From: Yohanes Santoso <ysantoso-rubytalk@...>
Date: 2004-08-27T02:28:10+09:00
Subject: Re: Ruby interpreter as client-server

MiG <mig@1984.cz> writes:

> Have you any idea how to get the real memory usage of each process?

There is no easy way to get accurate real memory usage of each
process, especially those that are just freshly forked.

BTW, the 'real' memory usage is the RSS column, not VSZ. VSZ is the
size in virtual memory. VSZ-RSS is the size on swap or will be swapped
without further examination.

Take for example:

dede:~$ ps -ao pid,vsz,rss,command|grep ruby
 3086  3012 1364 ruby1.8 -e fork { sleep(9999) }; Process.wait
 3087  3016 1376 ruby1.8 -e fork { sleep(9999) }; Process.wait

The above does not necessarily mean that these two processes combined
use 1364+1376=2740 KB. Most UNIX-like OSes perform copy-on-write
(CoW). Meaning, if you fork but do not modify anything, then you will
only incur the cost to track another process in the kernel (around
12KB or so in Linux).

YS.