Memory overhead when using lua-nginx-module

I have nginx with lua-nginx-module.
When I send range requests to nginx with lua-nginx-module and enabled http_slice_module, nginx takes all free memory and does not free even if all connections closed.
Without lua-nginx-module nginx does not use so much memory, one of worker processes can use some memory and free it during work.

$ nginx -V
nginx version: nginx/1.11.2
built by gcc 4.8.4 (Ubuntu 4.8.4-2ubuntu1~14.04.3)
built with OpenSSL 1.0.1f 6 Jan 2014
TLS SNI support enabled
configure arguments: --prefix=/etc/nginx --sbin-path=/usr/sbin/nginx --modules-path=/usr/lib/nginx/modules --conf-path=/etc/nginx/nginx.conf --error-log-path=/var/log/nginx/error.log --http-log-path=/var/log/nginx/access.log --pid-path=/var/run/nginx.pid --lock-path=/var/run/nginx.lock --http-client-body-temp-path=/var/cache/nginx/client_temp --http-proxy-temp-path=/var/cache/nginx/proxy_temp --http-fastcgi-temp-path=/var/cache/nginx/fastcgi_temp --http-uwsgi-temp-path=/var/cache/nginx/uwsgi_temp --http-scgi-temp-path=/var/cache/nginx/scgi_temp --user=nginx --group=nginx --with-http_ssl_module --with-http_realip_module --with-http_addition_module --with-http_sub_module --with-http_dav_module --with-http_flv_module --with-http_mp4_module --with-http_gunzip_module --with-http_gzip_static_module --with-http_random_index_module --with-http_secure_link_module --with-http_stub_status_module --with-http_auth_request_module --with-http_xslt_module=dynamic --with-http_image_filter_module=dynamic --with-http_geoip_module=dynamic --with-http_perl_module=dynamic --add-dynamic-module=debian/extra/njs-ef2b708510b1/nginx --with-threads --with-stream --with-stream_ssl_module --with-http_slice_module --with-mail --with-mail_ssl_module --with-file-aio --with-ipv6 --with-http_v2_module --with-cc-opt='-g -O2 -fstack-protector --param=ssp-buffer-size=4 -Wformat -Werror=format-security' --with-ld-opt='-Wl,-Bsymbolic-functions -Wl,-z,relro' --add-module=ngx_devel_kit-0.3.0 --add-module=lua-nginx-module-0.10.6

libluajit-5.1-2 version:

$ ldd /usr/sbin/nginx | grep lua
    libluajit-5.1.so.2 => /usr/lib/x86_64-linux-gnu/libluajit-5.1.so.2 
$ ls -al /usr/lib/x86_64-linux-gnu/libluajit-5.1.so.2
lrwxrwxrwx 1 root root 22 Jun  9  2013 /usr/lib/x86_64-linux-gnu/libluajit-5.1.so.2 -> libluajit-5.1.so.2.0.2

With libluajit-5.1.so.2.0.4 memory usage same as with libluajit-5.1.so.2.0.2.

For example nginx with lua-nginx-module:

memory usage before test:

$ ps -e -orss=,args= | grep nginx: | awk 'BEGIN{sum=0;}{sum+=$1; print $0; }END{print "Total memory = ", sum;}'
 2712 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
13340 nginx: worker process
 3360 nginx: cache manager process
 2948 nginx: cache loader process
  944 grep --color=auto nginx:
Total memory =  223404

memory usage after test (all requests finished and all connections to nginx closed):

$ ps -e -orss=,args= | grep nginx: | awk 'BEGIN{sum=0;}{sum+=$1; print $0; }END{print "Total memory = ", sum;}'
 2372 nginx: master process /usr/sbin/nginx -c /etc/nginx/nginx.conf
2033368 nginx: worker process
1993736 nginx: worker process
2010688 nginx: worker process
2072408 nginx: worker process
1899844 nginx: worker process
2036096 nginx: worker process
2081336 nginx: worker process
1829648 nginx: worker process
1992792 nginx: worker process
1705992 nginx: worker process
2074204 nginx: worker process
1805180 nginx: worker process
2003932 nginx: worker process
1902636 nginx: worker process
2081448 nginx: worker process
2048644 nginx: worker process
 3008 nginx: cache manager process
  804 grep --color=auto nginx:
Total memory =  31578136

nginx config:

worker_processes  16;
worker_rlimit_nofile 1000000;

events {
}

http {
    output_buffers            1 1m;

    log_format main '$remote_addr [$time_local] "$request" $status $bytes_sent'
                    ' "$request_time" "$upstream_cache_status" "$http_range"';

    proxy_cache_path       /var/cache/nginx/proxy_cache levels=2:2 keys_zone=proxy_slice:500m inactive=3d use_temp_path=off;

    server {
      listen      127.0.0.1:8080 default_server backlog=65535;
      access_log  /var/log/nginx/proxy_slice.log main;

      slice             1m;
      proxy_cache       proxy_slice;
      proxy_cache_key   "$request_uri|$slice_range";
      proxy_cache_valid 200 206 1d;
      proxy_cache_valid any 0;
      proxy_set_header  Range    $slice_range;
      proxy_ignore_client_abort on;
      proxy_http_version 1.1;

      location / {
        proxy_pass http://127.0.0.1:8088;
      }
    }

    server {
      listen 127.0.0.1:8088;

      access_log /var/log/nginx/storage.log main;
      rewrite ^.*$ /1.data last;

      location / {
        root /var/data;
      }
    }
}

How to reproduce:

$ mkdir /var/data; 
$ dd if=/dev/urandom of=/var/data/1.data bs=1M count=4500

Command for test:

$ while true; do curl -H "Range: bytes=$(echo $(od -An -N3 -i /dev/urandom)-$(( 100 * $(od -An -N3 -i /dev/urandom) )))" "http://127.0.0.1:8080/$(head /dev/urandom | tr -dc A-Za-z0-9 | head -c 13)" > /dev/null ; done

Reproduce the reported RSS growth with the supplied nginx configuration, http_slice_module, lua-nginx-module, and range-request loop, then compare behavior with lua-nginx-module disabled. Trace the interaction between the two modules and verify memory after connections close; done means identifying the retention cause and demonstrating that the corrected behavior persists under the reproduction.