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This is > >> usally not hard on the exporting driver side. > >> > >> It costs some memory but then everything works naturally in the IO > >> stack. > >> > >> Your project is interesting and would be a nice improvement, but I > >> also don't entirely understand why you are bothering when the P2PDMA > >> solution is already fully there ready to go... Is something preventing > >> you from creating the P2PDMA pages for your exporting driver? > > > > The exporter driver may have opted out of the P2PDMA struct page path > > (MEMORY_DEVICE_PCI_P2PDMA route). This maybe a design choice to avoid > > the system RAM overhead. Currently you have to pay this tax to use the block stack. It is certainly bad on x86, but for example 64k page size ARM pays only 83MB, for the same configuration. > That is a good argumentation, but the killer argument for DMA-buf to > not use pages (or folios) is that the exported resource is sometimes > not even memory. I don't think anyone is saying that all DMA-buf must use pages, just that if you want to use the MMIO with the *block stack* then a page based approach already exists and is already being used. Usually through VMAs. I'm aware of all the downsides, but this proposal doesn't explain which ones are motivating the work. Is the lack of pre-registration or the tax the main motivation? Jason