On Fri, Feb 28, 2025 at 09:59:00AM -0500, Mathieu Desnoyers wrote: > For the VM use-case, I wonder if we could just add a userfaultfd > "COW" event that would notify userspace when a COW happens ? I don't know what's the best for KSM and how well this will work, but we have such event for years.. See UFFDIO_REGISTER_MODE_WP: https://man7.org/linux/man-pages/man2/userfaultfd.2.html > > This would allow userspace to replace ksmd by tracking the age of > those anonymous pages, and issue madvise MADV_MERGE on them to > write-protect+merge them when it is deemed useful. > > With both a new userfaultfd COW event and madvise MADV_MERGE, > is there anything else that is fundamentally missing to move > all the scanning complexity of KSM to userspace for the VM > deduplication use-case ? Thanks, -- Peter Xu
