[d8] Use virtual memory to allocate large array buffers.

src/d8.cc

 // Copyright 2012 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 <errno.h>
 #include <stdlib.h>
 #include <string.h>
 #include <sys/stat.h>
 
 #include <algorithm>
@@ skipping 12 matching lines @@
 #include "include/libplatform/libplatform.h"
 #include "include/libplatform/v8-tracing.h"
 #include "src/api.h"
 #include "src/base/cpu.h"
 #include "src/base/debug/stack_trace.h"
 #include "src/base/logging.h"
 #include "src/base/platform/platform.h"
 #include "src/base/sys-info.h"
 #include "src/basic-block-profiler.h"
 #include "src/interpreter/interpreter.h"
+#include "src/msan.h"
 #include "src/snapshot/natives.h"
 #include "src/utils.h"
 #include "src/v8.h"
 
 #ifdef V8_INSPECTOR_ENABLED
 #include "include/v8-inspector.h"
 #endif  // V8_INSPECTOR_ENABLED
 
 #if !defined(_WIN32) && !defined(_WIN64)
 #include <unistd.h>  // NOLINT
@@ skipping 12 matching lines @@
 #define CHECK(condition) assert(condition)
 #endif
 
 namespace v8 {
 
 namespace {
 
 const int MB = 1024 * 1024;
 const int kMaxWorkers = 50;
 
+#define USE_VM 1
+#define VM_THRESHOLD 65536
+// TODO(titzer): allocations should fail if >= 2gb because of
+// array buffers storing the lengths as a SMI internally.
+#define TWO_GB (2u * 1024u * 1024u * 1024u)
 
 class ShellArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
  public:
   virtual void* Allocate(size_t length) {
+#if USE_VM
+    if (RoundToPageSize(&length)) {
+      void* data = VirtualMemoryAllocate(length);
+#if DEBUG
+      // In debug mode, check the memory is zero-initialized.
+      uint8_t* ptr = reinterpret_cast<uint8_t*>(data);
+      for (size_t i = 0; i < length; i++) {
+        DCHECK_EQ(0, ptr[i]);
+      }
+#endif
+      return data;
+    }
+#endif
     void* data = AllocateUninitialized(length);
     return data == NULL ? data : memset(data, 0, length);
   }
-  virtual void* AllocateUninitialized(size_t length) { return malloc(length); }
-  virtual void Free(void* data, size_t) { free(data); }
+  virtual void* AllocateUninitialized(size_t length) {
+#if USE_VM
+    if (RoundToPageSize(&length)) return VirtualMemoryAllocate(length);
+#endif
+    return malloc(length);
+  }
+  virtual void Free(void* data, size_t length) {
+#if USE_VM
+    if (RoundToPageSize(&length)) {
+      base::VirtualMemory::ReleaseRegion(data, length);
+      return;
+    }
+#endif
+    free(data);
+  }
+  // If {length} is at least {VM_THRESHOLD}, round up to next page size
+  // and return {true}. Otherwise return {false}.
+  bool RoundToPageSize(size_t* length) {
+    const size_t kPageSize = base::OS::CommitPageSize();
+    if (*length >= VM_THRESHOLD && *length < TWO_GB) {
+      *length = ((*length + kPageSize - 1) / kPageSize) * kPageSize;
+      return true;
+    }
+    return false;
+  }
+#if USE_VM
+  void* VirtualMemoryAllocate(size_t length) {
+    void* data = base::VirtualMemory::ReserveRegion(length);
+    if (data && !base::VirtualMemory::CommitRegion(data, length, false)) {
+      base::VirtualMemory::ReleaseRegion(data, length);
+      return nullptr;
+    }
+    MSAN_MEMORY_IS_INITIALIZED(data, length);
+    return data;
+  }
+#endif
 };
 
 
 class MockArrayBufferAllocator : public v8::ArrayBuffer::Allocator {
  public:
   void* Allocate(size_t length) override {
     size_t actual_length = length > 10 * MB ? 1 : length;
     void* data = AllocateUninitialized(actual_length);
     return data == NULL ? data : memset(data, 0, actual_length);
   }
@@ skipping 2880 matching lines @@
 }
 
 }  // namespace v8
 
 
 #ifndef GOOGLE3
 int main(int argc, char* argv[]) {
   return v8::Shell::Main(argc, argv);
 }
 #endif