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

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Message-ID: <m18xd5amwq.fsf@ebiederm.dsl.xmission.com>
Date:	Fri, 06 Apr 2007 03:10:29 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Oleg Nesterov <oleg@...sign.ru>
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.

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.

For the sgi problem I doubt it is will make a difference but the change
is certainly worth making.

Eric
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