At first thanks for trying to help.
It's my fault that I messed up "top" to this story, just wanted to show that while my system is working just fine: 1. "used" and "real_used" fields of a process (tcp receiver) is bigger that I set in -M 2. "free" hasn't changed from the last restart.
root@proxy:~# kamcmd pkg.stats | grep '2480' -A 4 pid: 2480 rank: 17 used: 34156336 free: 32611216 real_used: 35228672
root@proxy:~# ps aux|grep 2480 kamailio 2480 0.0 0.3 348160 15836 ? S Sep23 0:10 /usr/local/kamailio-master/sbin/kamailio -f /etc/kamailio/kamailio.cfg -P /var/run/kamailio/kamailio.pid -m 128 -M 32 -u kamailio -g kamailio
root@proxy:~# kamctl ps | grep 2480 Process:: ID=22 PID=2480 Type=tcp receiver (generic) child=6