On Fri, Jun 16, 2017 at 05:01:30PM +0530, Aneesh Kumar K.V wrote:
> "Kirill A. Shutemov" <kirill.shutemov@xxxxxxxxxxxxxxx> writes:
>
> > This patch uses modifed pmdp_invalidate(), that return previous value of pmd,
> > to transfer dirty and accessed bits.
> >
> > Signed-off-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
> > ---
> > fs/proc/task_mmu.c | 8 ++++----
> > mm/huge_memory.c | 29 ++++++++++++-----------------
> > 2 files changed, 16 insertions(+), 21 deletions(-)
> >
> > diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> > index f0c8b33d99b1..f2fc1ef5bba2 100644
> > --- a/fs/proc/task_mmu.c
> > +++ b/fs/proc/task_mmu.c
>
> .....
>
> > @@ -1965,7 +1955,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> > page_ref_add(page, HPAGE_PMD_NR - 1);
> > write = pmd_write(*pmd);
> > young = pmd_young(*pmd);
> > - dirty = pmd_dirty(*pmd);
> > soft_dirty = pmd_soft_dirty(*pmd);
> >
> > pmdp_huge_split_prepare(vma, haddr, pmd);
> > @@ -1995,8 +1984,6 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> > if (soft_dirty)
> > entry = pte_mksoft_dirty(entry);
> > }
> > - if (dirty)
> > - SetPageDirty(page + i);
> > pte = pte_offset_map(&_pmd, addr);
> > BUG_ON(!pte_none(*pte));
> > set_pte_at(mm, addr, pte, entry);
> > @@ -2045,7 +2032,15 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
> > * and finally we write the non-huge version of the pmd entry with
> > * pmd_populate.
> > */
> > - pmdp_invalidate(vma, haddr, pmd);
> > + old = pmdp_invalidate(vma, haddr, pmd);
> > +
> > + /*
> > + * Transfer dirty bit using value returned by pmd_invalidate() to be
> > + * sure we don't race with CPU that can set the bit under us.
> > + */
> > + if (pmd_dirty(old))
> > + SetPageDirty(page);
> > +
> > pmd_populate(mm, pmd, pgtable);
> >
> > if (freeze) {
>
>
> Can we invalidate the pmd early here ? ie, do pmdp_invalidate instead of
> pmdp_huge_split_prepare() ?
I think we can. But it means we would block access to the page for longer
than it's necessary on most architectures. I guess it's not a bit deal.
Maybe as separate patch on top of this patchet? Aneesh, would you take
care of this?
--
Kirill A. Shutemov
