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    SubjectRe: [PATCH 52/75] mm/rmap: Convert try_to_migrate() to folios
    Date
    On 4 Feb 2022, at 14:58, Matthew Wilcox (Oracle) wrote:

    > Convert the callers to pass a folio and the try_to_migrate_one()
    > worker to use a folio throughout. Fixes an assumption that a
    > folio must be <= PMD size.
    >
    > Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
    > ---
    > include/linux/rmap.h | 2 +-
    > mm/huge_memory.c | 4 ++--
    > mm/migrate.c | 12 ++++++----
    > mm/rmap.c | 57 +++++++++++++++++++++++---------------------
    > 4 files changed, 41 insertions(+), 34 deletions(-)
    >
    > diff --git a/include/linux/rmap.h b/include/linux/rmap.h
    > index 66407434c3b5..502439f20d88 100644
    > --- a/include/linux/rmap.h
    > +++ b/include/linux/rmap.h
    > @@ -192,7 +192,7 @@ static inline void page_dup_rmap(struct page *page, bool compound)
    > int folio_referenced(struct folio *, int is_locked,
    > struct mem_cgroup *memcg, unsigned long *vm_flags);
    >
    > -void try_to_migrate(struct page *page, enum ttu_flags flags);
    > +void try_to_migrate(struct folio *folio, enum ttu_flags flags);
    > void try_to_unmap(struct folio *, enum ttu_flags flags);
    >
    > int make_device_exclusive_range(struct mm_struct *mm, unsigned long start,
    > diff --git a/mm/huge_memory.c b/mm/huge_memory.c
    > index 4ea22b7319fd..21676a4afd07 100644
    > --- a/mm/huge_memory.c
    > +++ b/mm/huge_memory.c
    > @@ -2294,8 +2294,8 @@ static void unmap_page(struct page *page)
    > * pages can simply be left unmapped, then faulted back on demand.
    > * If that is ever changed (perhaps for mlock), update remap_page().
    > */
    > - if (PageAnon(page))
    > - try_to_migrate(page, ttu_flags);
    > + if (folio_test_anon(folio))
    > + try_to_migrate(folio, ttu_flags);
    > else
    > try_to_unmap(folio, ttu_flags | TTU_IGNORE_MLOCK);
    >
    > diff --git a/mm/migrate.c b/mm/migrate.c
    > index 766dc67874a1..5dcdd43d983d 100644
    > --- a/mm/migrate.c
    > +++ b/mm/migrate.c
    > @@ -927,6 +927,7 @@ static int move_to_new_page(struct page *newpage, struct page *page,
    > static int __unmap_and_move(struct page *page, struct page *newpage,
    > int force, enum migrate_mode mode)
    > {
    > + struct folio *folio = page_folio(page);
    > int rc = -EAGAIN;
    > bool page_was_mapped = false;
    > struct anon_vma *anon_vma = NULL;
    > @@ -1030,7 +1031,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
    > /* Establish migration ptes */
    > VM_BUG_ON_PAGE(PageAnon(page) && !PageKsm(page) && !anon_vma,
    > page);
    > - try_to_migrate(page, 0);
    > + try_to_migrate(folio, 0);
    > page_was_mapped = true;
    > }
    >
    > @@ -1173,6 +1174,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
    > enum migrate_mode mode, int reason,
    > struct list_head *ret)
    > {
    > + struct folio *src = page_folio(hpage);
    > int rc = -EAGAIN;
    > int page_was_mapped = 0;
    > struct page *new_hpage;
    > @@ -1249,7 +1251,7 @@ static int unmap_and_move_huge_page(new_page_t get_new_page,
    > ttu |= TTU_RMAP_LOCKED;
    > }
    >
    > - try_to_migrate(hpage, ttu);
    > + try_to_migrate(src, ttu);
    > page_was_mapped = 1;
    >
    > if (mapping_locked)
    > @@ -2449,6 +2451,7 @@ static void migrate_vma_unmap(struct migrate_vma *migrate)
    >
    > for (i = 0; i < npages; i++) {
    > struct page *page = migrate_pfn_to_page(migrate->src[i]);
    > + struct folio *folio;
    >
    > if (!page)
    > continue;
    > @@ -2472,8 +2475,9 @@ static void migrate_vma_unmap(struct migrate_vma *migrate)
    > put_page(page);
    > }
    >
    > - if (page_mapped(page))
    > - try_to_migrate(page, 0);
    > + folio = page_folio(page);
    > + if (folio_mapped(folio))
    > + try_to_migrate(folio, 0);
    >
    > if (page_mapped(page) || !migrate_vma_check_page(page)) {
    > if (!is_zone_device_page(page)) {
    > diff --git a/mm/rmap.c b/mm/rmap.c
    > index c598fd667948..4cfac67e328c 100644
    > --- a/mm/rmap.c
    > +++ b/mm/rmap.c
    > @@ -1767,7 +1767,7 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > range.end = vma_address_end(&pvmw);
    > mmu_notifier_range_init(&range, MMU_NOTIFY_CLEAR, 0, vma, vma->vm_mm,
    > address, range.end);
    > - if (PageHuge(page)) {
    > + if (folio_test_hugetlb(folio)) {
    > /*
    > * If sharing is possible, start and end will be adjusted
    > * accordingly.
    > @@ -1781,21 +1781,24 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > #ifdef CONFIG_ARCH_ENABLE_THP_MIGRATION
    > /* PMD-mapped THP migration entry */
    > if (!pvmw.pte) {
    > - VM_BUG_ON_PAGE(PageHuge(page) ||
    > - !PageTransCompound(page), page);
    > + subpage = folio_page(folio,
    > + pmd_pfn(*pvmw.pmd) - folio_pfn(folio));

