SyncedMemory::set_cpu_data and set_gpu_data

[dongfangduoshou123]

void SyncedMemory::set_cpu_data(void* data) {
  check_device();
  CHECK(data);
  if (own_cpu_data_) {
    CaffeFreeHost(cpu_ptr_, cpu_malloc_use_cuda_);
  }
  cpu_ptr_ = data;
  head_ = HEAD_AT_CPU;
  own_cpu_data_ = false;
}

void SyncedMemory::set_gpu_data(void* data) {
  check_device();
#ifndef CPU_ONLY
  CHECK(data);
  if (own_gpu_data_) {
    CUDA_CHECK(cudaFree(gpu_ptr_));
  }
  gpu_ptr_ = data;
  head_ = HEAD_AT_GPU;
  own_gpu_data_ = false;
#else
  NO_GPU;
#endif
}

if before call set_cpu_data(set_gpu_data), the head_ = SYNCED which means both gpu memory and cpu memory has mallced, so after call set_cpu_data(set_gpu_data), from the definition we could see the original mallced cpu(gpu) memory is set free, and assign a new data point, but the original gpu(cpu) memory has not be free, is this will cause memory leak?

in addition, l set_cpu_data(set_gpu_data) just transmit the pointer, we don't know the new memory block size, is this a problem?

[zhewang95]

I think set_cpu_data just means set the host(cpu side) memory, It has no need to deal with the device(gpu side) memory. The device memory will not be wasted because to_gpu(defined in syncedmem.cpp) can memcopy the data from cpu_ptr_ to gpu_ptr_.

[Noiredd]

There will be no memory leak - SyncedMemory frees its pointers upon its own destruction. When you feed it a new pointer (to memory you allocated manually), it takes ownership of it - it makes no difference whether the memory has been allocated by the object itself or by you. But when you replace a pointer with your own (set_&pu_data), it has to free the existing memory to avoid the leak.