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

On Thu, 04 Sep 2008 12:52:19 +1000 Benjamin Herrenschmidt [off-list ref] wrote:

On Wed, 2008-09-03 at 15:41 +0200, Sebastien Dugue wrote:

quoted

On Wed, 20 Aug 2008 15:23:01 +1000 Benjamin Herrenschmidt [off-list ref] wrote:

quoted

BTW. It would be good to try to turn the GFP_ATOMIC into GFP_KERNEL,

  That would be nice indeed

quoted

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 ;-)

quoted

  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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