linux-kernel - Re: [rfc] do not place sub-threads on task

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Message-ID: <20090701054016.GA26877@redhat.com>
Date:	Wed, 1 Jul 2009 07:40:16 +0200
From:	Oleg Nesterov <oleg@...hat.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Ratan Nalumasu <rnalumasu@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Vitaly Mayatskikh <vmayatsk@...hat.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [rfc] do not place sub-threads on task_struct->children list

On 06/30, Roland McGrath wrote:
>
> > Currently we add sub-threads to ->real_parent->children list. This
> > buys nothing but slows down do_wait().
> >
> > With this patch ->children contains only main threads (group leaders).
> > The only complication is that forget_original_parent() should iterate
> > over sub-threads by hand.
>
> This seems right to me, though I'll admit I haven't really walked through
> all the exit/reparent paths afresh with this in mind.
>
> Note that this naturally suggests moving ->sibling to signal_struct.  (Of
> course that can come later.)  The abuse of sibling in reparent_leader adds
> a wrinkle to that, but off hand it looks like it could do the same with it
> living in signal_struct with a bit of contortion.

Yes, this change was suggested a long ago.

But in that case forget_original_parent() still has to iterate over all childs
to send ->pdeath_signal and change ->real_parent when we reparent to sub-thread.

> Oh, and what about the de_thread() leader-replacement case?

Ah, good point!

de_thread() should do list_replace_init().

Oleg.

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