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

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Message-Id: <20090630193037.6CCE01C4@magilla.sf.frob.com>
Date:	Tue, 30 Jun 2009 12:30:37 -0700 (PDT)
From:	Roland McGrath <roland@...hat.com>
To:	Oleg Nesterov <oleg@...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

> 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.

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

Thanks,
Roland
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