It seems that discoverer process is leaking memory. On a test system it looks like:
PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
31726 demo 25 5 246m 59m 1920 S 0 1.0 0:30.80 zabbix_server
RES & SHR numbers are growing.
I will attach screenshot with configuration of discovery rules shortly.