Memory Management ( > 25GB memory usage)

Hello nginx!

I have one worker-process, which uses over 25GB memory (and doesn't stop to do that).
My configuration is... let's say special:

So there is nginx, which proxies all requests to the PHP backend and the PHP backend sends a large request back to nginx. I set the fastcgi_buffers very enormous huge to avoid nginx creating temporary files on my disk - which would result in high CPU load.

Here is my configuration: (reduced to the problem)

worker_processes 1;
worker_rlimit_nofile 80000;
worker_priority -20;

events {
worker_connections 10240;
multi_accept on;
}
# ...
# fastcgi settings
fastcgi_buffers 20480 1k;
fastcgi_connect_timeout 30;
fastcgi_read_timeout 30;
fastcgi_send_timeout 30;
fastcgi_keep_conn on;
upstream php-backend {
server 127.0.0.1:9000;
keepalive 10000;
}


As you can see the buffers are extreme large, to avoid disk buffering. The problem is that nginx doesn't free the buffers. It just eats and eats. I know it's my fault and not nginx' fault. What am I doing wrong?

The response of my php backend could be from 1k to 300mb.

What is the best setting for my situation?

Thanks