死亡Error：OSError: [Errno 12] Cannot allocate memory

    main()
  File "main.py", line 378, in main
    manager.prune()
  File "main.py", line 263, in prune
    savename='_final', best_accuracy=accuracy)
  File "main.py", line 217, in train
    self.do_epoch(epoch_idx, optimizer)
  File "main.py", line 174, in do_epoch
    for batch, label in tqdm(self.train_data_loader, desc='Epoch: %d ' % (epoch_idx)):
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/site-packages/tqdm/_tqdm.py", line 1032, in __iter__
    for obj in iterable:
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/site-packages/torch/utils/data/dataloader.py", line 301, in __iter__
    return DataLoaderIter(self)
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/site-packages/torch/utils/data/dataloader.py", line 158, in __init__
    w.start()
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/multiprocessing/process.py", line 105, in start
    self._popen = self._Popen(self)
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/multiprocessing/context.py", line 212, in _Popen
    return _default_context.get_context().Process._Popen(process_obj)
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/multiprocessing/context.py", line 267, in _Popen
    return Popen(process_obj)
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/multiprocessing/popen_fork.py", line 20, in __init__
    self._launch(process_obj)
  File "/home/rvlg/anaconda3/envs/torch/lib/python3.5/multiprocessing/popen_fork.py", line 67, in _launch
    self.pid = os.fork()
OSError: [Errno 12] Cannot allocate memory

遇到这个问题，由于代码本身的额原因先是考虑到运行电脑的内存问题，于是用

watch -n 2 nvidia-smi
watch -n 2 free -m

全程监视电脑CPU、GPU,以及物理内存、交换区内存的变化情况，发现并不是内存的原因。找bug未果。
换了一个思路，从出错的代码以及错误提示上来看，是dataloader.py出了问题，于是Google，关键词：dataloader OSError: [Errno 12] Cannot allocate memory
果然有很多人也是由于在dataload的时候出错，找了很多原因：
1、电脑内存原因（已排除）
2、电脑系统线程数量限制：https://blog.csdn.net/m0_37644085/article/details/92795488：修改最大进程数（尝试无效）
3、设置pin_memory=False；（尝试无效）
4、修改多线程数量：设置num_workers，系统默认的数量是4，改成1之后，没有效果，后面改成0，问题解决！！！程序可以跑了。
特发此帖纪念，认真查了两天多！！！希望可以帮到大家。