Add MemoryCoordinatorImpl

content/browser/memory/memory_coordinator_impl.cc

+// Copyright 2016 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 "content/browser/memory/memory_coordinator_impl.h"
+
+#include "content/browser/memory/memory_monitor.h"
+#include "content/public/common/content_features.h"
+
+namespace content {
+
+namespace {
+
+mojom::MemoryState ToMojomMemoryState(base::MemoryState state) {
+  switch (state) {
+    case base::MemoryState::UNKNOWN:
+      return mojom::MemoryState::UNKNOWN;
+    case base::MemoryState::NORMAL:
+      return mojom::MemoryState::NORMAL;
+    case base::MemoryState::THROTTLED:
+      return mojom::MemoryState::THROTTLED;
+    case base::MemoryState::SUSPENDED:
+      return mojom::MemoryState::SUSPENDED;
+    default:
+      NOTREACHED();
+      return mojom::MemoryState::UNKNOWN;
+  }
+}
+
+}  // namespace
+
+// SingletonTraits for MemoryCoordinator. Returns MemoryCoordinatorImpl
+// as an actual instance.
+struct MemoryCoordinatorSingletonTraits
+    : public base::LeakySingletonTraits<MemoryCoordinator> {
+  static MemoryCoordinator* New() {
+    return new MemoryCoordinatorImpl(CreateMemoryMonitor());
+  }
+};
+
+// static
+MemoryCoordinator* MemoryCoordinator::GetInstance() {
+  if (!base::FeatureList::IsEnabled(features::kMemoryCoordinator))
+    return nullptr;
+  return base::Singleton<MemoryCoordinator,
+                         MemoryCoordinatorSingletonTraits>::get();
+}
+
+MemoryCoordinatorImpl::MemoryCoordinatorImpl(
+    std::unique_ptr<MemoryMonitor> memory_monitor)
+    : memory_monitor_(std::move(memory_monitor)) {
+  DCHECK(memory_monitor_.get());
+  // Set default configuration.
+  // TODO(bashi): Provide a way to change these configuration.
+  config_.pressure_threshold_mb = 0;
+  config_.num_children_until_suspended = 2;
+  config_.minimum_transition_period = base::TimeDelta::FromSeconds(30);
+}
+
+MemoryCoordinatorImpl::~MemoryCoordinatorImpl() {}
+
+void MemoryCoordinatorImpl::OnChildAdded() {
+  UpdateState();
+}
+
+void MemoryCoordinatorImpl::OnChildRemoved() {
+  UpdateState();
+}
+
+void MemoryCoordinatorImpl::UpdateState() {
+  base::TimeTicks now = base::TimeTicks::Now();
+  if (!last_state_change_.is_null() &&
+      now - last_state_change_ < config_.minimum_transition_period)
+    return;
+
+  // TODO(bashi): Come up with a good strategy.
+  // The current strategy is that:
+  //  * There is only one global memory state.
+  //  * When avaiable free memory is below a certain threshold (default to
+  //    zero), enter either THROTTLED or SUSPENDED state based on the number
+  //    of child processes.

[haraken, 2016/09/30 02:29:42]

I'm curious what Chris has in mind, but I'd define the global state as follows:

- NORMAL: MC is taking no action because the memory is under the threshold.
- THROTTLING: MC is in a phase to throttle background renderers until the memory
goes down to the threshold.
- SUSPENDING: MC has throttled all background renderers. MC is in a phase to
suspend background renderers until the memory goes down to the threshold.
- DISCARDING: MC has suspended all background renderers. MC is in a phase to
discard background renderers until the memory goes down to the threshold.

My 2 cents.

+  base::MemoryState previous_state = current_state_;
+  int available = memory_monitor_->GetFreeMemoryUntilCriticalMB();
+  if (available > config_.pressure_threshold_mb) {
+    if (current_state_ != MemoryState::NORMAL) {
+      current_state_ = MemoryState::NORMAL;
+    }
+  } else {
+    if (children().size() <= config_.num_children_until_suspended) {
+      current_state_ = MemoryState::SUSPENDED;
+    } else {
+      current_state_ = MemoryState::THROTTLED;
+    }
+  }
+
+  if (current_state_ != previous_state) {
+    last_state_change_ = now;
+    NotifyStateToClients();
+    NotifyStateToChildren();
+  }
+}
+
+void MemoryCoordinatorImpl::NotifyStateToClients() {
+  // SUSPENDED state may not make sense to the browser process. Use THROTTLED
+  // instead when the global state is SUSPENDED.
+  // TODO(bashi): Maybe worth considering another state for the browser.
+  auto state = current_state_ == MemoryState::SUSPENDED ? MemoryState::THROTTLED
+                                                        : current_state_;
+  base::MemoryCoordinatorClientRegistry::GetInstance()->Notify(state);
+}
+
+void MemoryCoordinatorImpl::NotifyStateToChildren() {
+  // TODO(bashi): Don't send SUSPENDED state to the foreground renderer.
+  for (auto& iter : children()) {
+    auto& child_info = iter.second;
+    mojom::MemoryState state = ToMojomMemoryState(current_state_);
+    child_info.memory_state = state;
+    // TODO(bashi): We shouldn't check these conditions but checking them
+    // otherwise crashes. Find & fix the root cause.
+    if (child_info.handle->child().get() &&
+        child_info.handle->child().is_bound())
+      child_info.handle->child()->OnStateChange(state);
+  }
+}
+
+}  // namespace content