docs/bpf: Add LRU internals description and graph

Extend the bpf hashmap docs to include a brief description of the
internals of the LRU map type (setting appropriate API expectations),
including the original commit message from Martin and a variant on the
graph that I had presented during my Linux Plumbers Conference 2022
talk on "Pressure feedback for LRU map types"[0].

The node names in the dot file correspond roughly to the functions
where the logic for those decisions or steps is defined, to help
curious developers to cross-reference and update this logic if the
details of the LRU implementation ever differ from this description.

  [0] https://lpc.events/event/16/contributions/1368/

Signed-off-by: Joe Stringer <[email protected]>
Signed-off-by: Daniel Borkmann <[email protected]>
Reviewed-by: Bagas Sanjaya <[email protected]>
Acked-by: John Fastabend <[email protected]>
Link: https://lore.kernel.org/bpf/[email protected]

0 files changed, 0 insertions, 0 deletions