On Wed, 2023-03-08 at 13:38 -0800, Mike Kravetz wrote:
> On 03/06/23 17:22, Yin Fengwei wrote:
> > It's to prepare the batched rmap update for large folio.
> > No need to looped handle hugetlb. Just handle hugetlb and
> > bail out early.
> >
> > Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
> > ---
> > mm/rmap.c | 200 +++++++++++++++++++++++++++++++++-----------------
> > ----
> > 1 file changed, 121 insertions(+), 79 deletions(-)
>
> Looks good,
>
> Reviewed-by: Mike Kravetz <mike.kravetz@xxxxxxxxxx>
Thanks a lot for reviewing.
>
> A few nits below.
>
> >
> > diff --git a/mm/rmap.c b/mm/rmap.c
> > index ba901c416785..508d141dacc5 100644
> > --- a/mm/rmap.c
> > +++ b/mm/rmap.c
> > @@ -1441,6 +1441,103 @@ void page_remove_rmap(struct page *page,
> > struct vm_area_struct *vma,
> > munlock_vma_folio(folio, vma, compound);
> > }
> >
> > +static bool try_to_unmap_one_hugetlb(struct folio *folio,
> > + struct vm_area_struct *vma, struct
> > mmu_notifier_range range,
> > + struct page_vma_mapped_walk pvmw, unsigned long
> > address,
> > + enum ttu_flags flags)
> > +{
> > + struct mm_struct *mm = vma->vm_mm;
> > + pte_t pteval;
> > + bool ret = true, anon = folio_test_anon(folio);
> > +
> > + /*
> > + * The try_to_unmap() is only passed a hugetlb page
> > + * in the case where the hugetlb page is poisoned.
> > + */
> > + VM_BUG_ON_FOLIO(!folio_test_hwpoison(folio), folio);
> > + /*
> > + * huge_pmd_unshare may unmap an entire PMD page.
> > + * There is no way of knowing exactly which PMDs may
> > + * be cached for this mm, so we must flush them all.
> > + * start/end were already adjusted above to cover this
>
> nit, start/end are adjusted in caller (try_to_unmap_one) not above.
Yes. Will update the comment.
>
> > + * range.
> > + */
> > + flush_cache_range(vma, range.start, range.end);
> > +
> > + /*
> > + * To call huge_pmd_unshare, i_mmap_rwsem must be
> > + * held in write mode. Caller needs to explicitly
> > + * do this outside rmap routines.
> > + *
> > + * We also must hold hugetlb vma_lock in write mode.
> > + * Lock order dictates acquiring vma_lock BEFORE
> > + * i_mmap_rwsem. We can only try lock here and fail
> > + * if unsuccessful.
> > + */
> > + if (!anon) {
> > + VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
> > + if (!hugetlb_vma_trylock_write(vma)) {
> > + ret = false;
> > + goto out;
> > + }
> > + if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) {
> > + hugetlb_vma_unlock_write(vma);
> > + flush_tlb_range(vma,
> > + range.start, range.end);
> > + mmu_notifier_invalidate_range(mm,
> > + range.start, range.end);
> > + /*
> > + * The ref count of the PMD page was
> > + * dropped which is part of the way map
> > + * counting is done for shared PMDs.
> > + * Return 'true' here. When there is
> > + * no other sharing, huge_pmd_unshare
> > + * returns false and we will unmap the
> > + * actual page and drop map count
> > + * to zero.
> > + */
> > + goto out;
> > + }
> > + hugetlb_vma_unlock_write(vma);
> > + }
> > + pteval = huge_ptep_clear_flush(vma, address, pvmw.pte);
> > +
> > + /*
> > + * Now the pte is cleared. If this pte was uffd-wp armed,
> > + * we may want to replace a none pte with a marker pte if
> > + * it's file-backed, so we don't lose the tracking info.
> > + */
> > + pte_install_uffd_wp_if_needed(vma, address, pvmw.pte,
> > pteval);
> > +
> > + /* Set the dirty flag on the folio now the pte is gone. */
> > + if (pte_dirty(pteval))
>
> nit, technically, I suppose this should be huge_pte_dirty but it
> really is
> the same as pte_dirty which is why it works in current code.
Yes. Will update to use huge_pte_dirty().
>
> > + folio_mark_dirty(folio);
> > +
> > + /* Update high watermark before we lower rss */
> > + update_hiwater_rss(mm);
> > +
> > + /* Poisoned hugetlb folio with TTU_HWPOISON always cleared
> > in flags */
> > + pteval = swp_entry_to_pte(make_hwpoison_entry(&folio-
> > >page));
> > + set_huge_pte_at(mm, address, pvmw.pte, pteval);
> > + hugetlb_count_sub(folio_nr_pages(folio), mm);
> > +
> > + /*
> > + * No need to call mmu_notifier_invalidate_range() it has
> > be
> > + * done above for all cases requiring it to happen under
> > page
> > + * table lock before mmu_notifier_invalidate_range_end()
> > + *
> > + * See Documentation/mm/mmu_notifier.rst
> > + */
> > + page_remove_rmap(&folio->page, vma,
> > folio_test_hugetlb(folio));
>
> nit, we KNOW folio_test_hugetlb(folio) is true here so can just pass
> 'true'. In addition, the same call in try_to_unmap_one is now known
> to
> always be false. No need to check folio_test_hugetlb(folio) there as
> well.
The "folio_test_hugetlb(folio) -> true" changes was in patch 3. I tried
to apply "one patch for code moving and one patch for code change)" to
make review easy. But this patch already changed the code, I will move
"folio_test_hugetlb(folio)->true" from patch 3 to this one. Thanks.
Regards
Yin, Fengwei
>
