How to set a limit for a specific client in nginx?

Question

Nginx

Hello! A webdav service is organized, via python wscgi, nginx is used as a proxy.
Faced a problem that when clients use Disk0 from mail.ru for connection, the server simply "lays down". A bunch of a bunch of processes are created, as I understand from the logs, the client simply scans the information. There is a lot of information, and such connections simply "lose" the service.
At the moment, I solved the problem radically, by:
if ($http_user_agent ~* CloudDiskO*) {
return 403;
}
But now, actually, a question. Is it possible, through the same if ($http_user_agent ~* CloudDiskO*) directive, to painlessly limit the possible number of connections?