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

Andrew Morton
2007-04-10T01:15:53Z

On Mon, 09 Apr 2007 18:48:54 -0600
ebiederm@xmission.com (Eric W. Biederman) wrote:

> Andrew Morton <akpm@linux-foundation.org> writes:
>
> > 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>
>
>
> >From another piece of this thread.

Yeah, sorry. Without mentioning any names, someone@tv-sign.ru broke the
threading so I came in halfway.

> > > Robin how many kernel thread per cpu are you seeing?
> >
> > 10.
> >
> > FYI, pid 1539 is kthread.
> >
> > a01:~ # ps -ef | egrep "\[.*\/255\]"
> > root 512 1 0 Apr08 ? 00:00:00 [migration/255]
> > root 513 1 0 Apr08 ? 00:00:00 [ksoftirqd/255]
> > root 1281 1 0 Apr08 ? 00:00:02 [events/255]
> > root 2435 1539 0 Apr08 ? 00:00:00 [kblockd/255]
> > root 3159 1539 0 Apr08 ? 00:00:00 [aio/255]
> > root 4007 1539 0 Apr08 ? 00:00:00 [cqueue/255]
> > root 8653 1539 0 Apr08 ? 00:00:00 [ata/255]
> > root 17438 1539 0 Apr08 ? 00:00:00 [xfslogd/255]
> > root 17950 1539 0 Apr08 ? 00:00:00 [xfsdatad/255]
> > root 18426 1539 0 Apr08 ? 00:00:00 [rpciod/255]
>
>
> So it looks like there were about 1500 kernel threads that started up before
> kthread started.
>
> So the kernel threads appear to have init as their parent is because
> they started before kthread for the most part.
>
> At 10 kernel threads per cpu there may be a little bloat but it isn't
> out of control. It is mostly that we are observing the kernel as
> NR_CPUS approaches infinity. 4096 isn't infinity yet but it's easily
> a 1000 fold bigger then most people are used to :)

Yes, I expect we could run init_workqueues() much earlier, from process 0
rather than from process 1. Something _might_ blow up as it often does when
we change startup ordering, but in this case it would be somewhat surprising.