[zone-compr] Initial support for zone pointer compression

* Added GN flag v8_enable_zone_compression.
* AccountingAllocator supports allocation of zone segments via both
  malloc/free and bounded page allocator. The latter implementation is
  known to be not efficient yet. This issue will be addressed in a
  follow-up CLs.
* Add support_compression flag to Zone constructor/instance.

Bug: v8:9923
Change-Id: I12ee2d85267dd16f455b1b47edc425dc90c57bcf
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2308345
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#69035}

BUILD.gn

@@ -262,6 +262,10 @@ declare_args() {
   # Enable young generation in cppgc.
   cppgc_enable_young_generation = false
 
+  # Enable V8 zone compression experimental feature.
+  # Sets -DV8_COMPRESS_ZONES.
+  v8_enable_zone_compression = ""
+
   # Enable V8 heap sandbox experimental feature.
   # Sets -DV8_HEAP_SANDBOX.
   v8_enable_heap_sandbox = ""
@@ -304,6 +308,9 @@ if (v8_enable_pointer_compression == "") {
 if (v8_enable_fast_torque == "") {
   v8_enable_fast_torque = v8_enable_fast_mksnapshot
 }
+if (v8_enable_zone_compression == "") {
+  v8_enable_zone_compression = false
+}
 if (v8_enable_heap_sandbox == "") {
   v8_enable_heap_sandbox = false
 }
@@ -476,6 +483,9 @@ config("v8_header_features") {
   if (v8_enable_pointer_compression || v8_enable_31bit_smis_on_64bit_arch) {
     defines += [ "V8_31BIT_SMIS_ON_64BIT_ARCH" ]
   }
+  if (v8_enable_zone_compression) {
+    defines += [ "V8_COMPRESS_ZONES" ]
+  }
   if (v8_enable_heap_sandbox) {
     defines += [ "V8_HEAP_SANDBOX" ]
   }

src/zone/accounting-allocator.cc

@@ -4,17 +4,83 @@
 
 #include "src/zone/accounting-allocator.h"
 
+#include <memory>
+
+#include "src/base/bounded-page-allocator.h"
 #include "src/base/logging.h"
+#include "src/base/macros.h"
 #include "src/utils/allocation.h"
+#include "src/zone/zone-fwd.h"
 #include "src/zone/zone-segment.h"
 
 namespace v8 {
 namespace internal {
 
+namespace {
+
+static constexpr size_t kZonePageSize = 256 * KB;
+
+VirtualMemory ReserveAddressSpace(v8::PageAllocator* platform_allocator) {
+  DCHECK(
+      IsAligned(kZoneReservationSize, platform_allocator->AllocatePageSize()));
+
+  void* hint = reinterpret_cast<void*>(RoundDown(
+      reinterpret_cast<uintptr_t>(platform_allocator->GetRandomMmapAddr()),
+      kZoneReservationAlignment));
+
+  VirtualMemory memory(platform_allocator, kZoneReservationSize, hint,
+                       kZoneReservationAlignment);
+  if (memory.IsReserved()) {
+    CHECK(IsAligned(memory.address(), kZoneReservationAlignment));
+    return memory;
+  }
+
+  FATAL(
+      "Fatal process out of memory: Failed to reserve memory for compressed "
+      "zones");
+  UNREACHABLE();
+}
+
+std::unique_ptr<v8::base::BoundedPageAllocator> CreateBoundedAllocator(
+    v8::PageAllocator* platform_allocator, Address reservation_start) {
+  DCHECK(reservation_start);
+
+  auto allocator = std::make_unique<v8::base::BoundedPageAllocator>(
+      platform_allocator, reservation_start, kZoneReservationSize,
+      kZonePageSize);
+
+  // Exclude first page from allocation to ensure that accesses through
+  // decompressed null pointer will seg-fault.
+  allocator->AllocatePagesAt(reservation_start, kZonePageSize,
+                             v8::PageAllocator::kNoAccess);
+  return allocator;
+}
+
+}  // namespace
+
+AccountingAllocator::AccountingAllocator() {
+  if (COMPRESS_ZONES_BOOL) {
+    v8::PageAllocator* platform_page_allocator = GetPlatformPageAllocator();
+    VirtualMemory memory = ReserveAddressSpace(platform_page_allocator);
+    reserved_area_ = std::make_unique<VirtualMemory>(std::move(memory));
+    bounded_page_allocator_ = CreateBoundedAllocator(platform_page_allocator,
+                                                     reserved_area_->address());
+  }
+}
+
 AccountingAllocator::~AccountingAllocator() = default;
 
