Here's an attempt at the script. Let's golf it!

  N=10
  find /sys/fs/cgroup/ -name memory.current | while read f; do
    test -e $f || continue
    echo `cat $f` $f
  done | sort -n | tail -n $N | awk '
  match($2, /system.slice.([a-z-]*).service/, arr) {
    $2 = "/system/" arr[1];
  }
  match($2, /user.slice.user-([0-9]*).slice/, arr) {
    cmd = "id -un " arr[1];
    cmd | getline uid;
    close(cmd);
    $2 = "/u/" uid;
  }
  match($2, /cgroup.([a-z]*).slice/, arr) {
    $2 = "/system/" arr[1];
  }
  { print }'