How can i limit docker container's RAM

my divece is raspberry 4b , i have tried a lot of ways but all failed.docker on openwrt(my os is openwrt) will warning limit memory is not supported, i want to enable grub but i always failed.Then i want to use CGroup to limit the container,but i noticed that my /sys/fs/cgroup dont have file named memory ,and i cannot use CGroup to limit my RAM with the tutorial in google. I am so confused ,can someone help me.
when i enter docker info ,it will show this


so, just to be clear, you are running OpenWrt as host (on the rpi itself) and not as docker container right?

yes openwrt is my OS on the rpi