    Here you removed the assumption that folio is always <= PMD, right?

    In the commit message, maybe the below is better?
    In THP migration code, fixes an assumption that a folio must be <= PMD size.

    > + VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) ||
    > + !folio_test_pmd_mappable(folio), folio);
    >
    > - set_pmd_migration_entry(&pvmw, page);
    > + set_pmd_migration_entry(&pvmw, subpage);
    > continue;
    > }
    > #endif
    >
    > /* Unexpected PMD-mapped THP? */
    > - VM_BUG_ON_PAGE(!pvmw.pte, page);
    > + VM_BUG_ON_FOLIO(!pvmw.pte, folio);
    >
    > - subpage = page - page_to_pfn(page) + pte_pfn(*pvmw.pte);
    > + subpage = folio_page(folio,
    > + pte_pfn(*pvmw.pte) - folio_pfn(folio));
    > address = pvmw.address;
    >
    > - if (PageHuge(page) && !PageAnon(page)) {
    > + if (folio_test_hugetlb(folio) && !folio_test_anon(folio)) {
    > /*
    > * To call huge_pmd_unshare, i_mmap_rwsem must be
    > * held in write mode. Caller needs to explicitly
    > @@ -1833,15 +1836,15 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > flush_cache_page(vma, address, pte_pfn(*pvmw.pte));
    > pteval = ptep_clear_flush(vma, address, pvmw.pte);
    >
    > - /* Move the dirty bit to the page. Now the pte is gone. */
    > + /* Set the dirty flag on the folio now the pte is gone. */
    > if (pte_dirty(pteval))
    > - set_page_dirty(page);
    > + folio_mark_dirty(folio);
    >
    > /* Update high watermark before we lower rss */
    > update_hiwater_rss(mm);
    >
    > - if (is_zone_device_page(page)) {
    > - unsigned long pfn = page_to_pfn(page);
    > + if (folio_is_zone_device(folio)) {
    > + unsigned long pfn = folio_pfn(folio);
    > swp_entry_t entry;
    > pte_t swp_pte;
    >
    > @@ -1877,16 +1880,16 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > * changed when hugepage migrations to device private
    > * memory are supported.
    > */
    > - subpage = page;
    > - } else if (PageHWPoison(page)) {
    > + subpage = &folio->page;
    > + } else if (PageHWPoison(subpage)) {
    > pteval = swp_entry_to_pte(make_hwpoison_entry(subpage));
    > - if (PageHuge(page)) {
    > - hugetlb_count_sub(compound_nr(page), mm);
    > + if (folio_test_hugetlb(folio)) {
    > + hugetlb_count_sub(folio_nr_pages(folio), mm);
    > set_huge_swap_pte_at(mm, address,
    > pvmw.pte, pteval,
    > vma_mmu_pagesize(vma));
    > } else {
    > - dec_mm_counter(mm, mm_counter(page));
    > + dec_mm_counter(mm, mm_counter(&folio->page));
    > set_pte_at(mm, address, pvmw.pte, pteval);
    > }
    >
    > @@ -1901,7 +1904,7 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > * migration) will not expect userfaults on already
