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Introduce vma_can_speculate(), which allows speculative handling for VMAs mapping supported file types. From do_handle_mm_fault(), speculative handling will follow through __handle_mm_fault(), handle_pte_fault() and do_fault(). At this point, we expect speculative faults to continue through one of: - do_read_fault(), fully implemented; - do_cow_fault(), which might abort if missing anon vmas, - do_shared_fault(), not implemented yet (would require ->page_mkwrite() changes). vma_can_speculate() provides an early abort for the do_shared_fault() case, limiting the time spent on trying that unimplemented case. Signed-off-by: Michel Lespinasse <michel@lespinasse.org> Link: https://lore.kernel.org/all/20210407014502.24091-31-michel@lespinasse.org/ Conflicts: include/linux/vm_event_item.h mm/vmstat.c 1. SPF_ATTEMPT_FILE is taken from https://lore.kernel.org/all/20210407014502.24091-36-michel@lespinasse.org/ since the patch posted upstream at the time had a different structure with stats for anonymouse and file-backed pagefaults introduced in a separate patch. Bug: 161210518 Signed-off-by: Suren Baghdasaryan <surenb@google.com> Change-Id: I3a28af63b41b649f02f8b73d53f6494ad114ee5a