base: Fix parsing and add dalvik-heap-limit

ui/gl/gl_context_android.cc

 // Copyright (c) 2012 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 "ui/gl/gl_context.h"
 
 #include "base/logging.h"
 #include "base/memory/ref_counted.h"
+#include "base/sys_info.h"
 #include "ui/gl/gl_bindings.h"
 #include "ui/gl/gl_context_egl.h"
 #include "ui/gl/gl_context_stub.h"
 #include "ui/gl/gl_implementation.h"
 #include "ui/gl/gl_surface.h"
 
+
 namespace gfx {
 
 // static
 scoped_refptr<GLContext> GLContext::CreateGLContext(
     GLShareGroup* share_group,
     GLSurface* compatible_surface,
     GpuPreference gpu_preference) {
   if (GetGLImplementation() == kGLImplementationMockGL)
     return scoped_refptr<GLContext>(new GLContextStub());
 
   scoped_refptr<GLContext> context;
   if (compatible_surface->GetHandle())
     context = new GLContextEGL(share_group);
   else
     context = new GLContextStub();
   if (!context->Initialize(compatible_surface, gpu_preference))
     return NULL;
   return context;
 }
 
+bool GLContextEGL::GetTotalGpuMemory(size_t* bytes) {
+  DCHECK(bytes);
+  *bytes = 0;
+
+  // We can't query available GPU memory from the system on Android,
+  // but the dalvik heap size give us a good estimate of available
+  // GPU memory on a wide range of devices.
+  //
+  // The heap size tends to be about 1/4 of total ram on higher end
+  // devices, so we use 1/2 of that by default. For example both the
+  // Nexus 4/10 have 2GB of ram and 512MB Dalvik heap size. For lower
+  // end devices, 1/2 of the heap size can be too high, but this
+  // correlates well with having a small heap-growth-limit. So for
+  // devices with less ram, we factor in the growth limit.
+  //
+  // This is the result of the calculation below:
+  // Droid DNA 1080P  128MB
+  // Nexus S           56MB
+  // Galaxy Nexus     112MB
+  // Nexus 4/10       256MB
+  // Xoom              88MB
+
+  static uint64 dalvik_limit = 0;
+  if (!dalvik_limit) {
+    uint64 heap_size   = base::SysInfo::DalvikHeapSizeMB();

[jar (doing other things), 2013/02/14 01:48:41]

Why are we using uint64 here?  The range of the function should be 32 to 1024,
so there should be no need for such a large value.

[epenner, 2013/02/14 04:18:36]

I think the uint64 crept in from the other code. However the return value is
size_t, and size_t is usually a 64 bit unsigned integer on 32/64 bit systems. I
think the best thing will just be to use *only* size_t and do
static_cast<size_t>(base::SysInfo::DalvikHeapSizeMB()).

+    uint64 heap_growth = base::SysInfo::DalvikHeapGrowthLimitMB();
+    uint64 limit = 0;
+
+    if (heap_size >= 350)
+        limit = heap_size / 2;
+    else
+        limit = (heap_size + (heap_growth * 2)) / 4;
+
+    dalvik_limit = limit * 1024 * 1024;
+  }
+
+  *bytes = dalvik_limit;

[jar (doing other things), 2013/02/14 01:48:41]

I'm surprised this assignment didn't generate a compiler warning when a uint64
into a size_t on a 32 bit platform.  Is that warning disabled?  Am I
misunderstanding context?

I turns out that limit will always be less than or equal to 1024, so
davlik_limit will always be less than 2^30, and fit nicely into an int (and we'd
avoid this more questionable code).  

[epenner, 2013/02/14 04:18:36]

See above, I think size_t is uint64 on both 32/64 bit systems, but I'll change
everything to size_t given that's what this function expects as output.

+  return true;
 }
+
+}