"buffers" RAM use under Linux while running nginx

[Leigh Dyer]

Hi all,

I have a couple of web servers running nginx 1.0.4 on Ubuntu 10.04 
AMD64, serving several hundred GB of static images. Each machine has 4GB 
of RAM, but less than 1GB is used by the Linux page cache, because 
there's more than 2GB assigned to "buffers". Here's the output from the 
"free" on one of them:

            total       used       free     shared    buffers     cached
Mem:     4057484    4024404      33080          0    2421352     947772
-/+ buffers/cache:   655280    3402204
Swap:    3998712          0    3998712

 From what I understand, "buffers" includes the TCP send buffers for 
each outgoing connection, and might include read buffers for each file 
that's in transit, but I'm surprised that it's adding up to 2.4GB.

Is this expected behaviour? Is there any way I can reduce those buffers 
to get more cache RAM, or should I just throw more RAM in these machines?

Thanks
Leigh