[ale] Allocation of memory

[Alex Carver]

Ok, I think I'm a bit fogged due to vacation (sure, that's the ticket)
so help me clear something up as I fiddle with a little coding project.

After reading and rereading and rerereading, the Linux Way (TM) of most
memory allocation for things like pthreads and the like is to ask for a
bunch of space and the OS will pseudo-grant that request with the caveat
that anything that isn't really and truly used can get swiped away for
something else.

By example, a little program I'm writing spawns a thread with each new
network connection using pthread_create.  I'm watching the processes
with top while testing (I'm trying to keep the program small and lean
but still handle multiple operations).  When it first starts up and no
threads have been spawned, I see a resident size and a data (stack) size
of some amount of kB.  When a thread is spawned, the resident size
increases slightly but the data-stack size jumps by about 8 MB per
thread (the default request for pthreads on Linux).  What I'm reading
says that the 8 MB isn't really 8 MB, it's just a request and probably
doesn't use all that much so the rest of the requested RAM that is
unused while the entire program is running could potentially go off to
another application.  Have I read that right?  When the threads close
down and all that's left is the main process, the data-stack amount
doesn't drop back down, it just sits there.

I'm asking because I'm trying to make sure this program has a small
memory footprint to start (which for the most part it does, resident
size is under 600 kB and the initial data-stack size is only 300 kB) but
I'll eventually run this program on a small machine so I don't want 8 MB
to just vanish every time a thread starts up.  It won't be many threads,
maybe 10 at the most but still, I want to try to use the least memory
possible just for fun.  :)