> I'm afraid to say that you'll have to post a short reproducer here
> before I can look at this further ...

I'm not sure this is the same issue. Look at this test code:

================================
let threads_counter = ref 0

let counter_mutex = Mutex.create ()

let send_data data size =
	let fd = Unix.openfile "/dev/null" [ Unix.O_WRONLY ] 0o644 in
	ignore (Unix.write fd data 0 size);
	Unix.close fd

let read_data _ =
	let fd = Unix.openfile "/dev/random" [] 0o644 in
	let buffer = String.create 1024 in
	let br = Unix.read fd buffer 0 (Random.int 1000) in
	Unix.close fd;
	ignore (Unix.select [] [] [] 0.1);
	send_data buffer br

let do_work _ =
	read_data ();

	Mutex.lock counter_mutex;
	decr threads_counter;
	Mutex.unlock counter_mutex

let _ =
	while true do
		Mutex.lock counter_mutex;
		if !threads_counter < 20 then
		begin
			incr threads_counter;

			ignore (Thread.create do_work ());
		end;
		Mutex.unlock counter_mutex;
	done;
	Unix.sleep 100
================================

It checks if thread count is less than 20. If so, new thread is created
and threads_counter incremented. After thread is done, threads_counter
is decremented.

After 5 minutes of work, RSS usage was grown from 3300KB to 5670KB on
FreeBSD 7.0 and from 976KB to 1200KB on Linux. In both cases Ocaml
3.10.2 was used.