Re: init's children list is long and slows reaping children.

Andrew Morton
2007-04-10T00:24:00Z

On Fri, 06 Apr 2007 18:38:40 -0400
Jeff Garzik <jeff@garzik.org> wrote:

> Robin Holt wrote:
> > We have been testing a new larger configuration and we are seeing a very
> > large scan time of init's tsk->children list. In the cases we are seeing,
> > there are numerous kernel processes created for each cpu (ie: events/0
> > ... events/ , xfslogd/0 ... xfslogd/ ). These are
> > all on the list ahead of the processes we are currently trying to reap.
>
> What about attacking the explosion of kernel threads?
>
> As CPU counts increase, the number of per-CPU kernel threads gets really
> ridiculous.
>
> I would rather change the implementation under the hood to start per-CPU
> threads on demand, similar to a thread-pool implementation.
>
> Boxes with $BigNum CPUs probably won't ever use half of those threads.

I suspect there are quite a few kernel threads which don't really need to
be threads at all: the code would quite happily work if it was changed to
use keventd, via schedule_work() and friends. But kernel threads are
somewhat easier to code for.

I also suspect that there are a number of workqueue threads which
could/should have used create_singlethread_workqueue(). Often this is
because the developer just didn't think to do it.

otoh, a lot of these inefficeincies are probably down in scruffy drivers
rather than in core or top-level code.

<I also wonder where all these parented-by-init,
presumably-not-using-kthread kernel threads are coming from>