ENH: Add useGpu in system allocator

paddle/memory/detail/system_allocator.cc

@@ -60,6 +60,8 @@ void CPUAllocator::Free(void* p, size_t size, size_t index) {
   free(p);
 }
 
+bool CPUAllocator::UseGpu() { return false; }
+
 #ifndef PADDLE_ONLY_CPU
 
 void* GPUAllocator::Alloc(size_t& index, size_t size) {
@@ -131,6 +133,8 @@ void GPUAllocator::Free(void* p, size_t size, size_t index) {
   }
 }
 
+bool GPUAllocator::UseGpu() { return true; }
+
 #endif  // PADDLE_ONLY_CPU
 
 }  // namespace detail

paddle/memory/detail/system_allocator.h

@@ -32,12 +32,14 @@ class SystemAllocator {
   virtual ~SystemAllocator() {}
   virtual void* Alloc(size_t& index, size_t size) = 0;
   virtual void Free(void* p, size_t size, size_t index) = 0;
+  virtual bool UseGpu() = 0;
 };
 
 class CPUAllocator : public SystemAllocator {
  public:
   virtual void* Alloc(size_t& index, size_t size);
   virtual void Free(void* p, size_t size, size_t index);
+  virtual bool UseGpu();
 };
 
 #ifndef PADDLE_ONLY_CPU
@@ -45,7 +47,7 @@ class GPUAllocator : public SystemAllocator {
  public:
   virtual void* Alloc(size_t& index, size_t size);
   virtual void Free(void* p, size_t size, size_t index);
-
+  virtual bool UseGpu();
  private:
   size_t gpu_alloc_size_ = 0;
   size_t fallback_alloc_size_ = 0;