Do V8 GC ASAP if system memory is pressured

content/renderer/render_thread_impl.cc

Index: content/renderer/render_thread_impl.cc
diff --git a/content/renderer/render_thread_impl.cc b/content/renderer/render_thread_impl.cc
index eac04476f119927570bed7ef371c9c5af490f3a1..46c27b8babd535bb04c8f8d43175b791fc53331e 100644
--- a/content/renderer/render_thread_impl.cc
+++ b/content/renderer/render_thread_impl.cc
@@ -160,7 +160,6 @@
 #include "third_party/skia/include/core/SkGraphics.h"
 #include "ui/base/layout.h"
 #include "ui/base/ui_base_switches.h"
-#include "v8/include/v8.h"
 
 #if defined(OS_ANDROID)
 #include <cpu-features.h>
@@ -348,13 +347,6 @@ void NotifyTimezoneChangeOnThisThread() {
   v8::Date::DateTimeConfigurationChangeNotification(isolate);
 }
 
-void LowMemoryNotificationOnThisThread() {
-  v8::Isolate* isolate = v8::Isolate::GetCurrent();
-  if (!isolate)
-    return;
-  isolate->LowMemoryNotification();
-}
-
 class RenderFrameSetupImpl : public mojom::RenderFrameSetup {
  public:
   explicit RenderFrameSetupImpl(
@@ -802,7 +794,9 @@ void RenderThreadImpl::Init(
 #endif
 
   memory_pressure_listener_.reset(new base::MemoryPressureListener(
-      base::Bind(&RenderThreadImpl::OnMemoryPressure, base::Unretained(this))));
+      base::Bind(&RenderThreadImpl::OnMemoryPressure, base::Unretained(this)),
+      base::Bind(&RenderThreadImpl::OnSyncMemoryPressure,
+                 base::Unretained(this))));
 
   int num_raster_threads = 0;
   std::string string_value =
@@ -1978,6 +1972,7 @@ void RenderThreadImpl::OnCreateNewSharedWorker(
 
 void RenderThreadImpl::OnMemoryPressure(
     base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
+  TRACE_EVENT0("memory","RenderThreadImpl::OnMemoryPressure");
   ReleaseFreeMemory();
 
   // Do not call into blink if it is not initialized.
@@ -1985,19 +1980,6 @@ void RenderThreadImpl::OnMemoryPressure(
     blink::WebMemoryPressureListener::onMemoryPressure(
         static_cast<blink::WebMemoryPressureLevel>(memory_pressure_level));
 
-    if (blink::mainThreadIsolate()) {
-      // Trigger full v8 garbage collection on memory pressure notifications.
-      // This will potentially hang the renderer for a long time, however, when
-      // we receive a memory pressure notification, we might be about to be
-      // killed. Because of the janky hang don't do this to foreground
-      // renderers.
-      if (RendererIsHidden()) {
-        blink::mainThreadIsolate()->LowMemoryNotification();
-        RenderThread::Get()->PostTaskToAllWebWorkers(
-            base::Bind(&LowMemoryNotificationOnThisThread));
-      }
-    }
-
     if (memory_pressure_level ==
         base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) {
       // Purge Skia font cache, by setting it to 0 and then again to the
@@ -2152,4 +2134,37 @@ void RenderThreadImpl::PendingRenderFrameConnect::OnConnectionError() {
   DCHECK_EQ(1u, erased);
 }
 
+void RenderThreadImpl::OnSyncMemoryPressure(
+    base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level) {
+  if (blink::mainThreadIsolate()) {

[esprehn, 2016/04/18 21:57:59]

early return instead of indenting the entire function

[hong.zheng, 2016/04/19 06:27:43]

Done.

+    static_assert(
+        static_cast<v8::MemoryPressureLevel>(
+            base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_NONE) ==

[esprehn, 2016/04/18 21:57:59]

these static_asserts should just be in a block at the top of the file, they
don't need to be inside the function

[hong.zheng, 2016/04/19 06:27:43]

Done.

+                v8::MemoryPressureLevel::kNone, "none level not align");
+    static_assert(
+        static_cast<v8::MemoryPressureLevel>(
+            base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_MODERATE) ==
+                v8::MemoryPressureLevel::kModerate, "moderate level not align");
+    static_assert(
+        static_cast<v8::MemoryPressureLevel>(
+            base::MemoryPressureListener::MEMORY_PRESSURE_LEVEL_CRITICAL) ==
+                v8::MemoryPressureLevel::kCritical, "critical level not align");
+
+    v8::MemoryPressureLevel v8_memory_pressure_level =
+        static_cast<v8::MemoryPressureLevel>(memory_pressure_level);
+
+    if (!RendererIsHidden()) {
+      if (v8_memory_pressure_level == v8::MemoryPressureLevel::kCritical)

[esprehn, 2016/04/18 21:57:58]

combine the if statements, doing:

if (x) {
  if (y)
    // comment
    thing();
}

is very hard to read.

// comment
if (x && y)
  thing();

[hong.zheng, 2016/04/19 06:27:43]

Done.

+        // In order to reduce performance impact, translate critical level to
+        // moderate level for foregroud renderer.
+        v8_memory_pressure_level = v8::MemoryPressureLevel::kModerate;
+    }
+
+    blink::mainThreadIsolate()->MemoryPressureNotification(
+        v8_memory_pressure_level);
+    blink::MemoryPressureNotificationToWorkerThreadIsolates(
+        v8_memory_pressure_level);
+  }
+}
+
 }  // namespace content