cppgc: Implement simple support for 4GB heap reservation

This CL is an initial attempt to reuse BoundedPageAllocator for cppgc.
The caged 4GB heap is needed for:
- fast implementation of the generational barrier;
- potential pointer compression project for Oilpan.

Bug: chromium:1029379
Change-Id: Idfb0ab92c988e2045d4a0e9746bedf841d66e282
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2215818
Commit-Queue: Anton Bikineev <bikineev@chromium.org>
Reviewed-by: Michael Lippautz <mlippautz@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Omer Katz <omerkatz@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68074}

BUILD.gn

@@ -227,6 +227,9 @@ declare_args() {
   # Enable object names in cppgc for debug purposes.
   cppgc_enable_object_names = false
 
+  # Enable heap reservation of size 4GB. Only possible for 64bit archs.
+  cppgc_enable_caged_heap = v8_current_cpu == "x64" || v8_current_cpu == "arm64"
+
   # Enable V8 heap sandbox experimental feature.
   # Sets -DV8_HEAP_SANDBOX.
   v8_enable_heap_sandbox = ""
@@ -305,6 +308,10 @@ assert(
 assert(!v8_enable_heap_sandbox || v8_enable_pointer_compression,
        "V8 Heap Sandbox requires pointer compression")
 
+assert(!cppgc_enable_caged_heap || v8_current_cpu == "x64" ||
+           v8_current_cpu == "arm64",
+       "CppGC caged heap requires 64bit platforms")
+
 v8_random_seed = "314159265"
 v8_toolset_for_shell = "host"
 
@@ -375,6 +382,9 @@ config("cppgc_base_config") {
   if (cppgc_enable_object_names) {
     defines += [ "CPPGC_SUPPORTS_OBJECT_NAMES" ]
   }
+  if (cppgc_enable_caged_heap) {
+    defines += [ "CPPGC_CAGED_HEAP" ]
+  }
 }
 
 # This config should be applied to code using the libsampler.
@@ -4123,6 +4133,8 @@ v8_source_set("cppgc_base") {
     "src/heap/cppgc/stack.h",
     "src/heap/cppgc/sweeper.cc",
     "src/heap/cppgc/sweeper.h",
+    "src/heap/cppgc/virtual-memory.cc",
+    "src/heap/cppgc/virtual-memory.h",
     "src/heap/cppgc/visitor.cc",
     "src/heap/cppgc/worklist.h",
   ]

src/heap/cppgc/globals.h

@@ -16,6 +16,10 @@ namespace internal {
 using Address = uint8_t*;
 using ConstAddress = const uint8_t*;
 
+constexpr size_t kKB = 1024;
+constexpr size_t kMB = kKB * 1024;
+constexpr size_t kGB = kMB * 1024;
+
 // See 6.7.6 (http://eel.is/c++draft/basic.align) for alignment restrictions. We
 // do not fully support all alignment restrictions (following
 // alignof(std​::​max_­align_­t)) but limit to alignof(double).
@@ -42,6 +46,11 @@ constexpr size_t kLargeObjectSizeThreshold = kPageSize / 2;
 constexpr GCInfoIndex kFreeListGCInfoIndex = 0;
 constexpr size_t kFreeListEntrySize = 2 * sizeof(uintptr_t);
 
+#if defined(CPPGC_CAGED_HEAP)
+constexpr size_t kCagedHeapReservationSize = static_cast<size_t>(4) * kGB;
+constexpr size_t kCagedHeapReservationAlignment = kCagedHeapReservationSize;
+#endif
+
 }  // namespace internal
 }  // namespace cppgc
 

src/heap/cppgc/heap.cc

@@ -6,13 +6,17 @@
 
 #include <memory>
 
+#include "src/base/bounded-page-allocator.h"
+#include "src/base/page-allocator.h"
 #include "src/base/platform/platform.h"
 #include "src/heap/cppgc/heap-object-header-inl.h"
 #include "src/heap/cppgc/heap-object-header.h"
 #include "src/heap/cppgc/heap-page.h"
 #include "src/heap/cppgc/heap-visitor.h"
+#include "src/heap/cppgc/page-memory.h"
 #include "src/heap/cppgc/stack.h"
 #include "src/heap/cppgc/sweeper.h"
+#include "src/heap/cppgc/virtual-memory.h"
 
 namespace cppgc {
 
@@ -77,6 +81,38 @@ class ObjectSizeCounter : private HeapVisitor<ObjectSizeCounter> {
   size_t accumulated_size_ = 0;
 };
 
