RuntimeError: CUDA out of memory. Tried to allocate 2.14 GiB (GPU 0; 6.00 GiB total capacity; 717.82 MiB already allocated; 3.31 GiB free; 780.00 MiB reserved in total by PyTorch)GPU空闲内存比需要的内存大很多，但是却出现了CUDA内存不足，这种问题该怎么办？？