    > * copied pages.
    > */
    > - dec_mm_counter(mm, mm_counter(page));
    > + dec_mm_counter(mm, mm_counter(&folio->page));
    > /* We have to invalidate as we cleared the pte */
    > mmu_notifier_invalidate_range(mm, address,
    > address + PAGE_SIZE);
    > @@ -1947,8 +1950,8 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    > *
    > * See Documentation/vm/mmu_notifier.rst
    > */
    > - page_remove_rmap(subpage, PageHuge(page));
    > - put_page(page);
    > + page_remove_rmap(subpage, folio_test_hugetlb(folio));
    > + folio_put(folio);
    > }
    >
    > mmu_notifier_invalidate_range_end(&range);
    > @@ -1958,13 +1961,13 @@ static bool try_to_migrate_one(struct page *page, struct vm_area_struct *vma,
    >
    > /**
    > * try_to_migrate - try to replace all page table mappings with swap entries
    > - * @page: the page to replace page table entries for
    > + * @folio: the folio to replace page table entries for
    > * @flags: action and flags
    > *
    > - * Tries to remove all the page table entries which are mapping this page and
    > - * replace them with special swap entries. Caller must hold the page lock.
    > + * Tries to remove all the page table entries which are mapping this folio and
    > + * replace them with special swap entries. Caller must hold the folio lock.
    > */
    > -void try_to_migrate(struct page *page, enum ttu_flags flags)
    > +void try_to_migrate(struct folio *folio, enum ttu_flags flags)
    > {
    > struct rmap_walk_control rwc = {
    > .rmap_one = try_to_migrate_one,
    > @@ -1981,7 +1984,7 @@ void try_to_migrate(struct page *page, enum ttu_flags flags)
    > TTU_SYNC)))
    > return;
    >
    > - if (is_zone_device_page(page) && !is_device_private_page(page))
    > + if (folio_is_zone_device(folio) && !folio_is_device_private(folio))
    > return;
    >
    > /*
    > @@ -1992,13 +1995,13 @@ void try_to_migrate(struct page *page, enum ttu_flags flags)
    > * locking requirements of exec(), migration skips
    > * temporary VMAs until after exec() completes.
    > */
    > - if (!PageKsm(page) && PageAnon(page))
    > + if (!folio_test_ksm(folio) && folio_test_anon(folio))
    > rwc.invalid_vma = invalid_migration_vma;
    >
    > if (flags & TTU_RMAP_LOCKED)
    > - rmap_walk_locked(page, &rwc);
    > + rmap_walk_locked(&folio->page, &rwc);
    > else
    > - rmap_walk(page, &rwc);
    > + rmap_walk(&folio->page, &rwc);
    > }
    >
    > /*
    > --
    > 2.34.1

    Otherwise, LGTM. Thanks. Reviewed-by: Zi Yan <ziy@nvidia.com>

    --
    Best Regards,
    Yan, Zi
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