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charset="utf-8" HugeTLB address ranges are linearly scanned during fork, unmap and remap operations. If a non-present entry is encountered, the code currently continues to the next huge page aligned address. However, a non-present entry implies that the page table page for that entry is not present. Therefore, the linear scan can skip to the end of range mapped by the page table page. This can speed operations on large sparsely populated hugetlb mappings. Create a new routine hugetlb_mask_last_hp() that will return an address mask. When the mask is ORed with an address, the result will be the address of the last huge page mapped by the associated page table page. Use this mask to update addresses in routines which linearly scan hugetlb address ranges when a non-present pte is encountered. hugetlb_mask_last_hp is related to the implementation of huge_pte_offset as hugetlb_mask_last_hp is called when huge_pte_offset returns NULL. This patch only provides a complete hugetlb_mask_last_hp implementation when CONFIG_ARCH_WANT_GENERAL_HUGETLB is defined. Architectures which provide their own versions of huge_pte_offset can also provide their own version of hugetlb_mask_last_hp. Signed-off-by: Mike Kravetz Reviewed-by: Baolin Wang Tested-by: Baolin Wang --- include/linux/hugetlb.h | 1 + mm/hugetlb.c | 58 +++++++++++++++++++++++++++++++++++++---- 2 files changed, 54 insertions(+), 5 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index e4cff27d1198..25078a0ea1d8 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -194,6 +194,7 @@ pte_t *huge_pte_alloc(struct mm_struct *mm, struct vm_a= rea_struct *vma, unsigned long addr, unsigned long sz); pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz); +unsigned long hugetlb_mask_last_hp(struct hstate *h); int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, unsigned long *addr, pte_t *ptep); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, diff --git a/mm/hugetlb.c b/mm/hugetlb.c index 7c468ac1d069..a2db878b2255 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4731,6 +4731,7 @@ int copy_hugetlb_page_range(struct mm_struct *dst, st= ruct mm_struct *src, unsigned long npages =3D pages_per_huge_page(h); struct address_space *mapping =3D src_vma->vm_file->f_mapping; struct mmu_notifier_range range; + unsigned long last_addr_mask; int ret =3D 0; =20 if (cow) { @@ -4750,11 +4751,14 @@ int copy_hugetlb_page_range(struct mm_struct *dst, = struct mm_struct *src, i_mmap_lock_read(mapping); } =20 + last_addr_mask =3D hugetlb_mask_last_hp(h); for (addr =3D src_vma->vm_start; addr < src_vma->vm_end; addr +=3D sz) { spinlock_t *src_ptl, *dst_ptl; src_pte =3D huge_pte_offset(src, addr, sz); - if (!src_pte) + if (!src_pte) { + addr |=3D last_addr_mask; continue; + } dst_pte =3D huge_pte_alloc(dst, dst_vma, addr, sz); if (!dst_pte) { ret =3D -ENOMEM; @@ -4771,8 +4775,10 @@ int copy_hugetlb_page_range(struct mm_struct *dst, s= truct mm_struct *src, * after taking the lock below. */ dst_entry =3D huge_ptep_get(dst_pte); - if ((dst_pte =3D=3D src_pte) || !huge_pte_none(dst_entry)) + if ((dst_pte =3D=3D src_pte) || !huge_pte_none(dst_entry)) { + addr |=3D last_addr_mask; continue; + } =20 dst_ptl =3D huge_pte_lock(h, dst, dst_pte); src_ptl =3D huge_pte_lockptr(h, src, src_pte); @@ -4933,6 +4939,7 @@ int move_hugetlb_page_tables(struct vm_area_struct *v= ma, unsigned long sz =3D huge_page_size(h); struct mm_struct *mm =3D vma->vm_mm; unsigned long old_end =3D old_addr + len; + unsigned long last_addr_mask; unsigned long old_addr_copy; pte_t *src_pte, *dst_pte; struct mmu_notifier_range range; @@ -4948,12 +4955,16 @@ int move_hugetlb_page_tables(struct vm_area_struct = *vma, flush_cache_range(vma, range.start, range.end); =20 mmu_notifier_invalidate_range_start(&range); + last_addr_mask =3D