Generic IOMMU pooled allocator

[David Miller]

From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
Date: Tue, 24 Mar 2015 09:21:05 +1100

> Dave, what's your feeling there ? Does anybody around still have
> some HW that we can test with ?

I don't see what the actual problem is.

Even if you use multiple pools, which we should for scalability on
sun4u too, just do the flush when allocation in _any_ pool wraps
around.

That's still better than not doing the optimization at all.

That is always going to be correct, and you can use a separate
spinlock to make sure only one thread of control does the full
IOMMU flush at a time.