nginx log_format指令不起作用？

user  www;
worker_processes  1;

#error_log  logs/error.log;
#error_log  logs/error.log  notice;
#error_log  logs/error.log  info;

#pid        logs/nginx.pid;


events {
    worker_connections  1024;
}


http {
    include       mime.types;
    default_type  application/octet-stream;

    log_format  myformat  ' "$request" '
                      '  "$uri" '
                      '  "$args" '
                      '  ';

    #access_log  logs/access.log  main;

    sendfile        on;
    #tcp_nopush     on;

    #keepalive_timeout  0;
    keepalive_timeout  65;

    #gzip  on;



    server {
        listen       80;
        server_name  www.codebaa.com;
        charset utf-8;
        root /srv/www/codebaa/public;
        access_log  logs/www.codebaa.com.access.log myformat; 
        try_files $uri @rewrite;
        location ~ \.php.*$ {
            fastcgi_pass   unix:/var/run/php-fpm/php-fastcgi.socket;
            fastcgi_split_path_info       ^(.+\.php)(.*)$;
            include        fastcgi.conf;
        }

        location  @rewrite {
            rewrite ^(.*)$ /index.php?_url=$1;
        } 
        location ~ ^/ajax.*$ {
            rewrite ^/ajax/?(.*)$ /ajax.php?_url=/$1;    
        }
        location ~ ^/(img|js|css) {
            root /srv/www/codebaa/public;
        }  



    }

}

记录的日志是默认的格式：

192.168.153.1 - - [21/May/2015:15:57:41 +0800] "GET /questions HTTP/1.1" 200 14209 "-" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.152 Safari/537.36"

192.168.153.1 - - [21/May/2015:15:57:41 +0800] "GET /css/base.css HTTP/1.1" 200 9605 "http://www.codebaa.com/questions" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.152 Safari/537.36"
192.168.153.1 - - [21/May/2015:15:57:41 +0800] "GET /img/codebaa.png HTTP/1.1" 200 1389 "http://www.codebaa.com/questions" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.152 Safari/537.36"

192.168.153.1 - - [21/May/2015:15:57:41 +0800] "GET /js/jquery-1.11.2.min.js HTTP/1.1" 200 95931 "http://www.codebaa.com/questions" "Mozilla/5.0 (Windows NT 6.1) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/42.0.2311.152 Safari/537.36"
不知道哪里的问题，怎么搞都没用，版本是1.8.0的。