如何使用c#中的迭代器反向读取文本文件

I need to process a large file, around 400K lines and 200 M. But sometimes I have to process from bottom up. How can I use iterator (yield return) here? Basically I don't like to load everything in memory. I know it is more efficient to use iterator in .NET.I need to process a large file, around 400K lin