Yes, thanks I got that.
Also I found another command :erlang.memory(:ets) which gives the data in bytes.

Looking to their docs it seems you can only control its size limit in number of entries, but @OvermindDL1 is a big fan of CacheX, thus he may tell you if is possible or not

I am able to get the table info by
IO.inspect(:ets.info(:my_cache_key))
as

[
  id: #Reference<0.1101184093.3508666371.167614>,
  read_concurrency: true,
  write_concurrency: true,
  compressed: false,
  memory: 40378, # Is this byte or KB?
  owner: #PID<0.589.0>,
  heir: #PID<0.588.0>,
  name: :my_cache_key,
  size: 2,
  node: :nonode@nohost,
  named_table: true,
  type: :set,
  keypos: 2,
  protection: :public
]

Now I am confuse about the unit of the memory.