I converted the .dtb file to .tds and saw that the 2G ram information is correct. I did everything I can never use more than 720Mb of RAM, after that, use the zram. As the free command shows.

 

my box is S905x 2GB and kernel 5.1.0-aml-s905 #5.90 SMP PREEMPT Mon Jul 1 15:40:37 MSK 2019 aarch64 GNU/Linux

 

 

oot@fenix:/boot/dtb# free
              total        used        free      shared  buff/cache   available
Mem:        1849584      713516      883136       41232      252932     1019832
Swap:       2774372      381696     2392676

It appears that in 2GB of RAM but only uses 720Mb what to do?

 

 

I turned off the zram0 swap service and still does not use all the memory. what to do. I installed a new kernel not solved I tried some 10 different .dtb not solved!

 

http://ix.io/2jA5
 

the best regards

5.90 | arm64 | aarch64 | 5.1.0-aml-s905

Your Armbian seems way outdated. Try a up-to-date image on a different sd card or upgrade your kernel package at least.

I have a Le Potato sbc (s905x) and i have encountered the same bug. It has to do with the cma memory allocation used by the gpu that reserve memory, making it unavailable for the cpu. After reporting on this forum, some community members quickly found the problem and fix it. This bug should be already fixed with last kernels, you only need to update (now i have 5.4.28-meson64). Thanks again for the support!