hugetlb_mask_last_hp(h); /* Prevent race with file truncation */ i_mmap_lock_write(mapping); for (; old_addr < old_end; old_addr +=3D sz, new_addr +=3D sz) { src_pte =3D huge_pte_offset(mm, old_addr, sz); - if (!src_pte) + if (!src_pte) { + old_addr |=3D last_addr_mask; + new_addr |=3D last_addr_mask; continue; + } if (huge_pte_none(huge_ptep_get(src_pte))) continue; =20 @@ -4998,6 +5009,7 @@ static void __unmap_hugepage_range(struct mmu_gather = *tlb, struct vm_area_struct struct hstate *h =3D hstate_vma(vma); unsigned long sz =3D huge_page_size(h); struct mmu_notifier_range range; + unsigned long last_addr_mask; bool force_flush =3D false; =20 WARN_ON(!is_vm_hugetlb_page(vma)); @@ -5018,11 +5030,14 @@ static void __unmap_hugepage_range(struct mmu_gathe= r *tlb, struct vm_area_struct end); adjust_range_if_pmd_sharing_possible(vma, &range.start, &range.end); mmu_notifier_invalidate_range_start(&range); + last_addr_mask =3D hugetlb_mask_last_hp(h); address =3D start; for (; address < end; address +=3D sz) { ptep =3D huge_pte_offset(mm, address, sz); - if (!ptep) + if (!ptep) { + address |=3D last_addr_mask; continue; + } =20 ptl =3D huge_pte_lock(h, mm, ptep); if (huge_pmd_unshare(mm, vma, &address, ptep)) { @@ -6285,6 +6300,7 @@ unsigned long hugetlb_change_protection(struct vm_are= a_struct *vma, unsigned long pages =3D 0, psize =3D huge_page_size(h); bool shared_pmd =3D false; struct mmu_notifier_range range; + unsigned long last_addr_mask; bool uffd_wp =3D cp_flags & MM_CP_UFFD_WP; bool uffd_wp_resolve =3D cp_flags & MM_CP_UFFD_WP_RESOLVE; =20 @@ -6301,12 +6317,15 @@ unsigned long hugetlb_change_protection(struct vm_a= rea_struct *vma, flush_cache_range(vma, range.start, range.end); =20 mmu_notifier_invalidate_range_start(&range); + last_addr_mask =3D hugetlb_mask_last_hp(h); i_mmap_lock_write(vma->vm_file->f_mapping); for (; address < end; address +=3D psize) { spinlock_t *ptl; ptep =3D huge_pte_offset(mm, address, psize); - if (!ptep) + if (!ptep) { + address |=3D last_addr_mask; continue; + } ptl =3D huge_pte_lock(h, mm, ptep); if (huge_pmd_unshare(mm, vma, &address, ptep)) { /* @@ -6857,6 +6876,35 @@ pte_t *huge_pte_offset(struct mm_struct *mm, return (pte_t *)pmd; } =20 +/* + * Return a mask that can be used to update an address to the last huge + * page in a page table page mapping size. Used to skip non-present + * page table entries when linearly scanning address ranges. Architectures + * with unique huge page to page table relationships can define their own + * version of this routine. + */ +unsigned long hugetlb_mask_last_hp(struct hstate *h) +{ + unsigned long hp_size =3D huge_page_size(h); + + if (hp_size =3D=3D P4D_SIZE) + return PGDIR_SIZE - P4D_SIZE; + else if (hp_size =3D=3D PUD_SIZE) + return P4D_SIZE - PUD_SIZE; + else if (hp_size =3D=3D PMD_SIZE) + return PUD_SIZE - PMD_SIZE; + + return ~(0); +} + +#else + +/* See description above. Architectures can provide their own version. */ +__weak unsigned long hugetlb_mask_last_hp(struct hstate *h) +{ + return ~(0); +} + #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */ =20 /* --=20 2.35.3 From nobody Fri May 1 11:12:09 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A8119C433F5 for ; Fri, 27 May 2022 22:59:47 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1353333AbiE0W7p (ORCPT ); Fri, 27 May 2022 18:59:45 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59806 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1355078AbiE0W73 (ORCPT ); Fri, 27 May 2022 18:59:29 -0400 Received: from mx0a-00069f02.pphosted.com (mx0a-00069f02.pphosted.com [205.220.165.32]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id BB5EF13327A for ; 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charset="utf-8" As an optimization for loops sequentially processing hugetlb address ranges, huge_pmd_unshare would