How to build mobile inference library with minimum size

README.md

@@ -7,7 +7,7 @@ Here mainly describes how to deploy PaddlePaddle to the mobile end, as well as s
 - Build PaddlePaddle for IOS
 - [Build PaddlePaddle for Raspberry Pi3](https://github.com/PaddlePaddle/Paddle/blob/develop/doc/howto/cross_compiling/cross_compiling_for_raspberry_cn.md)
 - Build PaddlePaddle for PX2
-- How to build PaddlePaddle mobile inference library with minimum size.
+- [How to build PaddlePaddle mobile inference library with minimum size.](./deployment/build_for_minimum_size.md)
 
 ## Demo
 - [An inference demo program based on the Paddle C API.](./benchmark/tool/C/README.md)

deployment/build_for_minimum_size.md

@@ -0,0 +1,27 @@
+# Build mobile inference library with minimum size
+
+In the mobile application, there usually are some limitations to the size of an executable file.
+Here we explore how to compile the inference library for minimum size.
+
+**Note:**  
+In the original PaddlePaddle, all computationally relevant code is implemented in Matrix.cpp and BaseMatrix.cu, 
+this causes the large compiled Matrix.o and BaseMatrix.o files which can not be split.
+The module of Layer can be split, but the Layer forward and backward computing is included in the same file.
+The configuration definition in proto is redundant. These all will lead to the size of inference library larger.
+
+The new PaddlePaddle is being refactored, the calculation is based on Operator, the configuration description in proto is simplified.
+These will bring a good optimization to the inference library size.
+
+## How to build with minimum size
+Here we mainly introduce some optimization in the compilation process to reduce the size of the inference library. These methods are also used in the refactored PaddlePaddle.
+
+- Compile the code with `-Os` option: By specifying the build type(CMAKE_BUILD_TYPE) to MinSizeRel, the `-Os` option is used by the compiler during the build for minimum size code.
+- Use protobuf-lite instead of protobuf: With the `--cpp_out lite` option, the generated proto configuration rely on MessageLite instead of Message,
+so only libprotobuf-lite is needed for the link, and the size of the final executable file can be reduced.
+- Use `--whole-archive` link option: In `libpaddle_capi_layers.a` contains all the object file of the layers, need use the `--whole-archive` option to ensure that all layers be linked to the executable file.
+But don't forget to use `-no-whole-archive` after `libpaddle_capi_layers.a`, avoid this option affect other libraries.
+[Here's an example](https://github.com/PaddlePaddle/Mobile/blob/develop/benchmark/tool/C/CMakeLists.txt#L41)
+- Remove useless symbols in the shared library: When building a shared library by `libpaddle_capi_layers.a` and `libpaddle_capi_engine.a`,
+you can remove the useless export symbols with the `--version-script` option to reduce the size of the `.dynsym` and `.dynstr` sections.
+[Here's an example](https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/capi/CMakeLists.txt#L61)
+