> The thing I don't understand, is why work isn't
> done to make btrfs fit this use case. It already
> has less write amplification than ext4 or xfs
> due to it's COW nature (I think Arnd Bergmann
> did some research on that).
There is currently some work going into btrfs to make it a better match for SSDs. That would probably make an interesting LWN article of its own. Also keep in mind that the type of SSD you see on a desktop is much different than what you see in a mobile phone. The firmware is much fancier and so an optimization for one may be a pessimization for the other.