Description of problem:
两个问题：
1.4.19 x86 上脏内存回收后，memory.dirty_throttle_latency中没有记录,全为0
2.4.19 arm以及5.10 x86/arm上，不存在/sys/fs/cgroup/memory/memory.dirty_throttle_latency文件，请确认是否需要支持

Version-Release number of selected component (if applicable):
# uname -a
Linux i22e11410.eu95sqa 4.19.91-231.git.533d40934.an8.x86_64 #1 SMP Mon Feb 14 13:30:06 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
[root@i22e11410 bin]# cat /etc/os-release
NAME="Anolis OS"
VERSION="8.2"
ID="anolis"
ID_LIKE="rhel fedora centos"
VERSION_ID="8.2"
PLATFORM_ID="platform:an8"
PRETTY_NAME="Anolis OS 8.2"
ANSI_COLOR="0;31"
HOME_URL="https://openanolis.cn/"

How reproducible:
# show dirty throttle latency for memcg in memory.dirty_throttle_latency.
# Test process:
# 1)trigger memory dirty throttle in memcg;
# in memcg, run process to write memory bigger than parent-memcg's
# memory.limit_in_bytes to disk.
# 2)check if sum of child's dirty throttle lat for memcg is less than
# or equal to their parent.


Steps to Reproduce:
1.setup
memcg_mnt=`grep -w memory /proc/mounts | cut -f 2 | cut -d " " -f2`
[ ! -d "$memcg_mnt" ] && mkdir -p $memcg_mnt && mount -t cgroup -o memory cgroup $memcg_mnt

head -c 20000M /dev/zero > ~/10g
testpath=$memcg_mnt/foo
mkdir -p $testpath/sub

# parent memcg's mem limit: 5M
memlimit_p=5242880

# child memcg's mem limit: 20M
memlimit_c=20971520
echo $memlimit_p > "$testpath/memory.limit_in_bytes"
echo $memlimit_c > "$testpath/sub/memory.limit_in_bytes"
sync
echo 3 > "/proc/sys/vm/drop_caches"

path_c=$testpath/sub/memory.dirty_throttle_latency
path_p=$testpath/memory.dirty_throttle_latency

# clear all lat info
echo 0 > ${path_c}
echo 0 > ${path_p}


2.# in memcg, run process to write 1000MB memory to disk,
  # which is bigger than parent-memcg's memory.limit_in_bytes(50MB).
  # that would cause dirty throttle in curent memcg.

echo $$ > $testpath/sub/tasks

head -c 2000M ~/10g > /dev/null
head -c 1000M /dev/zero > ~/10g
sleep 1
echo $$ > $memcg_mnt/tasks

3. # check if sum of child's dirty throttle lat for memcgis less than or equal to their parent
# and the value can not be all zero
cat $path_c
cat $path_p


Actual results:
1.4.19 x86 上脏内存回收后，memory.dirty_throttle_latency中没有记录,全为0
2.4.19 arm以及5.10 x86/arm上，不存在/sys/fs/cgroup/memory/memory.dirty_throttle_latency文件，请确认是否需要支持

cat /sys/fs/cgroup/memory/foo/sub/memory.dirty_throttle_latency
0-1ms:  0
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      0
cat /sys/fs/cgroup/memory/foo/memory.dirty_throttle_latency
0-1ms:  0
1-5ms:  0
5-10ms:         0
10-100ms:       0
100-500ms:      0
500-1000ms:     0
>=1000ms:       0
total(ms):      0

Expected results:
1.sum of child's dirty throttle lat for memcg is less than or equal to their parent
2.the value can not be all zero

Additional info: