Update from chromium https://crrev.com/301315

base/memory/discardable_memory_shmem.cc

+// Copyright 2014 The Chromium 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 "base/memory/discardable_memory_shmem.h"
+
+#include "base/lazy_instance.h"
+#include "base/memory/discardable_memory_shmem_allocator.h"
+#include "base/memory/discardable_shared_memory.h"
+
+namespace base {
+namespace {
+
+// Have the DiscardableMemoryManager trigger in-process eviction
+// when address space usage gets too high (e.g. 512 MBytes).
+const size_t kMemoryLimit = 512 * 1024 * 1024;
+
+// internal::DiscardableMemoryManager has an explicit constructor that takes
+// a number of memory limit parameters. The LeakyLazyInstanceTraits doesn't
+// handle the case. Thus, we need our own class here.
+struct DiscardableMemoryManagerLazyInstanceTraits {
+  // Leaky as discardable memory clients can use this after the exit handler
+  // has been called.
+  static const bool kRegisterOnExit = false;
+#ifndef NDEBUG
+  static const bool kAllowedToAccessOnNonjoinableThread = true;
+#endif
+
+  static internal::DiscardableMemoryManager* New(void* instance) {
+    return new (instance) internal::DiscardableMemoryManager(
+        kMemoryLimit, kMemoryLimit, TimeDelta::Max());
+  }
+  static void Delete(internal::DiscardableMemoryManager* instance) {
+    instance->~DiscardableMemoryManager();
+  }
+};
+
+LazyInstance<internal::DiscardableMemoryManager,
+             DiscardableMemoryManagerLazyInstanceTraits> g_manager =
+    LAZY_INSTANCE_INITIALIZER;
+
+}  // namespace
+
+namespace internal {
+
+DiscardableMemoryShmem::DiscardableMemoryShmem(size_t bytes)
+    : bytes_(bytes), is_locked_(false) {
+  g_manager.Pointer()->Register(this, bytes);
+}
+
+DiscardableMemoryShmem::~DiscardableMemoryShmem() {
+  if (is_locked_)
+    Unlock();
+  g_manager.Pointer()->Unregister(this);
+}
+
+// static
+void DiscardableMemoryShmem::ReleaseFreeMemory() {
+  g_manager.Pointer()->ReleaseFreeMemory();
+}
+
+// static
+void DiscardableMemoryShmem::PurgeForTesting() {
+  g_manager.Pointer()->PurgeAll();
+}
+
+bool DiscardableMemoryShmem::Initialize() {
+  return Lock() != DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
+}
+
+DiscardableMemoryLockStatus DiscardableMemoryShmem::Lock() {
+  DCHECK(!is_locked_);
+
+  bool purged = false;
+  if (!g_manager.Pointer()->AcquireLock(this, &purged))
+    return DISCARDABLE_MEMORY_LOCK_STATUS_FAILED;
+
+  is_locked_ = true;
+  return purged ? DISCARDABLE_MEMORY_LOCK_STATUS_PURGED
+                : DISCARDABLE_MEMORY_LOCK_STATUS_SUCCESS;
+}
+
+void DiscardableMemoryShmem::Unlock() {
+  DCHECK(is_locked_);
+  g_manager.Pointer()->ReleaseLock(this);
+  is_locked_ = false;
+}
+
+void* DiscardableMemoryShmem::Memory() const {
+  DCHECK(is_locked_);
+  DCHECK(shared_memory_);
+  return shared_memory_->memory();
+}
+
+bool DiscardableMemoryShmem::AllocateAndAcquireLock() {
+  if (shared_memory_ && shared_memory_->Lock())
+    return true;
+
+  // TODO(reveman): Allocate fixed size memory segments and use a free list to
+  // improve performance and limit the number of file descriptors used.
+  shared_memory_ = DiscardableMemoryShmemAllocator::GetInstance()
+                       ->AllocateLockedDiscardableSharedMemory(bytes_);
+  DCHECK(shared_memory_);
+  return false;
+}
+
+void DiscardableMemoryShmem::ReleaseLock() {
+  shared_memory_->Unlock();
+}
+
+void DiscardableMemoryShmem::Purge() {
+  shared_memory_->Purge(Time());
+  shared_memory_.reset();
+}
+
+bool DiscardableMemoryShmem::IsMemoryResident() const {
+  return shared_memory_->IsMemoryResident();
+}
+
+}  // namespace internal
+}  // namespace base