Question about 'top' values on memory usage

[Artem Kuchin]

Hello!

Maybe someone with deeper knowledge of the internals of FreeBSD
can  clean up something for me (any for many others)^

Here are lines from my top:

  PID USERNAME    THR PRI NICE   SIZE    RES STATE  C   TIME   WCPU COMMAND
 9258 hordelo_ru    1   4    0 40992K  4260K accept 0   0:00  0.00% httpd
 9257 hordelo_ru    1  44    0 40992K  4296K select 1   0:00  0.00% httpd
 9259 hordelo_ru    1   4    0 40992K  4292K select 1   0:00  0.00% httpd

As you see, 'size' is the same for all processes, while RES varies.

As i understand, the real memory taken by a process is RES and SIZE include
a bunch of shares .so libs, so, if more httpd's started each will take
only about 4300K more, so, 100 https will take 430000K to run, right?

Another question is that is httpd uses threads (as provided by FreeBSD)
starting a new thread will or will not copy executable copy and data? Basically,
will a new thread eat another 4300K or just a little bit for its data?

All this i need to calculate maximum possible number of https i can run on a box
with certain amount of memory and select proper MPM for Apache.
Somehow, i could not find any practical info on this regarding FreeBSD.

Thank you in  advance!

--
Regards,
Artem Kuchin