linux-kernel - Re: [PATCH 2/2] powerpc - Make the irq reverse mapping radix tree lockless

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Date:	Thu, 04 Sep 2008 12:52:19 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Sebastien Dugue <sebastien.dugue@...l.net>
Cc:	linuxppc-dev@...abs.org, linux-kernel@...r.kernel.org,
	linux-rt-users@...r.kernel.org, paulus@...ba.org,
	michael@...erman.id.au, jean-pierre.dion@...l.net,
	gilles.carry@....bull.net, tinytim@...ibm.com, tglx@...utronix.de,
	rostedt@...dmis.org, dwalker@...sta.com
Subject: Re: [PATCH 2/2] powerpc - Make the irq reverse mapping radix tree
	lockless

On Wed, 2008-09-03 at 15:41 +0200, Sebastien Dugue wrote:
> On Wed, 20 Aug 2008 15:23:01 +1000 Benjamin Herrenschmidt <benh@...nel.crashing.org> wrote:
> 
> > BTW. It would be good to try to turn the GFP_ATOMIC into GFP_KERNEL,
> 
>   That would be nice indeed
> 
> > maybe using a semaphore instead of a lock to protect insertion vs.
> > initialisation.
> 
>   a semaphore? are you meaning a mutex? If not, I fail to understand what you're
> implying.

Right, a mutex, bad habit calling those semaphores from the old days :-)

>   Right, that's the problem with this new scheme and I'm still trying
> to find a way to handle memory allocation failures be it for GFP_ATOMIC or
> GFP_KERNEL.
> 
>   I could not think of anything simple so far and I'm open for suggestions.

GFP_KERNEL should not fail, it will just block no ? If it fails, it's
probably catastrophic enough not to care. You can always fallback to
linear lookup. I don't know if it's worth trying to fire off a new
allocation attempt later, probably not.

Ben.


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