我从一篇文档上截取下来的几块描述：

1.Further bolstering its reputation as a good open source citizens,Facebook has open sourced an in-house developed tool called watchman,designed to help Web developers speed up build times by automatically tracking file changes and kicking off automated responses.

2.Facebook's engineering team used Watchman,which runs on Linux,OS X,FreeBSD,and Solaris,to kick off builds while engineers are editing files. "Between this and more intelligent incremental processing,we've been able to reduce our interactive-user p50 build times by 60 percent," Furlong wrote. "It's not a silver bullet for making builds go fast,but it has helped us to make noticeable improvements both here and in some other internal projects."

总结一下：watchman是个文件监控系统，他优化的是reload文件遍历机制，加入watchman的RN，reload会加快，没加的会遍历量很高，很慢

文章地址：http://www.tuicool.com/articles/Z3UFzu