ASUS RT-AX82U (v1) (3004.388.9_2-gnuton2) low memory - how to create swap?

[Litburg24]

Hi.
ASUS RT-AX82U (v1) / firmware 3004.388.9_2-gnuton2

Low memory:

_free -h_

total          used          free           shared    buffers     cached
Mem:        512188     460684      51504      45480      14560     122788
-/+ buffers/cache:     323336     188852
Swap:            0          0          0

Everything works manually:

#!/bin/sh
SWAPFILE="/tmp/mnt/DISK_IMG/swapfile"
if [ -f "$SWAPFILE" ]; then
    swapon "$SWAPFILE"
fi

But nothing starts automatically (at boot):
/opt/etc/init.d/S99swap - not work
/jffs/S99swap - not work
/jffs/services-start - not work = renamed "S99swap"
/jffs/init-start - not work = "mv /jffs/services-start"
/etc/openvpn/server1/vpn-watchdog1.sh - after reboot always restores original content
/jffs/init-start - not work
/jffs/post-mount - not work

Everything works manually. After reboot nothing works.
Tell me - where should I look for a solution?