-Segment* AccountingAllocator::AllocateSegment(size_t bytes) {
-  void* memory = AllocWithRetry(bytes);
+Segment* AccountingAllocator::AllocateSegment(size_t bytes,
+                                              bool supports_compression) {
+  void* memory;
+  if (COMPRESS_ZONES_BOOL && supports_compression) {
+    bytes = RoundUp(bytes, kZonePageSize);
+    memory = AllocatePages(bounded_page_allocator_.get(), nullptr, bytes,
+                           kZonePageSize, PageAllocator::kReadWrite);
+
+  } else {
+    memory = AllocWithRetry(bytes);
+  }
   if (memory == nullptr) return nullptr;
 
   size_t current =
@@ -28,12 +94,18 @@ Segment* AccountingAllocator::AllocateSegment(size_t bytes) {
   return new (memory) Segment(bytes);
 }
 
-void AccountingAllocator::ReturnSegment(Segment* segment) {
+void AccountingAllocator::ReturnSegment(Segment* segment,
+                                        bool supports_compression) {
   segment->ZapContents();
-  current_memory_usage_.fetch_sub(segment->total_size(),
-                                  std::memory_order_relaxed);
+  size_t segment_size = segment->total_size();
+  current_memory_usage_.fetch_sub(segment_size, std::memory_order_relaxed);
   segment->ZapHeader();
-  free(segment);
+  if (COMPRESS_ZONES_BOOL && supports_compression) {
+    CHECK(FreePages(bounded_page_allocator_.get(), segment, segment_size));
+
+  } else {
+    free(segment);
+  }
 }
 
 }  // namespace internal

src/zone/accounting-allocator.h

@@ -6,27 +6,34 @@
 #define V8_ZONE_ACCOUNTING_ALLOCATOR_H_
 
 #include <atomic>
+#include <memory>
 
 #include "src/base/macros.h"
 #include "src/logging/tracing-flags.h"
 
 namespace v8 {
+
+namespace base {
+class BoundedPageAllocator;
+}
+
 namespace internal {
 
 class Segment;
+class VirtualMemory;
 class Zone;
 
 class V8_EXPORT_PRIVATE AccountingAllocator {
  public:
-  AccountingAllocator() = default;
+  AccountingAllocator();
   virtual ~AccountingAllocator();
 
   // Allocates a new segment. Returns nullptr on failed allocation.
-  Segment* AllocateSegment(size_t bytes);
+  Segment* AllocateSegment(size_t bytes, bool supports_compression);
 
   // Return unneeded segments to either insert them into the pool or release
   // them if the pool is already full or memory pressure is high.
-  void ReturnSegment(Segment* memory);
+  void ReturnSegment(Segment* memory, bool supports_compression);
 
   size_t GetCurrentMemoryUsage() const {
     return current_memory_usage_.load(std::memory_order_relaxed);
@@ -60,6 +67,9 @@ class V8_EXPORT_PRIVATE AccountingAllocator {
   std::atomic<size_t> current_memory_usage_{0};
   std::atomic<size_t> max_memory_usage_{0};
 
+  std::unique_ptr<VirtualMemory> reserved_area_;
+  std::unique_ptr<base::BoundedPageAllocator> bounded_page_allocator_;
+
   DISALLOW_COPY_AND_ASSIGN(AccountingAllocator);
 };
 

src/zone/zone-fwd.h

@@ -5,6 +5,8 @@
 #ifndef V8_ZONE_ZONE_FWD_H_
 #define V8_ZONE_ZONE_FWD_H_
 
+#include "src/common/globals.h"
+
 namespace v8 {
 namespace internal {
 
@@ -23,6 +25,20 @@ class ZoneList;
 template <typename T>
 using ZonePtrList = ZoneList<T*>;
 
+#ifdef V8_COMPRESS_ZONES
+static_assert(kSystemPointerSize == 8,
+              "Zone compression requires 64-bit architectures");
+#define COMPRESS_ZONES_BOOL true
+constexpr size_t kZoneReservationSize = static_cast<size_t>(2) * GB;
+constexpr size_t kZoneReservationAlignment = static_cast<size_t>(4) * GB;
+
+#else  // V8_COMPRESS_ZONES
+#define COMPRESS_ZONES_BOOL false
+// These constants must not be used when zone compression is not enabled.
+constexpr size_t kZoneReservationSize = 1;
+constexpr size_t kZoneReservationAlignment = 1;
+#endif  // V8_COMPRESS_ZONES
+
 }  // namespace internal
 }  // namespace v8
 

src/zone/zone.cc

@@ -29,8 +29,11 @@ constexpr size_t kASanRedzoneBytes = 0;
 
