On Sat, Mar 09, 2024 at 05:14:18PM +0100, Christoph Hellwig wrote: > On Fri, Mar 08, 2024 at 04:23:42PM -0400, Jason Gunthorpe wrote: > > > The DMA API callers really need to know what is P2P or not for > > > various reasons. And they should generally have that information > > > available, either from pin_user_pages that needs to special case > > > it or from the in-kernel I/O submitter that build it from P2P and > > > normal memory. > > > > I think that is a BIO thing. RDMA just calls with FOLL_PCI_P2PDMA and > > shoves the resulting page list into in a scattertable. It never checks > > if any returned page is P2P - it has no reason to care. dma_map_sg() > > does all the work. > > Right now it does, but that's not really a good interface. If we have > a pin_user_pages variant that only pins until the next relevant P2P > boundary and tells you about we can significantly simplify the overall > interface. And you will need to have a way to instruct that pin_user_pages() variant to continue anyway, because you asked for FOLL_PCI_P2PDMA. Without that force, you will have !FOLL_PCI_P2PDMA behaviour. When you say "simplify the overall interface", which interface do you mean? Thanks
