Which is curious. Some content you run into by accident and think needs reposting. But how does one stumble upon this post in 2015? Googling for "why is gnu grep fast" and then not noticing that two of the top four results are submissions to HN?
Finding it linked from some other article or blog post, or having it sent to you from someone else and then assuming that a mail thread from 2010 has never been seen on HN before.