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

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Message-ID: <20070410133808.GA163@tv-sign.ru>
Date:	Tue, 10 Apr 2007 17:38:08 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Robin Holt <holt@....com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Chris Snook <csnook@...hat.com>, linux-kernel@...r.kernel.org,
	Jack Steiner <steiner@...ricas.sgi.com>
Subject: Re: init's children list is long and slows reaping children.

On 04/10, Ingo Molnar wrote:
> 
> * Eric W. Biederman <ebiederm@...ssion.com> wrote:
> 
> > Ingo Molnar <mingo@...e.hu> writes:
> > 
> > > no. Two _completely separate_ lists.
> > >
> > > i.e. a to-be-reaped task will still be on the main list _too_. The 
> > > main list is for all the PID semantics rules. The reap-list is just 
> > > for wait4() processing. The two would be completely separate.
> > 
> > And what pray tell except for heuristics is the list of children used 
> > for?
> 
> on a second thought: the p->children list is needed for the whole 
> child/parent task tree, which is needed for sys_getppid(). The question 
> is, does anything require us to reparent to within the same thread 
> group?

No! That is why I suggest (a long ago, in fact) to move ->children into
->signal_struct. When sub-thread forks, we set ->parent = group_leader.
We don't need forget_original_parent() until the last thead exists. This
also simplify do_wait().

However, this breaks the current ->pdeath_signal behaviour. In fact (and
Eric thinks the same) this _fixes_ this behaviour, but may break things.

Oleg.

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