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

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Message-ID: <Pine.LNX.4.64.0704061013060.6730@woody.linux-foundation.org>
Date:	Fri, 6 Apr 2007 10:16:27 -0700 (PDT)
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Oleg Nesterov <oleg@...sign.ru>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Robin Holt <holt@....com>, Chris Snook <csnook@...hat.com>,
	Ingo Molnar <mingo@...e.hu>, linux-kernel@...r.kernel.org
Subject: Re: init's children list is long and slows reaping children.

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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