXPORT_PRIVATE HeapBase : public cppgc::HeapHandle {
 
   MarkingType marking_support_;
   SweepingType sweeping_support_;
-  GenerationSupport generation_support_;
 
   HeapObjectNameForUnnamedObject name_for_unnamed_object_ =
       HeapObjectNameForUnnamedObject::kUseHiddenName;

src/heap/cppgc/heap-page.cc

@@ -22,6 +22,8 @@
 namespace cppgc {
 namespace internal {
 
+static_assert(api_constants::kGuardPageSize == kGuardPageSize);
+
 namespace {
 
 Address AlignAddress(Address address, size_t alignment) {
@@ -31,6 +33,10 @@ Address AlignAddress(Address address, size_t alignment) {
 
 }  // namespace
 
+HeapBase& BasePage::heap() const {
+  return static_cast<HeapBase&>(heap_handle_);
+}
+
 // static
 BasePage* BasePage::FromInnerAddress(const HeapBase* heap, void* address) {
   return const_cast<BasePage*>(
@@ -119,10 +125,10 @@ const HeapObjectHeader* BasePage::TryObjectHeaderFromInnerAddress(
 }
 
 BasePage::BasePage(HeapBase& heap, BaseSpace& space, PageType type)
-    : heap_(heap), space_(space), type_(type) {
+    : BasePageHandle(heap), space_(space), type_(type) {
   DCHECK_EQ(0u, (reinterpret_cast<uintptr_t>(this) - kGuardPageSize) &
                     kPageOffsetMask);
-  DCHECK_EQ(&heap_.raw_heap(), space_.raw_heap());
+  DCHECK_EQ(&heap.raw_heap(), space_.raw_heap());
 }
 
 // static

src/heap/cppgc/heap-page.h

@@ -5,6 +5,7 @@
 #ifndef V8_HEAP_CPPGC_HEAP_PAGE_H_
 #define V8_HEAP_CPPGC_HEAP_PAGE_H_
 
+#include "include/cppgc/internal/base-page-handle.h"
 #include "src/base/iterator.h"
 #include "src/base/macros.h"
 #include "src/heap/cppgc/globals.h"
@@ -20,7 +21,7 @@ class LargePageSpace;
 class HeapBase;
 class PageBackend;
 
-class V8_EXPORT_PRIVATE BasePage {
+class V8_EXPORT_PRIVATE BasePage : public BasePageHandle {
  public:
   static inline BasePage* FromPayload(void*);
   static inline const BasePage* FromPayload(const void*);
@@ -33,7 +34,7 @@ class V8_EXPORT_PRIVATE BasePage {
   BasePage(const BasePage&) = delete;
   BasePage& operator=(const BasePage&) = delete;
 
-  HeapBase& heap() const { return heap_; }
+  HeapBase& heap() const;
 
   BaseSpace& space() const { return space_; }
 
@@ -91,7 +92,6 @@ class V8_EXPORT_PRIVATE BasePage {
   BasePage(HeapBase&, BaseSpace&, PageType);
 
  private:
-  HeapBase& heap_;
   BaseSpace& space_;
   PageType type_;
   size_t discarded_memory_ = 0;
@@ -260,16 +260,12 @@ class V8_EXPORT_PRIVATE LargePage final : public BasePage {
 
 // static
 BasePage* BasePage::FromPayload(void* payload) {
-  return reinterpret_cast<BasePage*>(
+  return static_cast<BasePage*>(BasePageHandle::FromPayload(payload));
-      (reinterpret_cast<uintptr_t>(payload) & kPageBaseMask) + kGuardPageSize);
 }
 
