Memory split - bananapi m1 +

I am trying to enable memory split on my board.  I am using  Armbian Stretch with mainline based kernel 4.19.y.

No matter what I do, after reboot I get:

root@bananapi:~# free -h
              total        used        free      shared  buff/cache   available
Mem:           996M        170M        613M        4.8M        212M        799M
Swap:          498M          0B        498M

I've already tried adding to armbianEnv.txt:

disp_mem_reserves=on
extraargs=cma=96M

After first boot I've already relinked /boot/script.bin to /boot/bin/bananapim1plus.bin and added fdtfile=sun7i-a20-bananapi-m1-plus.dtb to /boot/armbianEnv.txt in order to have wifi.

Additionally, when I tried to use Armbian Xenial with desktop legacy kernel 3.4.y, but it doesn't seem to be able to get wifi working, cause after I've added fdtfile=sun7i-a20-bananapi-m1-plus.dtb to /boot/armbianEnv.txt system stopped booting.

Does anyone know how to get memory split to work?

Thanks in advance