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

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Message-ID: <20070406094413.GA673@tv-sign.ru>
Date:	Fri, 6 Apr 2007 13:44:13 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Robin Holt <holt@....com>, Chris Snook <csnook@...hat.com>,
	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: init's children list is long and slows reaping children.

On 04/06, Eric W. Biederman wrote:
>
> Oleg Nesterov <oleg@...sign.ru> writes:
> 
> > Robin Holt wrote:
> >>
> >> wait_task_zombie() is taking many seconds to get through the list.
> >> For the case of a modprobe, stop_machine creates one thread per cpu
> >> (remember big number). All are parented to init and their exit will
> >> cause wait_task_zombie to scan multiple times most of the way through
> >> this very long list looking for threads which need to be reaped.
> >
> > Could you try this patch
> >
> > 	http://marc.info/?l=linux-kernel&m=117337194209912
> >
> > ?
> >
> > It can't solve the whole problem, but at least an exiting kernel thread
> > won't kick init.
> 
> At first glance your patch looks reasonable.
> 
> Unfortunately it only applies to the rare thread that calls daemonize,
> and not also to kernel/kthread/kthread() which means it will miss many of
> our current kernel threads.

Note that a thread created by kthread_create() has ->parent == "[kthread]",
not /sbin/init (unless it was created before core_initcall). So I don't really
understand how stop_machine() creates the threads parented to init.

> For the sgi problem I doubt it is will make a difference

most probably you are right.

Oleg.

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