[PATCH RFC 2/9] bpftool: show memcg info of bpf map

[Yafang Shao <laoar.shao@xxxxxxxxx>]

bpf map can be charged to a memcg, so we'd better show the memcg info to
do better bpf memory management. This patch adds a new field
"memcg_state" to show whether a bpf map is charged to a memcg and
whether the memcg is offlined. Currently it has three values,
   0 : not charged
  -1 : the charged memcg is offline
   1 : the charged memcg is online

For instance,

$ bpftool map show
2: array  name iterator.rodata  flags 0x480
        key 4B  value 98B  max_entries 1  memlock 4096B
        btf_id 240  frozen
        memcg_state 0
3: hash  name calico_failsafe  flags 0x1
        key 4B  value 1B  max_entries 65535  memlock 524288B
        memcg_state 1
6: lru_hash  name access_record  flags 0x0
        key 8B  value 24B  max_entries 102400  memlock 3276800B
        btf_id 256
        memcg_state -1

Signed-off-by: Yafang Shao <laoar.shao@xxxxxxxxx>
---
 include/uapi/linux/bpf.h       |  1 +
 kernel/bpf/syscall.c           | 11 +++++++++++
 tools/bpf/bpftool/map.c        |  2 ++
 tools/include/uapi/linux/bpf.h |  1 +
 4 files changed, 15 insertions(+)

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 4eebea8..a448b06 100644
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -5864,6 +5864,7 @@ struct bpf_map_info {
 	__u32 btf_value_type_id;
 	__u32 :32;	/* alignment pad */
 	__u64 map_extra;
+	__s8  memcg_state;
 } __attribute__((aligned(8)));
 
 struct bpf_btf_info {
diff --git a/kernel/bpf/syscall.c b/kernel/bpf/syscall.c
index db402eb..3b50fcb 100644
--- a/kernel/bpf/syscall.c
+++ b/kernel/bpf/syscall.c
@@ -3939,6 +3939,17 @@ static int bpf_map_get_info_by_fd(struct file *file,
 	}
 	info.btf_vmlinux_value_type_id = map->btf_vmlinux_value_type_id;
 
+#ifdef CONFIG_MEMCG_KMEM
+	if (map->memcg) {
+		struct mem_cgroup *memcg = map->memcg;
+
+		if (memcg == root_mem_cgroup)
+			info.memcg_state = 0;
+		else
+			info.memcg_state = memcg->kmemcg_id < 0 ? -1 : 1;
+	}
+#endif
+
 	if (bpf_map_is_dev_bound(map)) {
 		err = bpf_map_offload_info_fill(&info, map);
 		if (err)
diff --git a/tools/bpf/bpftool/map.c b/tools/bpf/bpftool/map.c
index 0bba337..fe8322f 100644
--- a/tools/bpf/bpftool/map.c
+++ b/tools/bpf/bpftool/map.c
@@ -550,6 +550,7 @@ static int show_map_close_json(int fd, struct bpf_map_info *info)
 		jsonw_end_array(json_wtr);
 	}
 
+	jsonw_int_field(json_wtr, "memcg_state", info->memcg_state);
 	emit_obj_refs_json(refs_table, info->id, json_wtr);
 
 	jsonw_end_object(json_wtr);
@@ -635,6 +636,7 @@ static int show_map_close_plain(int fd, struct bpf_map_info *info)
 	if (frozen)
 		printf("%sfrozen", info->btf_id ? "  " : "");
 
+	printf("\n\tmemcg_state %d", info->memcg_state);
 	emit_obj_refs_plain(refs_table, info->id, "\n\tpids ");
 
 	printf("\n");
diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 4eebea8..41e65b3 100644
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -5864,6 +5864,7 @@ struct bpf_map_info {
 	__u32 btf_value_type_id;
 	__u32 :32;	/* alignment pad */
 	__u64 map_extra;
+	__s8 memcg_state;
 } __attribute__((aligned(8)));
 
 struct bpf_btf_info {
-- 
1.8.3.1