[PATCH v1 1/4] mm/hmm: HMM API for P2P DMA to device zone pages

[Christoph Hellwig]

On Thu, Oct 17, 2024 at 10:46:44AM -0300, Jason Gunthorpe wrote:
> On Thu, Oct 17, 2024 at 06:12:55AM -0700, Christoph Hellwig wrote:
> > On Thu, Oct 17, 2024 at 10:05:39AM -0300, Jason Gunthorpe wrote:
> > > Broadly I think whatever flow NVMe uses for P2P will apply to ODP as
> > > well.
> > 
> > ODP is a lot simpler than NVMe for P2P actually :(
> 
> What is your thinking there? I'm looking at the latest patches and I
> would expect dma_iova_init() to accept a phys so it can call
> pci_p2pdma_map_type() once for the whole transaction. It is a slow
> operation.

You can't do it for the whole transaction.  Here is my suggestion
for ODP:

http://git.infradead.org/?p=users/hch/misc.git;a=shortlog;h=refs/heads/dma-split-wip

For NVMe I need to figure out a way to split bios on a per P2P
type boundary as we don't have any space to record if something is a bus
mapped address.