[osandov]

> I don't get why BFQ hasn't been mainlined yet

BFQ hasn't been mainlined because it is written for the legacy block layer in the Linux kernel, which will be replaced entirely with the new block multiqueue implementation. It doesn't make much sense to replace CFQ or add a brand new scheduler only to rip it out in a few releases. Linux 4.11 will have support for I/O scheduling for blk-mq. BFQ is currently being ported to blk-mq; that work is the first big hurdle to getting it merged.