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

[Linus Torvalds <torvalds@linux-foundation.org>]

On Fri, 6 Apr 2007, Oleg Nesterov wrote:
> 
> Oops. I misread stop_machine(), it does kernel_thread(), not kthread_create().
> So "stopmachine" threads are all re-parented to init when the caller exits.
> I think it makes sense to set ->exit_state = -1 in stopmachine(), regadless
> of any other changes.

I agree that "->exit_state = -1" makes sense, but I disagree in that I 
don't think it *matters*.

Most of the problematic kernel threads are long-running (as in "never 
exit"). Things like eventd, khelper, migration-threads etc will have init 
as their parent and never actually exit, so their ->exit_state doesn't 
matter. What matters is that they are on the children list, so when you 
have 1024 CPU's, and init has many thousand of these per-cpu threads as 
its children, then the *user* threads (that do exit) will cause problems!

I'd almost prefer to just not add kernel threads to any parent process 
list *at*all*. 

		Linus
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