Create a CSV of each cgroup's memory.usage_in_bytes and some related memory.stat values.

collect_usage_in_bytes.sh

#!/bin/bash

printf '%s,%s,%s,%s,%s,%s,%s,%s\n' \
  'dir' 'usage_in_bytes' \
  'cache' 'total_cache' \
  'rss' 'total_rss' \
  'rss_huge' 'total_rss_huge'

cd /sys/fs/cgroup/memory/

while read -r usage_file
do
  dir=$(dirname "${usage_file}")
  usage_in_bytes=$(cat "${usage_file}")

  unset data
  declare -A data
  while read -r field value
  do
    data["${field}"]="${value}"
  done < <(grep 'cache\|rss' "${dir}/memory.stat")

  printf '%s,%s,%s,%s,%s,%s,%s,%s\n' \
    "${dir}" "${usage_in_bytes}" \
    "${data[cache]}" "${data[total_cache]}" \
    "${data[rss]}" "${data[total_rss]}" \
    "${data[rss_huge]}" "${data[total_rss_huge]}"

done < <(find . -name memory.usage_in_bytes)