On Wed, Jan 30, 2019 at 08:44:20PM +0000, Jason Gunthorpe wrote: > Not really, for MRs most drivers care about DMA addresses only. The > only reason struct page ever gets involved is because it is part of > the GUP, SGL and dma_map family of APIs. And the only way you get the DMA address is through the dma mapping APIs. Which except for the little oddball dma_map_resource expect a struct page in some form. And dma_map_resource isn't really up to speed for full blown P2P. Now we could and maybe eventually should change all this. But that is a pre-requisitive for doing anything more fancy, and not something to be hacked around. > O_DIRECT seems to be the justification for struct page, but nobody is > signing up to make O_DIRECT have the required special GUP/SGL/P2P flow > that would be needed to *actually* make that work - so it really isn't > a justification today. O_DIRECT is just the messenger. Anything using GUP will need a struct page, which is all our interfaces that do I/O directly to user pages.
