ENH: Add buddy allocator draft

paddle/memory/detail/CMakeLists.txt

 if(${WITH_GPU})
-  nv_test(system_allocator_test SRCS system_allocator_test.cc)
+  nv_test(system_allocator_test SRCS system_allocator_test.cc DEPS gflags glog)
 else(${WITH_GPU})
-  cc_test(system_allocator_test SRCS system_allocator_test.cc)
+  cc_test(system_allocator_test SRCS system_allocator_test.cc DEPS gflags glog)
 endif(${WITH_GPU})

paddle/memory/detail/buddy_allocator.h

+/* Copyright (c) 2016 PaddlePaddle Authors. All Rights Reserve.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License. */
+
+#pragma once
+
+#include "paddle/memory/detail/system_allocator.h"
+
+namespace paddle {
+namespace memory {
+namespace detail {
+
+template<typename Allocator>
+class BuddyAllocator {
+  public:
+    // TODO(gangliao): This is a draft, add Buddy Allocator Algorithm soon
+    BuddyAllocator() {}
+    ~BuddyAllocator() {}
+
+  public:
+    void* Alloc(size_t size) {
+        return Allocator::Alloc(size); 
+    }
+    void Free(void*) {
+      // Because all info like size are stored in meta data,
+      // thus it's duplicate if add the parameter `size` in
+      // `Free(void*)` interface.
+    }
+    size_t Used();
+
+  public:
+    BuddyAllocator(const BuddyAllocator&) = delete;
+    BuddyAllocator& operator=(const BuddyAllocator&) = delete;
+
+  private:
+    size_t min_alloc_size_;
+    size_t max_alloc_size_;
+
+  private:
+    std::mutex mutex_;
+};
+
+BuddyAllocator<CPUAllocator>* GetCPUBuddyAllocator() {
+  static BuddyAllocator<CPUAllocator>* a = nullptr;
+  if (a == nullptr) {
+    a = new BuddyAllocator<CPUAllocator>();
+  }
+  return a;
+}
+
+#ifndef PADDLE_ONLY_CPU  // The following code are for CUDA.
+
+BuddyAllocator<GPUAllocator>* GetGPUBuddyAllocator(int gpu_id) {
+  static BuddyAllocator<GPUAllocator>** as = NULL;
+  if (as == NULL) {
+    int gpu_num = platform::GetDeviceCount(); 
+    as = new BuddyAllocator<GPUAllocator>*[gpu_num];
+    for (int gpu = 0; gpu < gpu_num; gpu++) {
+        as[gpu] = new BuddyAllocator<GPUAllocator>();
+    }
+  }
+  return as[gpu_id];
+}
+
+#endif  // PADDLE_ONLY_CPU 
+
+}  // namespace detail
+}  // namespace memory
+}  // namespace paddle