 }  // namespace
 
-Zone::Zone(AccountingAllocator* allocator, const char* name)
-    : allocator_(allocator), name_(name) {
+Zone::Zone(AccountingAllocator* allocator, const char* name,
+           bool support_compression)
+    : allocator_(allocator),
+      name_(name),
+      supports_compression_(support_compression) {
   allocator_->TraceZoneCreation(this);
 }
 
@@ -93,7 +96,7 @@ void Zone::DeleteAll() {
                                 current->capacity());
 
     segment_bytes_allocated_ -= size;
-    allocator_->ReturnSegment(current);
+    allocator_->ReturnSegment(current, supports_compression());
     current = next;
   }
 
@@ -138,8 +141,8 @@ Address Zone::NewExpand(size_t size) {
     V8::FatalProcessOutOfMemory(nullptr, "Zone");
     return kNullAddress;
   }
-
-  Segment* segment = allocator_->AllocateSegment(new_size);
+  Segment* segment =
+      allocator_->AllocateSegment(new_size, supports_compression());
   if (segment == nullptr) {
     V8::FatalProcessOutOfMemory(nullptr, "Zone");
     return kNullAddress;

src/zone/zone.h

@@ -11,6 +11,7 @@
 #include "src/common/globals.h"
 #include "src/zone/accounting-allocator.h"
 #include "src/zone/type-stats.h"
+#include "src/zone/zone-fwd.h"
 #include "src/zone/zone-segment.h"
 
 #ifndef ZONE_NAME
@@ -37,9 +38,15 @@ namespace internal {
 
 class V8_EXPORT_PRIVATE Zone final {
  public:
-  Zone(AccountingAllocator* allocator, const char* name);
+  Zone(AccountingAllocator* allocator, const char* name,
+       bool support_compression = false);
   ~Zone();
 
+  // Returns true if the zone supports zone pointer compression.
+  bool supports_compression() const {
+    return COMPRESS_ZONES_BOOL && supports_compression_;
+  }
+
   // Allocate 'size' bytes of uninitialized memory in the Zone; expands the Zone
   // by allocating new segments of memory on demand using AccountingAllocator
   // (see AccountingAllocator::AllocateSegment()).
@@ -208,6 +215,7 @@ class V8_EXPORT_PRIVATE Zone final {
 
   Segment* segment_head_ = nullptr;
   const char* name_;
+  const bool supports_compression_;
   bool sealed_ = false;
 
 #ifdef V8_ENABLE_PRECISE_ZONE_STATS

test/cctest/test-allocation.cc

@@ -99,8 +99,9 @@ TEST(AccountingAllocatorOOM) {
   AllocationPlatform platform;
   v8::internal::AccountingAllocator allocator;
   CHECK(!platform.oom_callback_called);
+  const bool support_compression = false;
   v8::internal::Segment* result =
-      allocator.AllocateSegment(GetHugeMemoryAmount());
+      allocator.AllocateSegment(GetHugeMemoryAmount(), support_compression);
   // On a few systems, allocation somehow succeeds.
   CHECK_EQ(result == nullptr, platform.oom_callback_called);
 }
@@ -110,12 +111,13 @@ TEST(AccountingAllocatorCurrentAndMax) {
   v8::internal::AccountingAllocator allocator;
   static constexpr size_t kAllocationSizes[] = {51, 231, 27};
   std::vector<v8::internal::Segment*> segments;
+  const bool support_compression = false;
   CHECK_EQ(0, allocator.GetCurrentMemoryUsage());
   CHECK_EQ(0, allocator.GetMaxMemoryUsage());
   size_t expected_current = 0;
   size_t expected_max = 0;
   for (size_t size : kAllocationSizes) {
-    segments.push_back(allocator.AllocateSegment(size));
+    segments.push_back(allocator.AllocateSegment(size, support_compression));
     CHECK_NOT_NULL(segments.back());
     CHECK_EQ(size, segments.back()->total_size());
     expected_current += size;
@@ -125,7 +127,7 @@ TEST(AccountingAllocatorCurrentAndMax) {
   }
   for (auto* segment : segments) {
     expected_current -= segment->total_size();
-    allocator.ReturnSegment(segment);
+    allocator.ReturnSegment(segment, support_compression);
     CHECK_EQ(expected_current, allocator.GetCurrentMemoryUsage());
   }
   CHECK_EQ(expected_max, allocator.GetMaxMemoryUsage());