> - Quickly identify all user processes mapping a given page. Can be done with /proc/*/pagemap today. Maybe it's not "quick" because it won't use the rmap chains, but is that a serious issue? > - Determine if and where the kernel maps the page, which is also > important given the opportunity to remove guest memory from the kernel > direct map (as discussed at LPC'24). At least x86 already has a kernel page table dumper in debugfs that can be used for this. The value of a second redundant one seems low. > We also plan to extend this functionality to include KVM and IOMMU > page tables in the future. Yes dumpers for those would likely be useful. (at least for the case when one hand is tied behind your back by security policies forbidding /proc/kcore access) > <pagemap> provides an interface to traversing through user page > tables, but the other information cannot be extracted using the > existing interfaces. Like what? You mean the reference counts? /proc/k* doesn't have any reference counts, and no space for full counts, but I suspect usually all you need to know is a few states like (>1, 1, 0, maybe negative) which could be mapped to a few spare kpageflags bits. That said I thought Willy wanted to move a lot of these elsewhere anyways with the folio revolution, so it might be a short lived interface anyways. -Andi
