That's probably just normal apache growth-- possibly nothing to do
with modperl

i'd suggest using:
Devel::GC::Helper
and
Devel::Leak

to check refcounts... see what's going on

There's a lot of crazy ways you can have process growth within mod-
perl that are just perl issues:

a- there's a slight leak in string evals , its fixed in 5.9, but
5.8.8 has it
b- DBI keeps an internal cache of 120 statement handles and
connection handles. so you'll see it grow quite a bit, then reset
later on. if you use dbi (or apache::session mysql/postgres/etc ),
expect it to consume some internal memory for the cache.

there are more, those are just off the top of my head.

i'd suggest measuring the process size between 1 and 1000 requests.
often you'll see stuff taper off as perl caches more data or uses
larger variables. You can also use sizelimit to force a reset, or
use maxrequests to spawn a new child in a sweet-spot around 200-750
requests.