Currently, folio_referenced_one() always checks the young flag for each PTE sequentially, which is inefficient for large folios. This inefficiency is especially noticeable when reclaiming clean file-backed large folios, where folio_referenced() is observed as a significant performance hotspot. Moreover, on Arm64 architecture, which supports contiguous PTEs, there is already an optimization to clear the young flags for PTEs within a contiguous range. However, this is not sufficient. We can extend this to perform batched operations for the entire large folio (which might exceed the contiguous range: CONT_PTE_SIZE). Introduce a new API: clear_flush_young_ptes() to facilitate batched checking of the young flags and flushing TLB entries, thereby improving performance during large folio reclamation. And it will be overridden by the architecture that implements a more efficient batch operation in the following patches. Signed-off-by: Baolin Wang --- include/linux/mmu_notifier.h | 9 +++++---- include/linux/pgtable.h | 35 +++++++++++++++++++++++++++++++++++ mm/rmap.c | 29 +++++++++++++++++++++++++++-- 3 files changed, 67 insertions(+), 6 deletions(-) diff --git a/include/linux/mmu_notifier.h b/include/linux/mmu_notifier.h index d1094c2d5fb6..dbbdcef4abf1 100644 --- a/include/linux/mmu_notifier.h +++ b/include/linux/mmu_notifier.h @@ -515,16 +515,17 @@ static inline void mmu_notifier_range_init_owner( range->owner = owner; } -#define ptep_clear_flush_young_notify(__vma, __address, __ptep) \ +#define ptep_clear_flush_young_notify(__vma, __address, __ptep, __nr) \ ({ \ int __young; \ struct vm_area_struct *___vma = __vma; \ unsigned long ___address = __address; \ - __young = ptep_clear_flush_young(___vma, ___address, __ptep); \ + unsigned int ___nr = __nr; \ + __young = clear_flush_young_ptes(___vma, ___address, __ptep, ___nr); \ __young |= mmu_notifier_clear_flush_young(___vma->vm_mm, \ ___address, \ ___address + \ - PAGE_SIZE); \ + ___nr * PAGE_SIZE); \ __young; \ }) @@ -650,7 +651,7 @@ static inline void mmu_notifier_subscriptions_destroy(struct mm_struct *mm) #define mmu_notifier_range_update_to_read_only(r) false -#define ptep_clear_flush_young_notify ptep_clear_flush_young +#define ptep_clear_flush_young_notify clear_flush_young_ptes #define pmdp_clear_flush_young_notify pmdp_clear_flush_young #define ptep_clear_young_notify ptep_test_and_clear_young #define pmdp_clear_young_notify pmdp_test_and_clear_young diff --git a/include/linux/pgtable.h b/include/linux/pgtable.h index 2f0dd3a4ace1..fcf7a7820061 100644 --- a/include/linux/pgtable.h +++ b/include/linux/pgtable.h @@ -1087,6 +1087,41 @@ static inline void wrprotect_ptes(struct mm_struct *mm, unsigned long addr, } #endif +#ifndef clear_flush_young_ptes +/** + * clear_flush_young_ptes - Clear the access bit and perform a TLB flush for PTEs + * that map consecutive pages of the same folio. + * @vma: The virtual memory area the pages are mapped into. + * @addr: Address the first page is mapped at. + * @ptep: Page table pointer for the first entry. + * @nr: Number of entries to clear access bit. + * + * May be overridden by the architecture; otherwise, implemented as a simple + * loop over ptep_clear_flush_young(). + * + * Note that PTE bits in the PTE range besides the PFN can differ. For example, + * some PTEs might be write-protected. + * + * Context: The caller holds the page table lock. The PTEs map consecutive + * pages that belong to the same folio. The PTEs are all in the same PMD. + */ +static inline int clear_flush_young_ptes(struct vm_area_struct *vma, + unsigned long addr, pte_t *ptep, + unsigned int nr) +{ + int young; + + young = ptep_clear_flush_young(vma, addr, ptep); + while (--nr) { + ptep++; + addr += PAGE_SIZE; + young |= ptep_clear_flush_young(vma, addr, ptep); + } + + return young; +} +#endif + /* * On some architectures hardware does not set page access bit when accessing * memory page, it is responsibility of software setting this bit. It brings diff --git a/mm/rmap.c b/mm/rmap.c index d6799afe1114..a0fc05f5966f 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -827,9 +827,11 @@ static bool folio_referenced_one(struct folio *folio, struct folio_referenced_arg *pra = arg; DEFINE_FOLIO_VMA_WALK(pvmw, folio, vma, address, 0); int ptes = 0, referenced = 0; + unsigned int nr; while (page_vma_mapped_walk(&pvmw)) { address = pvmw.address; + nr = 1; if (vma->vm_flags & VM_LOCKED) { ptes++; @@ -874,9 +876,24 @@ static bool folio_referenced_one(struct folio *folio, if (lru_gen_look_around(&pvmw)) referenced++; } else if (pvmw.pte) { + if (folio_test_large(folio)) { + unsigned long end_addr = + pmd_addr_end(address, vma->vm_end); + unsigned int max_nr = + (end_addr - address) >> PAGE_SHIFT; + pte_t pteval = ptep_get(pvmw.pte); + + nr = folio_pte_batch(folio, pvmw.pte, + pteval, max_nr); + } + + ptes += nr; if (ptep_clear_flush_young_notify(vma, address, - pvmw.pte)) + pvmw.pte, nr)) referenced++; + /* Skip the batched PTEs */ + pvmw.pte += nr - 1; + pvmw.address += (nr - 1) * PAGE_SIZE; } else if (IS_ENABLED(CONFIG_TRANSPARENT_HUGEPAGE)) { if (pmdp_clear_flush_young_notify(vma, address, pvmw.pmd)) @@ -886,7 +903,15 @@ static bool folio_referenced_one(struct folio *folio, WARN_ON_ONCE(1); } - pra->mapcount--; + pra->mapcount -= nr; + /* + * If we are sure that we batched the entire folio, + * we can just optimize and stop right here. + */ + if (ptes == pvmw.nr_pages) { + page_vma_mapped_walk_done(&pvmw); + break; + } } if (referenced) -- 2.47.3