Re: Generic IOMMU pooled allocator

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Thu, 2015-03-26 at 16:00 -0700, David Miller wrote:
> From: cascardo@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@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... :-)

Lalalala :-)

Cheers,
Ben.