apache, phusion passenger, and memory usage - ruby

Question

I read this article somewhere:
"With a plain Apache server, it doesn’t matter much if you run many child processes—the processes are about 1 MB each (most of it shared), so they don’t eat a lot of RAM. The situation is different with mod_perl, where the processes can easily grow to 10 MB and more. For example, if you have MaxClients set to 50, the memory usage becomes 50 × 10 MB = 500 MB.Do you have 500 MB of RAM dedicated to the mod_perl server?"
I'm not using mod_perl on my server. I am using phusion passenger and ruby on rails with apache2. I am using prefork MPM and the MaxClients is set to the default 256. That means I can have 256 processes running concurrently at any given time. The article piqued my interest because I never have 256 apache2 processes running concurrently, usually I only have 80 apache2 processes running at any given time. But sometimes even just 80 bogs down my server to the point where the site just hangs when you try to load it.
When I run the following command, it sometimes shows 80 apache2 processes, for example:
ps aux | grep apache2
USER PID %CPU %MEM VSZ RSS TTY STAT START TIME COMMAND
root 1130 0.0 0.1 149080 10600 ? Ss 12:36 0:00 /usr/sbin/apache2 -k start
www-data 2051 0.0 0.3 163608 23592 ? S 16:46 0:00 /usr/sbin/apache2 -k start
www-data 2506 0.0 0.1 149376 7952 ? S 16:47 0:00 /usr/sbin/apache2 -k start
www-data 5149 0.0 0.1 149416 7980 ? S 16:49 0:00 /usr/sbin/apache2 -k start
www-data 5175 0.0 0.1 149368 7876 ? S 16:49 0:00 /usr/sbin/apache2 -k start
www-data 10212 0.0 0.1 149368 7848 ? S 16:53 0:00 /usr/sbin/apache2 -k start
www-data 19114 0.0 0.1 149368 7904 ? S 17:01 0:00 /usr/sbin/apache2 -k start
www-data 19138 0.0 0.1 150768 11856 ? S 17:01 0:00 /usr/sbin/apache2 -k start
www-data 20592 0.0 0.1 149428 8092 ? S 16:35 0:00 /usr/sbin/apache2 -k start
www-data 21336 0.0 0.1 149368 7808 ? S 17:03 0:00 /usr/sbin/apache2 -k start
www-data 21375 0.0 0.1 149432 7916 ? S 17:03 0:00 /usr/sbin/apache2 -k start
1000 26458 0.0 0.0 8112 896 pts/6 S+ 17:07 0:00 grep apache2
www-data 30848 0.0 0.1 149396 8044 ? S 16:43 0:00 /usr/sbin/apache2 -k start
But under memory, they range from 0.1 to 0.4, which doesn't seem like a lot of memory. So my question is when you send a request to the site from the browser, in addition to spawning a new apache2 process as a child process to the parent apache2 process, does passenger also create another process, something that could possibly be bogging down memory? When I run the top command, I notice sometimes it shows a ruby process at %100 CPU. I am wondering is that ruby process somehow linked to the apache2 processes via passenger. Something must be causing these processes to grow to big memory consumers, like that article stated. There must be something I am not looking at.
By the way, I have more than 5 gigs of memory on the machine:
$ cat meminfo
MemTotal: 6113156 kB

Answer 1

Phusion Passenger spawns your Ruby application processes separately. View them with passenger-memory-stats or passenger-status.