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Date: Wed, 09 Feb 2022 10:27:56 -0500
From: Zi Yan <ziy@...dia.com>
To: "Matthew Wilcox (Oracle)" <willy@...radead.org>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 52/75] mm/rmap: Convert try_to_migrate() to folios
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@...radead.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@...dia.com>
--
Best Regards,
Yan, Zi
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