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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 userfaultfd UFFDIO_REGISTER only seems to work if I pass an address resulting from a mmap mapping, but returns EINVAL if I pass a page-aligned address which sits within a private file mapping (e.g. executable data). Also, I notice that do_wp_page() only calls handle_userfault VM_UFFD_WP when vm_fault flags does not have FAULT_FLAG_UNSHARE set. AFAIU, as it stands now userfaultfd would not help tracking COW faults caused by stores to private file mappings. Am I missing something ? Thanks, Mathieu > >> >> 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, > -- Mathieu Desnoyers EfficiOS Inc. https://www.efficios.com