[plug] free(1), buffers and squid

[Christian]

Hi all,

The answer to this should be pretty simple but I can't seem to find it
document properly anywhere.  Basically I'm tuning the cache_mem
parameter for squid and trying to maximise the efficiency of the usage
of available memory while keeping enough in reserve to handle load
spikes for the other things that the machine is doing (web, mail and
DNS).  While vmstat is occasionally useful for this, the main tool I'm
using is free(1).  Eg:

eagle:~# free
             total       used       free     shared    buffers    
cached
Mem:        582612     579148       3464      76968     180244    
311260
-/+ buffers/cache:      87644     494968
Swap:       522208        528     521680

My problem is the exact interpretation of the buffers/cached
information: what is the difference between the two?  Looking at the top
line it seems that I have only 3 megs of memory free, however, looking
at the line below it the figure seems to indicate that i have 494 megs
free (I assume this would be a maximum value with absolutely no
filesystem caching and really bad performance).  Can someone explain
exactly how these two parameters influence available memory and/or
provide any tips for tuning squid's memory usage?

Regards,

Christian.