Fix bug in system allocator

paddle/fluid/memory/detail/system_allocator.cc

@@ -79,7 +79,18 @@ void* GPUAllocator::Alloc(size_t& index, size_t size) {
   // if size is 0.  We just make sure it does.
   if (size <= 0) return nullptr;
   void* p;
+  int prev_id;
+  cudaGetDevice(&prev_id);
+  if (prev_id != gpu_id_) {
+    cudaSetDevice(gpu_id_);
+  }
+
   cudaError_t result = cudaMalloc(&p, size);
+
+  if (prev_id != gpu_id_) {
+    cudaSetDevice(prev_id);
+  }
+
   if (result == cudaSuccess) {
     index = 0;
     gpu_alloc_size_ += size;

paddle/fluid/memory/detail/system_allocator.h

@@ -43,6 +43,8 @@ class CPUAllocator : public SystemAllocator {
 #ifdef PADDLE_WITH_CUDA
 class GPUAllocator : public SystemAllocator {
  public:
+  explicit GPUAllocator(int gpu_id) : gpu_id_(gpu_id) {}
+
   virtual void* Alloc(size_t& index, size_t size);
   virtual void Free(void* p, size_t size, size_t index);
   virtual bool UseGpu() const;
@@ -50,6 +52,7 @@ class GPUAllocator : public SystemAllocator {
  private:
   size_t gpu_alloc_size_ = 0;
   size_t fallback_alloc_size_ = 0;
+  int gpu_id_;
 };
 #endif
 

paddle/fluid/memory/memory.cc

@@ -69,7 +69,7 @@ BuddyAllocator* GetGPUBuddyAllocator(int gpu_id) {
   }
   platform::SetDeviceId(gpu_id);
   if (!as[gpu_id]) {
-    as[gpu_id] = new BuddyAllocator(new detail::GPUAllocator,
+    as[gpu_id] = new BuddyAllocator(new detail::GPUAllocator(gpu_id),
                                     platform::GpuMinChunkSize(),
                                     platform::GpuMaxChunkSize());
     VLOG(10) << "\n\nNOTE: each GPU device use "