bpf: arraymap memory usage

bpf: arraymap memory usage

Introduce array_map_mem_usage() to calculate arraymap memory usage. In
this helper, some small memory allocations are ignored, like the
allocation of struct bpf_array_aux in prog_array. The inner_map_meta in
array_of_map is also ignored.

The result as follows,

- before
11: array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B
12: percpu_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 8912896B
13: perf_event_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B
14: prog_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B
15: cgroup_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524288B

- after
11: array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524608B
12: percpu_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 17301824B
13: perf_event_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524608B
14: prog_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524608B
15: cgroup_array  name count_map  flags 0x0
        key 4B  value 4B  max_entries 65536  memlock 524608B

Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-5-laoar.shao@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>