could someone be so nice and explain me how to solve this problem?

in log nginx print:

2015/06/24 11:12:19 [alert] 2151#0: mmap(MAP_ANON|MAP_SHARED, 33554432) failed (12: Cannot allocate memory)

nginx.conf

user developer;
worker_processes auto;
pid /run/nginx.pid;

events {
    use epoll;
    worker_connections 30;
    multi_accept on;
}

http {

    ##
    # Basic Settings
    ##

    sendfile on;
    tcp_nopush on;
    tcp_nodelay on;
    #keepalive_timeout 65;
    keepalive_timeout 2;
    types_hash_max_size 2048;
    server_tokens off;

    # server_names_hash_bucket_size 64;
    # server_name_in_redirect off;

    include /etc/nginx/mime.types;
    default_type application/octet-stream;

    ##
    # Logging Settings
    ##

    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;

    ##
    # Gzip Settings
    ##

    gzip on;
    gzip_disable "msie6";
    gzip_min_length  1000;
    gzip_buffers     16 8k;

    gzip_types text/plain text/css application/json application/x-javascript text/xml application/xml application/xml+rss text/javascript;



    # MY CHANGES
    ssl_session_cache   shared:SSL:1m;
    ssl_session_timeout 5m;
    ssl_prefer_server_ciphers on;
    ssl_stapling on;
    resolver 8.8.8.8;
    geoip_country  /srv/www/geoipdb/GeoIP.dat;
    geoip_city     /srv/www/geoipdb/GeoLiteCity.dat;

    # Support the X-Forwarded-Proto header for fastcgi.
    map $http_x_forwarded_proto $fastcgi_https {
            default $https;
            http '';
            https on;
    }

    variables_hash_max_size 1024; # default 512
    upload_progress uploads 1m;

    include /etc/nginx/conf.d/*.conf;
    include apps/drupal/map_cache.conf;
    include /etc/nginx/sites-enabled/*;

}

cat /etc/sysctl.conf

kernel.shmmax = 68719476736
kernel.shmall = 4294967296

I have vps with 4G RAM.
in plesk memmory tab i see:

http://itmages.ru/image/view/2669317/4ab8f2d4

Thx in advance!