Limit the number of accelerated canvases that can exist in a render process

third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp

Index: third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
index ceebfd501035a0a9f250aa662cfd7ee32b70fdf8..54d9bc4942cae9d26ac0649b79cd36cd4ab6ef13 100644
--- a/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLCanvasElement.cpp
@@ -89,6 +89,14 @@ const int MaxCanvasArea = 32768 * 8192; // Maximum canvas area in CSS pixels
 // In Skia, we will also limit width/height to 32767.
 const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 
+#if OS(ANDROID)
+// We estimate that the max limit for android phones is a quarter of that for
+// desktops based on local experimental results on Android One.
+const int MaxGlobalAcceleratedImageBufferCount = 20;
+#else
+const int MaxGlobalAcceleratedImageBufferCount = 80;
+#endif
+
 // We estimate the max limit of GPU allocated memory for canvases before Chrome
 // becomes laggy by setting the total allocated memory for accelerated canvases
 // to be equivalent to memory used by 80 accelerated canvases, each has a size
@@ -96,13 +104,7 @@ const int MaxSkiaDim = 32767; // Maximum width/height in CSS pixels.
 // Each such canvas occupies 4000000 = 1000 * 500 * 2 * 4 bytes, where 2 is the
 // gpuBufferCount in ImageBuffer::updateGPUMemoryUsage() and 4 means four bytes
 // per pixel per buffer.
-#if !OS(ANDROID)
-const int MaxGlobalGPUMemoryUsage = 4000000 * 80;
-#else
-// We estimate that the max limit for android phones is a quarter of that for
-// desktops based on local experimental results on Android One.,
-const int MaxGlobalGPUMemoryUsage = 4000000 * 20;
-#endif
+const int MaxGlobalGPUMemoryUsage = 4000000 * MaxGlobalAcceleratedImageBufferCount;
 
 // A default value of quality argument for toDataURL and toBlob
 // It is in an invalid range (outside 0.0 - 1.0) so that it will not be
@@ -555,7 +557,7 @@ const AtomicString HTMLCanvasElement::imageSourceURL() const
 
 void HTMLCanvasElement::prepareSurfaceForPaintingIfNeeded() const
 {
-    ASSERT(m_context && m_context->is2d()); // This function is called by the 2d context
+    DCHECK(m_context && m_context->is2d()); // This function is called by the 2d context
     if (buffer())
         m_imageBuffer->prepareSurfaceForPaintingIfNeeded();
 }
@@ -748,6 +750,13 @@ bool HTMLCanvasElement::shouldAccelerate(const IntSize& size) const
     if (ImageBuffer::getGlobalGPUMemoryUsage() >= MaxGlobalGPUMemoryUsage)
         return false;
 
+    // When GPU allocated memory runs low (due to having created too many

[xlai (Olivia), 2016/06/15 18:54:06]

Hmmm...duplicate comments?

[Justin Novosad, 2016/06/15 19:17:34]

Done.

+    // accelerated canvases), the compositor starves and browser becomes laggy.
+    // Thus, we should stop allocating more GPU memory to new canvases created
+    // when the current memory usage exceeds the threshold.
+    if (ImageBuffer::getGlobalAcceleratedImageBufferCount() >= MaxGlobalAcceleratedImageBufferCount)
+        return false;
+
     return true;
 }
 
@@ -1081,7 +1090,7 @@ IntSize HTMLCanvasElement::bitmapSourceSize() const
 
 ScriptPromise HTMLCanvasElement::createImageBitmap(ScriptState* scriptState, EventTarget& eventTarget, int sx, int sy, int sw, int sh, const ImageBitmapOptions& options, ExceptionState& exceptionState)
 {
-    ASSERT(eventTarget.toLocalDOMWindow());
+    DCHECK(eventTarget.toLocalDOMWindow());
     if (!sw || !sh) {
         exceptionState.throwDOMException(IndexSizeError, String::format("The source %s provided is 0.", sw ? "height" : "width"));
         return ScriptPromise();