Generic IOMMU pooled allocator

[David Miller]

From: cascardo at linux.vnet.ibm.com
Date: Wed, 25 Mar 2015 21:43:42 -0300

> On Mon, Mar 23, 2015 at 10:15:08PM -0400, David Miller wrote:
>> From: Benjamin Herrenschmidt <benh at kernel.crashing.org>
>> Date: Tue, 24 Mar 2015 13:08:10 +1100
>> 
>> > For the large pool, we don't keep a hint so we don't know it's
>> > wrapped, in fact we purposefully don't use a hint to limit
>> > fragmentation on it, but then, it should be used rarely enough that
>> > flushing always is, I suspect, a good option.
>> 
>> I can't think of any use case where the largepool would be hit a lot
>> at all.
> 
> Well, until recently, IOMMU_PAGE_SIZE was 4KiB on Power, so every time a
> driver mapped a whole 64KiB page, it would hit the largepool.

We don't plan to ever use 64KB page size on sparc64, so I think we're
safe there.

There are many reasons using 64KB pages is really stupid, what you
see here with the IOMMU stuff is just one of many symptoms, but I bet
your powerpc guys are kind of sick of hearing it by now... :-)