Re: [PATCH v1 02/39] mm/rmap: introduce and use hugetlb_remove_rmap()

Ryan Roberts
2023-12-11T16:16:26Z

On 11/12/2023 15:56, David Hildenbrand wrote:
> hugetlb rmap handling differs quite a lot from "ordinary" rmap code.
> For example, hugetlb currently only supports entire mappings, and treats
> any mapping as mapped using a single "logical PTE". Let's move it out
> of the way so we can overhaul our "ordinary" rmap.
> implementation/interface.
>
> Let's introduce and use hugetlb_remove_rmap() and remove the hugetlb
> code from page_remove_rmap(). This effectively removes one check on the
> small-folio path as well.
>
> Note: all possible candidates that need care are page_remove_rmap() that
> pass compound=true.
>
> Reviewed-by: Yin Fengwei <fengwei.yin@intel.com>
> Signed-off-by: David Hildenbrand <david@redhat.com>

Reviewed-by: Ryan Roberts <ryan.roberts@arm.com>

> ---
> include/linux/rmap.h | 5 +++++
> mm/hugetlb.c | 4 ++--
> mm/rmap.c | 17 ++++++++---------
> 3 files changed, 15 insertions(+), 11 deletions(-)
>
> diff --git a/include/linux/rmap.h b/include/linux/rmap.h
> index 0bfea866f39b..d85bd1d4de04 100644
> --- a/include/linux/rmap.h
> +++ b/include/linux/rmap.h
> @@ -213,6 +213,11 @@ void hugetlb_add_anon_rmap(struct folio *, struct vm_area_struct *,
> void hugetlb_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
> unsigned long address);
>
> +static inline void hugetlb_remove_rmap(struct folio *folio)
> +{
> + atomic_dec(&folio->_entire_mapcount);
> +}
> +
> static inline void __page_dup_rmap(struct page *page, bool compound)
> {
> if (compound) {
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 305f3ca1dee6..ef48ae673890 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -5676,7 +5676,7 @@ void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct *vma,
> make_pte_marker(PTE_MARKER_UFFD_WP),
> sz);
> hugetlb_count_sub(pages_per_huge_page(h), mm);
> - page_remove_rmap(page, vma, true);
> + hugetlb_remove_rmap(page_folio(page));
>
> spin_unlock(ptl);
> tlb_remove_page_size(tlb, page, huge_page_size(h));
> @@ -5987,7 +5987,7 @@ static vm_fault_t hugetlb_wp(struct mm_struct *mm, struct vm_area_struct *vma,
>
> /* Break COW or unshare */
> huge_ptep_clear_flush(vma, haddr, ptep);
> - page_remove_rmap(&old_folio->page, vma, true);
> + hugetlb_remove_rmap(old_folio);
> hugetlb_add_new_anon_rmap(new_folio, vma, haddr);
> if (huge_pte_uffd_wp(pte))
> newpte = huge_pte_mkuffd_wp(newpte);
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 80d42c31281a..4e60c1f38eaa 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -1482,13 +1482,6 @@ void page_remove_rmap(struct page *page, struct vm_area_struct *vma,
>
> VM_BUG_ON_PAGE(compound && !PageHead(page), page);
>
> - /* Hugetlb pages are not counted in NR_*MAPPED */
> - if (unlikely(folio_test_hugetlb(folio))) {
> - /* hugetlb pages are always mapped with pmds */
> - atomic_dec(&folio->_entire_mapcount);
> - return;
> - }
> -
> /* Is page being unmapped by PTE? Is this its last map to be removed? */
> if (likely(!compound)) {
> last = atomic_add_negative(-1, &page->_mapcount);
> @@ -1846,7 +1839,10 @@ static bool try_to_unmap_one(struct folio *folio, struct vm_area_struct *vma,
> dec_mm_counter(mm, mm_counter_file(&folio->page));
> }
> discard:
> - page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
> + if (unlikely(folio_test_hugetlb(folio)))
> + hugetlb_remove_rmap(folio);
> + else
> + page_remove_rmap(subpage, vma, false);
> if (vma->vm_flags & VM_LOCKED)
> mlock_drain_local();
> folio_put(folio);
> @@ -2199,7 +2195,10 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma,
> */
> }
>
> - page_remove_rmap(subpage, vma, folio_test_hugetlb(folio));
> + if (unlikely(folio_test_hugetlb(folio)))
> + hugetlb_remove_rmap(folio);
> + else
> + page_remove_rmap(subpage, vma, false);
> if (vma->vm_flags & VM_LOCKED)
> mlock_drain_local();
> folio_put(folio);