The BPF subsystem, which allows code to be loaded into the kernel from user
space and safely executed in the kernel context, is bound to create a number of
challenges for the kernel as a whole. One might not think that allocating
memory for BPF programs would be high on the list of problems, but life
(and memory management) can be surprising. The attempts to do a better job
of providing space for compiled BPF code have, to date, only been partially
successful; now Song Liu is back with a new
approach to finish the job.

Source: LWN.net – [$] Yet another try at the BPF program allocator