linux-kernel - Re: [PATCH 2.6.21-rc3-mm2 3/4] futex_requeue

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Message-ID: <46000C8B.1090600@bull.net>
Date:	Tue, 20 Mar 2007 17:32:11 +0100
From:	Pierre Peiffer <pierre.peiffer@...l.net>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	mingo@...e.hu, drepper@...hat.com, linux-kernel@...r.kernel.org,
	Jean-Pierre Dion <jean-pierre.dion@...l.net>
Subject: Re: [PATCH 2.6.21-rc3-mm2 3/4] futex_requeue_pi optimization

Peter Zijlstra a écrit :

> 
> Unfortunately not, nonlinear vmas don't have a linear relation between
> address and offset. What you would need to do is do a linear walk of the
> page tables. But even that might not suffice if nonlinear vmas may form
> a non-injective, surjective mapping.
> 
> /me checks..
> 
> Hmm, yes that seems valid, so in general, this reverse mapping does not
> uniquely exist for non-linear vmas. :-(
> 
> What to do... disallow futexes in nonlinear mappings, 

> store the address in the key?   <<

That seems to be the only solution... :-/

> 
> the vma_prio_tree would be able to give all vmas associated with a
> mapping.
> 

Thanks for your help.

-- 
Pierre
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