+#if defined(CPPGC_CAGED_HEAP)
+VirtualMemory ReserveCagedHeap(v8::PageAllocator* platform_allocator) {
+  DCHECK_EQ(0u,
+            kCagedHeapReservationSize % platform_allocator->AllocatePageSize());
+
+  static constexpr size_t kAllocationTries = 4;
+  for (size_t i = 0; i < kAllocationTries; ++i) {
+    void* hint = reinterpret_cast<void*>(RoundDown(
+        reinterpret_cast<uintptr_t>(platform_allocator->GetRandomMmapAddr()),
+        kCagedHeapReservationAlignment));
+
+    VirtualMemory memory(platform_allocator, kCagedHeapReservationSize,
+                         kCagedHeapReservationAlignment, hint);
+    if (memory.IsReserved()) return memory;
+  }
+
+  FATAL("Fatal process out of memory: Failed to reserve memory for caged heap");
+  UNREACHABLE();
+}
+
+std::unique_ptr<v8::base::BoundedPageAllocator> CreateBoundedAllocator(
+    v8::PageAllocator* platform_allocator, void* caged_heap_start) {
+  DCHECK(caged_heap_start);
+
+  auto start = reinterpret_cast<v8::base::BoundedPageAllocator::Address>(
+      caged_heap_start);
+
+  return std::make_unique<v8::base::BoundedPageAllocator>(
+      platform_allocator, start, kCagedHeapReservationSize, kPageSize);
+}
+#endif
+
 }  // namespace
 
 // static
@@ -87,12 +123,20 @@ cppgc::LivenessBroker LivenessBrokerFactory::Create() {
 Heap::Heap(std::shared_ptr<cppgc::Platform> platform, size_t custom_spaces)
     : raw_heap_(this, custom_spaces),
       platform_(std::move(platform)),
+#if defined(CPPGC_CAGED_HEAP)
+      reserved_area_(ReserveCagedHeap(platform_->GetPageAllocator())),
+      bounded_allocator_(CreateBoundedAllocator(platform_->GetPageAllocator(),
+                                                reserved_area_.address())),
+      page_backend_(std::make_unique<PageBackend>(bounded_allocator_.get())),
+#else
       page_backend_(
           std::make_unique<PageBackend>(platform_->GetPageAllocator())),
+#endif
       object_allocator_(&raw_heap_),
       sweeper_(&raw_heap_, platform_.get()),
       stack_(std::make_unique<Stack>(v8::base::Stack::GetStackStart())),
-      prefinalizer_handler_(std::make_unique<PreFinalizerHandler>()) {}
+      prefinalizer_handler_(std::make_unique<PreFinalizerHandler>()) {
+}
 
 Heap::~Heap() {
   NoGCScope no_gc(this);

src/heap/cppgc/heap.h

@@ -21,6 +21,11 @@
 #include "src/heap/cppgc/prefinalizer-handler.h"
 #include "src/heap/cppgc/raw-heap.h"
 #include "src/heap/cppgc/sweeper.h"
+#include "src/heap/cppgc/virtual-memory.h"
+
+#if defined(CPPGC_CAGED_HEAP)
+#include "src/base/bounded-page-allocator.h"
+#endif
 
 namespace cppgc {
 namespace internal {
@@ -128,6 +133,12 @@ class V8_EXPORT_PRIVATE Heap final : public cppgc::Heap {
   RawHeap raw_heap_;
 
