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.shute...@linux.intel.com> 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 <aarca...@redhat.com>
>
> 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
