It is no secret that much of the work on the in-kernel BPF virtual machine
and associated user-space support code is being done at Facebook. But less
is known about how Facebook is actually using BPF. At Kernel Recipes 2019,
BPF developer Alexei Starovoitov described
a bit of that work, though even he admitted that he didn’t know what most
of the BPF programs running there were doing. He also summarized recent
developments with BPF and some near-future work.

Source: LWN.net – [$] BPF at Facebook (and beyond)