Hi, Mike, On Tue, Nov 25, 2025 at 08:38:38PM +0200, Mike Rapoport wrote: > From: "Mike Rapoport (Microsoft)" <[email protected]> > > When a VMA is registered with userfaulfd in minor mode, its ->fault() > method should check if a folio exists in the page cache and if yes > ->fault() should call handle_userfault(VM_UFFD_MISSING).
s/MISSING/MINOR/ > > Instead of calling handle_userfault() directly from a specific ->fault() > implementation introduce new fault reason VM_FAULT_UFFD_MINOR that will > notify the core page fault handler that it should call > handle_userfaultfd(VM_UFFD_MISSING) to complete a page fault. Same. > > Replace a call to handle_userfault(VM_UFFD_MISSING) in shmem and use the Same. > new VM_FAULT_UFFD_MINOR there instead. Personally I'd keep the fault path as simple as possible, because that's the more frequently used path (rather than when userfaultfd is armed). I also see it slightly a pity that even with flags introduced, it only solves the MINOR problem, not MISSING. If it's me, I'd simply export handle_userfault().. I confess I still don't know why exporting it is a problem, but maybe I missed something. Only my two cents. Feel free to go with whatever way you prefer. Thanks, -- Peter Xu
