Nginx + Passenger turn on gzip not take effect - ruby-on-rails-3

Question

Try to turn on Nginx gzip feature to save some bandwidth, but no luck.
Searching for hours still can not make it work.
Nginx is installed by Passenger. Here is the information about Nginx in my server:
nginx version: nginx/1.4.1
built by gcc 4.6.3 (Ubuntu/Linaro 4.6.3-1ubuntu5)
TLS SNI support enabled
configure arguments: --prefix=/opt/nginx --with-http_ssl_module --with-http_gzip_static_module --with-http_stub_status_module --with-cc-opt=-Wno-error --add-module=/home/lijc/.rvm/gems/ruby-1.9.3-p392#rails3.2/gems/passenger-4.0.2/ext/nginx
Nginx.conf:
worker_processes 1;
events {
worker_connections 1024;
}
http {
passenger_root /home/lijc/.rvm/gems/ruby-1.9.3-p392#rails3.2/gems/passenger-4.0.2;
passenger_ruby /home/lijc/.rvm/wrappers/ruby-1.9.3-p392#rails3.2/ruby;
include mime.types;
default_type application/octet-stream;
sendfile on;
client_max_body_size 100m;
keepalive_timeout 65;
gzip on;
gzip_min_length 1k;
gzip_disable "MSIE [1-6]\.";
gzip_http_version 1.1;
gzip_types text/plain text/css application/x-javascript application/xml application/json application/atom+xml application/rss+xml;
gzip_vary on;
server {
listen 80;
server_name localhost;
root /home/lijc/web/rails/jasli2team/evolution/public;
passenger_enabled on;
}
}
Then restart Nginx and Passenger. However with Chrome dev tools. The header return by my site still not including Content-Encoding:gzip
Here is the header return by my site:
Cache-Control:must-revalidate, private, max-age=0
Content-Type:text/html; charset=utf-8
Date:Wed, 05 Jun 2013 02:55:47 GMT
ETag:"f5a1b272c96c5786342ec4bfd9b6e608"
Proxy-Connection:close
Server:nginx/1.4.1 + Phusion Passenger 4.0.2
Status:200 OK
Vary:Accept-Encoding
Via:1.0 localhost.localdomain:1080 (squid/2.6.STABLE16)
X-Cache:MISS from localhost.localdomain
X-Cache-Lookup:MISS from localhost.localdomain:1080
X-Powered-By:Phusion Passenger 4.0.2
X-Rack-Cache:miss
X-Request-Id:8353874387ca7510158dd5bf93b37ab9
X-Runtime:0.042863
X-UA-Compatible:IE=Edge,chrome=1
I have no idea what is wrong or missing. Any help will be appreciated.