   std::shared_ptr<cppgc::Platform> platform_;
+#if defined(CPPGC_CAGED_HEAP)
+  // The order is important: page_backend_ must be destroyed before
+  // reserved_area_ is freed.
+  VirtualMemory reserved_area_;
+  std::unique_ptr<v8::base::BoundedPageAllocator> bounded_allocator_;
+#endif
   std::unique_ptr<PageBackend> page_backend_;
   ObjectAllocator object_allocator_;
   Sweeper sweeper_;

src/heap/cppgc/virtual-memory.cc

+// Copyright 2020 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/virtual-memory.h"
+
+#include "include/cppgc/platform.h"
+#include "src/base/macros.h"
+
+namespace cppgc {
+namespace internal {
+
+VirtualMemory::VirtualMemory(PageAllocator* page_allocator, size_t size,
+                             size_t alignment, void* hint)
+    : page_allocator_(page_allocator) {
+  DCHECK_NOT_NULL(page_allocator);
+  DCHECK(IsAligned(size, page_allocator->CommitPageSize()));
+
+  const size_t page_size = page_allocator_->AllocatePageSize();
+  start_ = page_allocator->AllocatePages(hint, RoundUp(size, page_size),
+                                         RoundUp(alignment, page_size),
+                                         PageAllocator::kNoAccess);
+  if (start_) {
+    size_ = RoundUp(size, page_size);
+  }
+}
+
+VirtualMemory::~VirtualMemory() V8_NOEXCEPT {
+  if (IsReserved()) {
+    page_allocator_->FreePages(start_, size_);
+  }
+}
+
+VirtualMemory::VirtualMemory(VirtualMemory&& other) V8_NOEXCEPT
+    : page_allocator_(std::move(other.page_allocator_)),
+      start_(std::move(other.start_)),
+      size_(std::move(other.size_)) {
+  other.Reset();
+}
+
+VirtualMemory& VirtualMemory::operator=(VirtualMemory&& other) V8_NOEXCEPT {
+  DCHECK(!IsReserved());
+  page_allocator_ = std::move(other.page_allocator_);
+  start_ = std::move(other.start_);
+  size_ = std::move(other.size_);
+  other.Reset();
+  return *this;
+}
+
+void VirtualMemory::Reset() {
+  start_ = nullptr;
+  size_ = 0;
+}
+
+}  // namespace internal
+}  // namespace cppgc

src/heap/cppgc/virtual-memory.h

+// Copyright 2020 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_VIRTUAL_MEMORY_H_
+#define V8_HEAP_CPPGC_VIRTUAL_MEMORY_H_
+
+#include <cstdint>
+
+#include "include/cppgc/platform.h"
+#include "src/base/macros.h"
+
+namespace cppgc {
+namespace internal {
+
+// Represents and controls an area of reserved memory.
+class V8_EXPORT_PRIVATE VirtualMemory {
+ public:
+  // Empty VirtualMemory object, controlling no reserved memory.
+  VirtualMemory() = default;
+
+  // Reserves virtual memory containing an area of the given size that is
+  // aligned per |alignment| rounded up to the |page_allocator|'s allocate page
+  // size. The |size| is aligned with |page_allocator|'s commit page size.
+  VirtualMemory(PageAllocator*, size_t size, size_t alignment,
+                void* hint = nullptr);
+
+  // Releases the reserved memory, if any, controlled by this VirtualMemory
+  // object.
+  ~VirtualMemory() V8_NOEXCEPT;
+
+  VirtualMemory(VirtualMemory&&) V8_NOEXCEPT;
+  VirtualMemory& operator=(VirtualMemory&&) V8_NOEXCEPT;
+
+  // Returns whether the memory has been reserved.
+  bool IsReserved() const { return start_ != nullptr; }
+
+  void* address() const {
+    DCHECK(IsReserved());
+    return start_;
+  }
+
+  size_t size() const {
+    DCHECK(IsReserved());
+    return size_;
+  }
+
+ private:
+  // Resets to the default state.
+  void Reset();
+
+  PageAllocator* page_allocator_ = nullptr;
+  void* start_ = nullptr;
+  size_t size_ = 0;
+};
+
+}  // namespace internal
+}  // namespace cppgc
+
+#endif  // V8_HEAP_CPPGC_VIRTUAL_MEMORY_H_