On Mon, Aug 12, 2019 at 03:22:58PM +0200, Oleg Nesterov wrote: > On 08/12, Kirill A. Shutemov wrote: > > > > On Fri, Aug 09, 2019 at 06:01:18PM +0000, Song Liu wrote: > > > + if (pte_none(*pte) || !pte_present(*pte)) > > > + continue; > > > > You don't need to check both. Present is never none. > > Agreed. > > Kirill, while you are here, shouldn't retract_page_tables() check > vma->anon_vma (and probably do mm_find_pmd) under vm_mm->mmap_sem? > > Can't it race with, say, do_cow_fault? vma->anon_vma can race, but it doesn't matter. False-negative is fine. It's attempt to avoid taking mmap_sem where it can be not productive. mm_find_pmd() cannot race with do_cow_fault() since the page is locked. __do_fault() has to return locked page before we touch page tables. It is somewhat subtle, but I wanted to avoid taking mmap_sem where it is possible. -- Kirill A. Shutemov
