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

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Message-ID: <20070406163100.GA554@tv-sign.ru>
Date:	Fri, 6 Apr 2007 20:31:01 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Robin Holt <holt@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Snook <csnook@...hat.com>, Ingo Molnar <mingo@...e.hu>,
	linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

On 04/06, Eric W. Biederman wrote:
>
> Thinking about it I do agree with Linus that two lists sounds like the
> right solution because it ensures we always have O(1) time when
> waiting for a zombie.

Well. I bet this will be painful, and will uglify the code even more.

do_wait() has to iterate over 2 lists, __ptrace_unlink() should check
->exit_state, etc...

>                        I'd like to place the list head for the zombie
> list in the signal_struct and not in the task_struct so our
> performance continues to be O(1) when we have a threaded process.

Sure. It would be nice to move ->children into signal_struct at first.
Except this change breaks (in fact fixes) ->pdeath_signal behaviour.

> The big benefit of the zombie list over your proposed list reordering
> is that waitpid can return immediately when we don't have zombies to
> wait for, but we have lots of children.

TASK_TRACED/TASK_STOPPED ?

Oleg.

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