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SubjectRe: [PATCH 2/2] powerpc - Make the irq reverse mapping radix tree lockless
On Thu, 04 Sep 2008 12:52:19 +1000 Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Wed, 2008-09-03 at 15:41 +0200, Sebastien Dugue wrote:
> > On Wed, 20 Aug 2008 15:23:01 +1000 Benjamin Herrenschmidt <benh@kernel.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 :-)

OK, then we're on the same line ;-)

>
> > 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 ?

No it won't block and will fail (returns NULL).

> If it fails, it's
> probably catastrophic enough not to care.

Yep, I'd tend to agree with that.

> You can always fallback to linear lookup.

I will have to add that back as there is no more fallback.

> I don't know if it's worth trying to fire off a new
> allocation attempt later, probably not.

I've been pondering with this lately, but I think that adding a linear
lookup fallback should be OK.

Thanks,

Sebastien.

>
> Ben.
>
>
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