On 15/10/20 00:25, Dan Williams wrote: > Now, with recent device-dax extensions, it > also has a coarse grained memory management system for physical > address-space partitioning and a path for struct-page-less backing for > VMs. What feature gaps remain vs dmemfs, and can those gaps be closed > with incremental improvements to the 2 existing memory-management > systems? If I understand correctly, devm_memremap_pages() on ZONE_DEVICE memory would still create the "struct page" albeit lazily? KVM then would use the usual get_user_pages() path. Looking more closely at the implementation of dmemfs, I don't understand is why dmemfs needs VM_DMEM etc. and cannot provide access to mmap-ed memory using remap_pfn_range and VM_PFNMAP, just like /dev/mem. If it did that KVM would get physical addresses using fixup_user_fault and never need pfn_to_page() or get_user_pages(). I'm not saying that would instantly be an approval, but it would make remove a lot of hooks. Paolo
