On Wed, Feb 08, 2017 at 03:04:21PM +0300, Kirill A. Shutemov wrote: > On Tue, Feb 07, 2017 at 01:44:54PM -0800, Andrew Morton wrote: > > On Tue, 7 Feb 2017 17:33:47 +0300 "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> wrote: > > > > > lock_pte_protection() uses pmd_lock() to make sure that we have stable > > > PTE page table before walking pte range. > > > > > > That's not necessary. We only need to make sure that PTE page table is > > > established. It cannot vanish under us as long as we hold mmap_sem at > > > least for read. > > > > > > And we already have helper for that -- pmd_trans_unstable(). > > > > http://ozlabs.org/~akpm/mmots/broken-out/mm-mprotect-use-pmd_trans_unstable-instead-of-taking-the-pmd_lock.patch > > already did this? > > Right. Except, it doesn't drop unneeded pmd_trans_unstable(pmd) check after > __split_huge_pmd(). > > Could you fold this part of my patch into Andrea's? Reviewed-by: Andrea Arcangeli <aarcange@xxxxxxxxxx> > > diff --git a/mm/mprotect.c b/mm/mprotect.c > index f9c07f54dd62..e919e4613eab 100644 > --- a/mm/mprotect.c > +++ b/mm/mprotect.c > @@ -177,8 +149,6 @@ static inline unsigned long change_pmd_range(struct vm_area_struct *vma, > if (pmd_trans_huge(*pmd) || pmd_devmap(*pmd)) { > if (next - addr != HPAGE_PMD_SIZE) { > __split_huge_pmd(vma, pmd, addr, false, NULL); > - if (pmd_trans_unstable(pmd)) > - continue; > } else { > int nr_ptes = change_huge_pmd(vma, pmd, addr, > newprot, prot_numa); Yes this check was an harmless noop, but it's definitely good to clean up this bit too after the other more important change that has a positive runtime effect, or it could be a source of confusion to the reader if left in there. Thanks! Andrea -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
