memory_coordinator: Discard tabs under critical memory condition

content/browser/memory/memory_coordinator_impl.cc

Index: content/browser/memory/memory_coordinator_impl.cc
diff --git a/content/browser/memory/memory_coordinator_impl.cc b/content/browser/memory/memory_coordinator_impl.cc
index de5b783a0a4ecd7febe6b1c62f7aa455f4c0b5cb..ce3eef9abf3864582a1712211b0e4cde473b5e82 100644
--- a/content/browser/memory/memory_coordinator_impl.cc
+++ b/content/browser/memory/memory_coordinator_impl.cc
@@ -27,6 +27,7 @@ using MemoryState = base::MemoryState;
 namespace {
 
 const int kDefaultMinimumTransitionPeriodSeconds = 30;
+const int kDefaultTabDiscardingIntervalSeconds = 5;
 
 mojom::MemoryState ToMojomMemoryState(MemoryState state) {
   switch (state) {
@@ -155,6 +156,11 @@ MemoryCoordinatorImpl::MemoryCoordinatorImpl(
           kDefaultMinimumTransitionPeriodSeconds)) {
   DCHECK(memory_monitor_.get());
   base::MemoryCoordinatorProxy::SetMemoryCoordinator(this);
+
+  tab_discarding_closure_ =
+      base::Bind(&MemoryCoordinatorImpl::DiscardTab, base::Unretained(this));
+  tab_discarding_interval_ =
+      base::TimeDelta::FromSeconds(kDefaultTabDiscardingIntervalSeconds);
 }
 
 MemoryCoordinatorImpl::~MemoryCoordinatorImpl() {
@@ -281,6 +287,7 @@ MemoryState MemoryCoordinatorImpl::GetStateForProcess(
 void MemoryCoordinatorImpl::UpdateConditionIfNeeded(
     MemoryCondition next_condition) {
   DCHECK(CalledOnValidThread());
+
   if (memory_condition_ == next_condition)
     return;
 
@@ -313,15 +320,14 @@ void MemoryCoordinatorImpl::UpdateConditionIfNeeded(
     // Set THROTTLED state to all clients/processes.
     UpdateBrowserStateAndNotifyStateToClients(MemoryState::THROTTLED);
     NotifyStateToChildren(MemoryState::THROTTLED);
-    // Idea: Start discarding tabs.
+    // Start discarding tabs.
+    if (delegate_) {
+      base::ThreadTaskRunnerHandle::Get()->PostTask(FROM_HERE,
+                                                    tab_discarding_closure_);
+    }
   }
 }
 
-void MemoryCoordinatorImpl::DiscardTab() {
-  if (delegate_)
-    delegate_->DiscardTab();
-}
-
 RenderProcessHost* MemoryCoordinatorImpl::GetRenderProcessHost(
     int render_process_id) {
   return RenderProcessHost::FromID(render_process_id);
@@ -441,6 +447,19 @@ void MemoryCoordinatorImpl::NotifyStateToChildren(MemoryState state) {
     SetChildMemoryState(iter.first, state);
 }
 
+void MemoryCoordinatorImpl::DiscardTab() {
+  DCHECK(delegate_);
+  if (memory_condition_ != MemoryCondition::CRITICAL)

[haraken, 2017/03/07 08:04:57]

Don't we need to update the memory condition before reading memory_condition_?

[bashi, 2017/03/07 08:14:08]

Yeah, if we want to use up-to-date condition we would move this logic into
UpdateConditionIfNeeded().

+    return;
+
+  // Keep scheduling tab discarding task while memory condition is CRITICAL.

[haraken, 2017/03/07 08:04:57]

a tab discarding task while the memory condition is CRITICAL

+  bool success = delegate_->DiscardTab();
+  if (success) {
+    base::ThreadTaskRunnerHandle::Get()->PostDelayedTask(

[haraken, 2017/03/07 08:04:57]

Maybe it's nicer to check memory_condition_ again before posting a new task.

[bashi, 2017/03/07 08:14:08]

Maybe, but I guess the cost wouldn't be so different (updating condition
involves syscalls).

+        FROM_HERE, tab_discarding_closure_, tab_discarding_interval_);
+  }
+}
+
 MemoryCoordinatorImpl::ChildInfo::ChildInfo() {}
 
 MemoryCoordinatorImpl::ChildInfo::ChildInfo(const ChildInfo& rhs) {