 // static
 const BasePage* BasePage::FromPayload(const void* payload) {
-  return reinterpret_cast<const BasePage*>(
+  return static_cast<const BasePage*>(BasePageHandle::FromPayload(payload));
-      (reinterpret_cast<uintptr_t>(const_cast<void*>(payload)) &
-       kPageBaseMask) +
-      kGuardPageSize);
 }
 
 template <AccessMode mode = AccessMode::kNonAtomic>

src/heap/cppgc/marker.cc

@@ -38,9 +38,7 @@ bool EnterIncrementalMarkingIfNeeded(Marker::MarkingConfig config,
       config.marking_type ==
           Marker::MarkingConfig::MarkingType::kIncrementalAndConcurrent) {
     WriteBarrier::FlagUpdater::Enter();
-#if defined(CPPGC_CAGED_HEAP)
+    heap.set_incremental_marking_in_progress(true);
-    heap.caged_heap().local_data().is_incremental_marking_in_progress = true;
-#endif  // defined(CPPGC_CAGED_HEAP)
     return true;
   }
   return false;
@@ -52,9 +50,7 @@ bool ExitIncrementalMarkingIfNeeded(Marker::MarkingConfig config,
       config.marking_type ==
           Marker::MarkingConfig::MarkingType::kIncrementalAndConcurrent) {
     WriteBarrier::FlagUpdater::Exit();
-#if defined(CPPGC_CAGED_HEAP)
+    heap.set_incremental_marking_in_progress(false);
-    heap.caged_heap().local_data().is_incremental_marking_in_progress = false;
-#endif  // defined(CPPGC_CAGED_HEAP)
     return true;
   }
   return false;

src/heap/cppgc/write-barrier.cc

@@ -28,12 +28,7 @@ namespace {
 template <MarkerBase::WriteBarrierType type>
 void ProcessMarkValue(HeapObjectHeader& header, MarkerBase* marker,
                       const void* value) {
-#if defined(CPPGC_CAGED_HEAP)
+  DCHECK(marker->heap().is_incremental_marking_in_progress());
-  DCHECK(reinterpret_cast<CagedHeapLocalData*>(
-             reinterpret_cast<uintptr_t>(value) &
-             ~(kCagedHeapReservationAlignment - 1))
-             ->is_incremental_marking_in_progress);
-#endif
   DCHECK(header.IsMarked<AccessMode::kAtomic>());
   DCHECK(marker);
 
@@ -128,31 +123,39 @@ void WriteBarrier::SteeleMarkingBarrierSlow(const void* value) {
 void WriteBarrier::GenerationalBarrierSlow(const CagedHeapLocalData& local_data,
                                            const AgeTable& age_table,
                                            const void* slot,
-                                           uintptr_t value_offset) {
+                                           uintptr_t value_offset,
+                                           HeapHandle* heap_handle) {
   DCHECK(slot);
+  DCHECK(heap_handle);
+  DCHECK_GT(kCagedHeapReservationSize, value_offset);
   // A write during atomic pause (e.g. pre-finalizer) may trigger the slow path
   // of the barrier. This is a result of the order of bailouts where not marking
   // results in applying the generational barrier.
-  if (local_data.heap_base.in_atomic_pause()) return;
+  auto& heap = HeapBase::From(*heap_handle);
+  if (heap.in_atomic_pause()) return;
 
   if (value_offset > 0 && age_table.GetAge(value_offset) == AgeTable::Age::kOld)
     return;
 
   // Record slot.
-  local_data.heap_base.remembered_set().AddSlot((const_cast<void*>(slot)));
+  heap.remembered_set().AddSlot((const_cast<void*>(slot)));
 }
 
 // static
 void WriteBarrier::GenerationalBarrierForSourceObjectSlow(
-    const CagedHeapLocalData& local_data, const void* inner_pointer) {
+    const CagedHeapLocalData& local_data, const void* inner_pointer,
+    HeapHandle* heap_handle) {
   DCHECK(inner_pointer);
+  DCHECK(heap_handle);
+
+  auto& heap = HeapBase::From(*heap_handle);
 
   auto& object_header =
-      BasePage::FromInnerAddress(&local_data.heap_base, inner_pointer)
+      BasePage::FromInnerAddress(&heap, inner_pointer)
           ->ObjectHeaderFromInnerAddress<AccessMode::kAtomic>(inner_pointer);
 
   // Record the source object.
-  local_data.heap_base.remembered_set().AddSourceObject(
+  heap.remembered_set().AddSourceObject(
       const_cast<HeapObjectHeader&>(object_header));
 }
 #endif  // CPPGC_YOUNG_GENERATION