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For a PTE-mapped large folio, this repeat calls to ptep clear+flush, the migration entry build and set, folio_remove_rmap_pte() and folio_put(), each re-entering page_vma_mapped_walk() once per base page (256 times for 1M folio). Mirror try_to_unmap_one() to introduce folio_migrate_pte_batch() to detect eligible batch for PTEs mapping conseuctive subpages of a large folios, and convert the whole batch in one shot using the batched helpers. A side-effect of this change is trace_set_migration_pte() will record one event per batched run instead of earlier behavior of one per base page. Signed-off-by: Shivank Garg --- mm/rmap.c | 110 ++++++++++++++++++++++++++++++++++++++++++++++++-------------- 1 file changed, 85 insertions(+), 25 deletions(-) diff --git a/mm/rmap.c b/mm/rmap.c index ef68adba89c4..cfac85f6f68a 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -2586,6 +2586,48 @@ static bool try_to_migrate_hugetlb_one(struct folio *folio, return ret; } +static inline unsigned int folio_migrate_pte_batch(struct folio *folio, + struct page_vma_mapped_walk *pvmw, pte_t pte, + struct page *subpage, bool anon_exclusive) +{ + unsigned long end_addr, addr = pvmw->address; + struct vm_area_struct *vma = pvmw->vma; + unsigned int max_nr, nr, i; + +#ifdef __HAVE_ARCH_UNMAP_ONE + /* Cannot batch unmap if arch_unmap_one() is defined. */ + return 1; +#endif + + if (!folio_test_large(folio)) + return 1; + if (folio_is_zone_device(folio) || folio_test_has_hwpoisoned(folio)) + return 1; + if (pte_unused(pte)) + return 1; + + /* We may only batch within a single VMA and a single page table. */ + end_addr = pmd_addr_end(addr, vma->vm_end); + max_nr = (end_addr - addr) >> PAGE_SHIFT; + /* + * If unmap fails, we need to restore the ptes. To avoid accidentally + * upgrading write permissions for ptes that were not originally writable, + * and to avoid losing the soft-dirty bit, use the appropriate FPB flags. + */ + nr = folio_pte_batch_flags(folio, vma, pvmw->pte, &pte, max_nr, + FPB_RESPECT_WRITE | FPB_RESPECT_SOFT_DIRTY); + + /* Limit possible batch count to a uniform PageAnonExclusive value */ + if (folio_test_anon(folio)) { + for (i = 1; i < nr; i++) + if (PageAnonExclusive(subpage + i) != anon_exclusive) + break; + nr = i; + } + + return nr; +} + /* * @arg: enum ttu_flags will be passed to this argument. * @@ -2602,7 +2644,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, struct page *subpage; struct mmu_notifier_range range; enum ttu_flags flags = (enum ttu_flags)(long)arg; - unsigned long pfn; + unsigned long pfn, end_addr, nr_pages; /* * When racing against e.g. zap_pte_range() on another cpu, @@ -2655,11 +2697,8 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, VM_BUG_ON_FOLIO(folio_test_hugetlb(folio) || !folio_test_pmd_mappable(folio), folio); - if (set_pmd_migration_entry(&pvmw, subpage)) { - ret = false; - page_vma_mapped_walk_done(&pvmw); - break; - } + if (set_pmd_migration_entry(&pvmw, subpage)) + goto walk_abort; continue; #endif } @@ -2685,9 +2724,16 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, anon_exclusive = folio_test_anon(folio) && PageAnonExclusive(subpage); + nr_pages = 1; if (likely(pte_present(pteval))) { - flush_cache_page(vma, address, pfn); - /* Nuke the page table entry. */ + nr_pages = folio_migrate_pte_batch(folio, &pvmw, pteval, + subpage, anon_exclusive); + + end_addr = address + nr_pages * PAGE_SIZE; + flush_cache_range(vma, address, end_addr); + + /* Nuke the page table entries. */ + pteval = get_and_clear_ptes(mm, address, pvmw.pte, nr_pages); if (should_defer_flush(mm, flags)) { /* * We clear the PTE but do not flush so potentially @@ -2697,11 +2743,9 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, * transition on a cached TLB entry is written through * and traps if the PTE is unmapped. */ - pteval = ptep_get_and_clear(mm, address, pvmw.pte); - - set_tlb_ubc_flush_pending(mm, pteval, address, address + PAGE_SIZE); + set_tlb_ubc_flush_pending(mm, pteval, address, end_addr); } else { - pteval = ptep_clear_flush(vma, address, pvmw.pte); + flush_tlb_range(vma, address, end_addr); } if (pte_dirty(pteval)) folio_mark_dirty(folio); @@ -2741,6 +2785,7 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, dec_mm_counter(mm, mm_counter(folio)); } else { pte_t swp_pte; + unsigned int i; /* * arch_unmap_one() is expected to be a NOP on @@ -2748,19 +2793,15 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, * so we'll not check/care. */ if (arch_unmap_one(mm, vma, address, pteval) < 0) { - set_pte_at(mm, address, pvmw.pte, pteval); - ret = false; - page_vma_mapped_walk_done(&pvmw); - break; + set_ptes(mm, address, pvmw.pte, pteval, nr_pages); + goto walk_abort; } - /* See folio_try_share_anon_rmap_pte(): clear PTE first. */ + /* See folio_try_share_anon_rmap_ptes(): clear PTE first. */ if (anon_exclusive && - folio_try_share_anon_rmap_pte(folio, subpage)) { - set_pte_at(mm, address, pvmw.pte, pteval); - ret = false; - page_vma_mapped_walk_done(&pvmw); - break; + folio_try_share_anon_rmap_ptes(folio, subpage, nr_pages)) { + set_ptes(mm, address, pvmw.pte, pteval, nr_pages); + goto walk_abort; } /* @@ -2770,19 +2811,38 @@ static bool try_to_migrate_one(struct folio *folio, struct vm_area_struct *vma, */ swp_pte = make_migration_swp_pte(subpage, pteval, writable, anon_exclusive); - set_pte_at(mm, address, pvmw.pte, swp_pte); trace_set_migration_pte(address, pte_val(swp_pte), folio_order(folio)); + + /* Set nr_pages migration entries, advancing the PFN. */ + for (i = 0; i < nr_pages; i++) { + set_pte_at(mm, address + (unsigned long)i * PAGE_SIZE, + pvmw.pte + i, swp_pte); + swp_pte = pte_next_swp_offset(swp_pte); + } /* * No need to invalidate here it will synchronize on * against the special swap migration pte. */ } - folio_remove_rmap_pte(folio, subpage, vma); + folio_remove_rmap_ptes(folio, subpage, nr_pages, vma); if (vma->vm_flags & VM_LOCKED) mlock_drain_local(); - folio_put(folio); + folio_put_refs(folio, nr_pages); + + /* + * If we batched the entire folio, there is nothing left to + * walk; stop right here. + */ + if (nr_pages == folio_nr_pages(folio)) + goto walk_done; + continue; +walk_abort: + ret = false; +walk_done: + page_vma_mapped_walk_done(&pvmw); + break; } mmu_notifier_invalidate_range_end(&range); -- 2.43.0