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

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Message-ID: <20070406172720.GA1147@elte.hu>
Date:	Fri, 6 Apr 2007 19:27:20 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Oleg Nesterov <oleg@...sign.ru>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Robin Holt <holt@....com>, Chris Snook <csnook@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: init's children list is long and slows reaping children.

* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

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

i think part of the problem is the legacy that the list is artificially 
unified: tasks that 'will possibly exit' are on the same list as tasks 
that 'have already exited'. If we split it up into its natural data 
structure, having a list of tasks that are there and do not intend to 
exit, plus a separate list of tasks that are exiting and want to notify 
their parent, all this scanning goes away. I can see no real reason for 
this other than legacy - i dont think the semantics of the wait4() API 
force us to scan all those threads.

putting the freshly reaped tasks at the 'head' of the list is just a 
fancy (and incomplete) way of splitting the list up into two lists, and 
i'd advocate a clean split. Just like have have split the ptrace_list 
away from the main list too.

	Ingo
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