On 11/30/2016 6:23 PM, Jason Gunthorpe wrote: >> and O_DIRECT operations that access GPU memory. > This goes through user space so there is still a VMA.. > >> Also, HMM's migration between two GPUs could use peer to peer in the >> kernel, although that is intended to be handled by the GPU driver if >> I understand correctly. > Hum, presumably these migrations are VMA backed as well... I guess so. >>> Presumably in-kernel could use a vmap or something and the same basic >>> flow? >> I think we can achieve the kernel's needs with ZONE_DEVICE and DMA-API support >> for peer to peer. I'm not sure we need vmap. We need a way to have a scatterlist >> of MMIO pfns, and ZONE_DEVICE allows that. > Well, if there is no virtual map then we are back to how do you do > migrations and other things people seem to want to do on these > pages. Maybe the loose 'struct page' flow is not for those users. I was thinking that kernel use cases would disallow migration, similar to how non-ODP MRs would work. Either they are short-lived (like an O_DIRECT transfer) or they can be longed lived but non-migratable (like perhaps a CMB staging buffer). > But I think if you want kGPU or similar then you probably need vmaps > or something similar to represent the GPU pages in kernel memory. Right, although sometimes the GPU pages are simply inaccessible to the CPU. In any case, I haven't thought about kGPU as a use-case. -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
