unix memory question

[Thomas Cameron]

On Sun, 2005-06-12 at 10:32 -0700, jim martin wrote:
> Hi.. I am curious to know how unix define memory usage.  When I type "free" or top, I saw the used
> memory is so much as shown below.  But my server is actually idle.  In the top's process show that
> the highest memory usage process is only taking up 0.5%. why? the Free command shows used memory
> is so much?
> 
> [root at wat]# free
>      total  used    free   shared  buffers   cached
> Mem: 1027344 922496 104848   0     124304     589148
> 
> -/+ buffers/cache:     209044     818300
> Swap:      2031608          0    2031608


Your system appears to be mostly free.  Linux is very aggressive at
caching things in memory before writing them to disk and keeping
previously used information in memory in case it's needed again.  That's
part of why you see the "cached" section at almost 600MB.  Also, your
swap file isn't being touched - another indicator that your machine is
fine with memory.

Until you see low cached memory and lots of used swap space, your
machine is just fine.

> Besides, I heard from my friend that there is a method to allocate memory for different process.
> For example 30% for apache and 40% for tomcat. Is that true? How to do it?

Sorry, I am not sure.

Thomas