Memory profiling in UnityKim Steen Riber (kim@unity3d.com)

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Who am I?

• Core developer @ Unity• Released games

• LIMBO• Watchmen• Total overdose

• Unity focus areas• CPU performance• Memory optimizations

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Optimizing your game

• FPS• CPU usage (Gamecode, Physics, Skinning, Particles, …)• GPU usage (Drawcalls, Shader usage, Image effects,

…)

• Hickups• Spikes in framerate caused by heavy tasks (e.g.

GC.Collect)• Physics world rebuild due to moved static colliders

• Memory• Maintaining small runtime memory on device• Avoid GC Hickups by reducing memory activity• Leak detection

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Performance

• Unity Profiler (Pro Feature)• CPU • GPU• Memory usage

• New Detailed memory view (Unity 4.1)• Memory reference view (Unity 4.2)

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CPU Profiler

• Cpu time consumption for methods• Mono memory activity• Remote Profiling of you game running on target device• Deep profile (editor only)

• Detailed view, but large overhead, only usable for very small scenes

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Memory Profiler

• Simple and Detailed memory view (Unity 4.1)• Detail view is taken as a snapshot (too expensive for per

frame)• Reference view (Unity 4.2)

• See where an object is referenced – Good for leak hunting

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Memory Profiler

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• Simple memory view• Unity reserves chunks of memory from the

os• Mono allocates from a reserved heap • GfxMemory is an estimate

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Mono vs. Unity Memory

• Managed - Mono• Script objects• Wrappers for

unity objects• Game objects• Assets• Components• …

• Memory is garbage collected

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• Native - Unity internal• Asset data

• Textures• Meshes• Audio• Animation

• Game objects• Engine internals

• Rendering• Particles• Webstreams• Physics• …..

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Mono Memory Internals

• Allocates system heap blocks for allocations• Garbage collector cleans up• Will allocate new heap blocks when needed• Fragmentation can cause new heap blocks

even though memory is not exhausted• Heap blocks are kept in Mono for later use

• Memory can be given back to the system after a while

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Fragmentation

• Memory will get fragmentet if there is a lot of activity

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Mono: 16K System: 64K

Mono: 32K System: 64K

Mono: 32K System: 64K

Mono: 48K System: 128K

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Avoiding Allocations

• Reuse temporary buffers• If buffers for data processing are needed every

frame, allocate the buffer once and reuse

• Allocate pools of reusable objects• Create freelists for objects that are needed often

• Use structs instead of classes• Structs are placed on the stack, while classes uses

the heap

• Don’t use OnGUI• Even empty OnGUI calls are very memory

intensive

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Avoiding Allocations• Use the CPU profiler to identify mono allocations

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Unity Object wrapper

• Some Objects used in scripts have large native backing memory in unity• Memory not freed until Finalizers have run

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WWWDecompression buffer

Compressed file

Decompressed file

Managed Native

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Mono Garbage Collection

• Object goes out of scope

• GC.Collect runs when• Mono exhausts the heap space• Or user calls System.GC.Collect()

• Finalizers• Run on a separate thread

• Unity native memory• Dispose() cleans up internal

memory• Eventually called from finalizer• Manually call Dispose() to

cleanup

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Main thread Finalizer thread

www = null;

new(someclass);//no more heap-> GC.Collect();

www.Dispose();

.....

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Garbage collect and Dispose

Demo

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Assetbundle memory usage

• WebStream• Compressed file• Decompression buffers• Uncompressed file

• Assetbundle• Map of objects and offsets in WebStream

• Instantiated objects• Textures, Meshes, etc.

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Assetbundle memory usage

• WWW www = new WWW(assetbundle_url);• Loads the compressed file into memory• Constructs decompression buffers (8MB per

file)• Decompresses the file into memory• Deallocates the decompression buffers

• One decompression buffer of 8MB is reused and never deallocated

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Assetbundle memory usage

• AssetBundle ab = www.assetBundle;• Loads the map of where objects are in the

webstream• Retains the www WebStream

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WebStream

Tex

Tex

Mesh

AssetBundle

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Assetbundle memory usage

• AssetBundle ab = www.assetBundle;• Loads the map of where objects are in the

webstream• Retains the www WebStream

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WebStream

Tex

Tex

Mesh

AssetBundle

Loaded objects

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Assetbundle memory usage

• Texture2D tex = ab.Load(“MyTex", typeof(Texture2D));• Instantiates a texture from the assetbundle• Uploads the texture to the GPU• On editor a system copy is retained (2x

memory)

• Transferbuffer for the RenderThread will grow to fit the largest Texture or Vertexbuffer (never shrinks)

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Assetbundle memory usage

• Deleting the WebStream• www.Dispose(); // will count down the retain count

• If not called, finalizers will clean the memory eventually

• Deleting the Assetbundle• ab.Unload(false);

• Unloads the map and counts down the www retain count

• ab.Unload(true);• Will also force unload all assets created from the

assetbundle

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Assetbundle memory usage

• Removing the loaded objects from memory• ab.Unload(true)

• Force unload objects loaded by assetbundle

• UnloadUnusedAssets()• Unloads when there are no more references to the object

• Use the memory profiler to find remaining references• In Unity 4.1 a reason why a Object is given• In Unity 4.2 specific scripts or Objects referencing a

given object are shown

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Assetbundle memory usage

• For best memory efficiency do one assetbundle at a time

• If more assetbundles are needed at the same time, load one www object into memory at a time, to reduce decompression buffer usage

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Assetbundle memory usage

Demo

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Conclusions

• Avoid memory activity

• Use the memory profiler to monitor memory usage

• Load one WWW object at a time

• Use Dispose() on objects that derive from IDisposable• Specially if they have a large native memory footprint

• Use UnloadUnusedAssets() to clean up assets

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Questions?

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