hulk inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I4MC3F
CVE: NA

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Multiple operations on cgroups in cgroup v1 are related to the status
of the cgroup. The status of the current cgroup can be displayed in
cgroupv2, but it cannot be displayed in cgroup v1, so the
cgroup.flag_stat member is added in memory cgroup to display the
status of the current cgroup and sub-cgroups.

Testing result:
List the status of user.slice
[root@test user.slice]#cat memory.flag_stat
NO_REF 0
ONLINE 1
RELEASED 0
VISIBLE 1
DYING 0
CHILD_NO_REF 0
CHILD_ONLINE 1
CHILD_RELEASED 0
CHILD_VISIBLE 1
CHILD_DYING 0

Create a new cgroup in user.slice
[root@test user.slice]#mkdir user-test

List the current status of user.slice after operation above
[root@test user.slice]#cat memory.flag_stat
NO_REF 0
ONLINE 1
RELEASED 0
VISIBLE 1
DYING 0
CHILD_NO_REF 0
CHILD_ONLINE 2
CHILD_RELEASED 0
CHILD_VISIBLE 2
CHILD_DYING 0
Signed-off-by: Ntatataeki <shengzeyu19_98@163.com>
Reviewed-by: NKefeng Wang <wangkefeng.wang@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>