bpf: queue_stack_maps memory usage

A new helper is introduced to calculate queue_stack_maps memory usage.

The result as follows,

- before
20: queue  name count_map  flags 0x0
        key 0B  value 4B  max_entries 65536  memlock 266240B
21: stack  name count_map  flags 0x0
        key 0B  value 4B  max_entries 65536  memlock 266240B

- after
20: queue  name count_map  flags 0x0
        key 0B  value 4B  max_entries 65536  memlock 524288B
21: stack  name count_map  flags 0x0
        key 0B  value 4B  max_entries 65536  memlock 524288B
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Link: https://lore.kernel.org/r/20230305124615.12358-12-laoar.shao@gmail.comSigned-off-by: Alexei Starovoitov <ast@kernel.org>

kernel/bpf/queue_stack_maps.c

@@ -246,6 +246,14 @@ static int queue_stack_map_get_next_key(struct bpf_map *map, void *key,
 	return -EINVAL;
 }
 
+static u64 queue_stack_map_mem_usage(const struct bpf_map *map)
+{
+	u64 usage = sizeof(struct bpf_queue_stack);
+
+	usage += ((u64)map->max_entries + 1) * map->value_size;
+	return usage;
+}
+
 BTF_ID_LIST_SINGLE(queue_map_btf_ids, struct, bpf_queue_stack)
 const struct bpf_map_ops queue_map_ops = {
 	.map_meta_equal = bpf_map_meta_equal,
@@ -259,6 +267,7 @@ const struct bpf_map_ops queue_map_ops = {
 	.map_pop_elem = queue_map_pop_elem,
 	.map_peek_elem = queue_map_peek_elem,
 	.map_get_next_key = queue_stack_map_get_next_key,
+	.map_mem_usage = queue_stack_map_mem_usage,
 	.map_btf_id = &queue_map_btf_ids[0],
 };
 
@@ -274,5 +283,6 @@ const struct bpf_map_ops stack_map_ops = {
 	.map_pop_elem = stack_map_pop_elem,
 	.map_peek_elem = stack_map_peek_elem,
 	.map_get_next_key = queue_stack_map_get_next_key,
+	.map_mem_usage = queue_stack_map_mem_usage,
 	.map_btf_id = &queue_map_btf_ids[0],
 };