title: Celery raise MemoryError
body: <p>I'm using celery 4.3.0,And use it to generate a image which maybe 10M+,Then I got an error like below:</p>
  
  <pre><code>Pool callback raised exception: MemoryError('Process got: ')
  Traceback (most recent call last):
    File "*/lib/python3.7/site-packages/billiard/pool.py", line 1750, in safe_apply_callback
      fun(*args, **kwargs)
    File "*/lib/python3.7/site-packages/celery/worker/request.py", line 564, in on_success
      return self.on_failure(retval, return_ok=True)
    File "*/lib/python3.7/site-packages/celery/worker/request.py", line 351, in on_failure
      raise MemoryError('Process got: %s' % (exc_info.exception,))
  </code></pre>
  
  <p>My server has 20G+ memory left when running this task.And I had test some small images which work well.Do I need set some config to prevent this?</p>