I read it was only mainlined last year following this thread[1] where a kernel dev presented benchmarks and advised "zstd is an improvement on almost all metrics"

Of course zstd somewhat of a portfolio project of facebook developers, and they seem to have integrated it quite nicely into Btrfs to atone for their debt to society - I'll take that :D

[1] https://lore.kernel.org/lkml/1588791882.08g1378g67.none@loca...