scrapy 如何知晓本次爬取所用流量？

{'downloader/request_bytes': 95469,
 'downloader/request_count': 334,
 'downloader/request_method_count/GET': 334,
 'downloader/response_bytes': 3415991,
 'downloader/response_count': 334,
 'downloader/response_status_count/200': 334,
 'finish_reason': 'reached limits :count=300',
 'finish_time': datetime.datetime(2015, 10, 28, 7, 17, 23, 855091),
 'item_scraped_count': 300,
 'log_count/DEBUG': 635,
 'log_count/INFO': 7,
 'request_depth_max': 18,
 'response_received_count': 334,
 'scheduler/dequeued': 334,
 'scheduler/dequeued/memory': 334,
 'scheduler/enqueued': 731,
 'scheduler/enqueued/memory': 731,
 'start_time': datetime.datetime(2015, 10, 28, 7, 16, 25, 680521)}

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downloader的stats已经给的很清楚了，把request bytes 和 response bytes加起来就行