update a passed address if it unshared a pmd. Updating a loop control variable outside the loop like this is generally a bad idea. These loops are now using hugetlb_mask_last_hp to optimize scanning when non-present ptes are discovered. The same can be done when huge_pmd_unshare returns 1 indicating a pmd was unshared. Remove address update from huge_pmd_unshare. Change the passed argument type and update all callers. In loops sequentially processing addresses use hugetlb_mask_last_hp to update address if pmd is unshared. Signed-off-by: Mike Kravetz Acked-by: Muchun Song Reviewed-by: Baolin Wang --- include/linux/hugetlb.h | 4 ++-- mm/hugetlb.c | 46 ++++++++++++++++++----------------------- mm/rmap.c | 4 ++-- 3 files changed, 24 insertions(+), 30 deletions(-) diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h index 25078a0ea1d8..307c8f6e6752 100644 --- a/include/linux/hugetlb.h +++ b/include/linux/hugetlb.h @@ -196,7 +196,7 @@ pte_t *huge_pte_offset(struct mm_struct *mm, unsigned long addr, unsigned long sz); unsigned long hugetlb_mask_last_hp(struct hstate *h); int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long *addr, pte_t *ptep); + unsigned long addr, pte_t *ptep); void adjust_range_if_pmd_sharing_possible(struct vm_area_struct *vma, unsigned long *start, unsigned long *end); struct page *follow_huge_addr(struct mm_struct *mm, unsigned long address, @@ -243,7 +243,7 @@ static inline struct address_space *hugetlb_page_mappin= g_lock_write( =20 static inline int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long *addr, pte_t *ptep) + unsigned long addr, pte_t *ptep) { return 0; } diff --git a/mm/hugetlb.c b/mm/hugetlb.c index a2db878b2255..c7d3fbf3ec05 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c @@ -4940,7 +4940,6 @@ int move_hugetlb_page_tables(struct vm_area_struct *v= ma, struct mm_struct *mm =3D vma->vm_mm; unsigned long old_end =3D old_addr + len; unsigned long last_addr_mask; - unsigned long old_addr_copy; pte_t *src_pte, *dst_pte; struct mmu_notifier_range range; bool shared_pmd =3D false; @@ -4968,14 +4967,10 @@ int move_hugetlb_page_tables(struct vm_area_struct = *vma, if (huge_pte_none(huge_ptep_get(src_pte))) continue; =20 - /* old_addr arg to huge_pmd_unshare() is a pointer and so the - * arg may be modified. Pass a copy instead to preserve the - * value in old_addr. - */ - old_addr_copy =3D old_addr; - - if (huge_pmd_unshare(mm, vma, &old_addr_copy, src_pte)) { + if (huge_pmd_unshare(mm, vma, old_addr, src_pte)) { shared_pmd =3D true; + old_addr |=3D last_addr_mask; + new_addr |=3D last_addr_mask; continue; } =20 @@ -5040,10 +5035,11 @@ static void __unmap_hugepage_range(struct mmu_gathe= r *tlb, struct vm_area_struct } =20 ptl =3D huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, &address, ptep)) { + if (huge_pmd_unshare(mm, vma, address, ptep)) { spin_unlock(ptl); tlb_flush_pmd_range(tlb, address & PUD_MASK, PUD_SIZE); force_flush =3D true; + address |=3D last_addr_mask; continue; } =20 @@ -6327,7 +6323,7 @@ unsigned long hugetlb_change_protection(struct vm_are= a_struct *vma, continue; } ptl =3D huge_pte_lock(h, mm, ptep); - if (huge_pmd_unshare(mm, vma, &address, ptep)) { + if (huge_pmd_unshare(mm, vma, address, ptep)) { /* * When uffd-wp is enabled on the vma, unshare * shouldn't happen at all. Warn about it if it @@ -6337,6 +6333,7 @@ unsigned long hugetlb_change_protection(struct vm_are= a_struct *vma, pages++; spin_unlock(ptl); shared_pmd =3D true; + address |=3D last_addr_mask; continue; } pte =3D huge_ptep_get(ptep); @@ -6760,11 +6757,11 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct = vm_area_struct *vma, * 0 the underlying pte page is not shared, or it is the last user */ int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long *addr, pte_t *ptep) + unsigned long addr, pte_t *ptep) { - pgd_t *pgd =3D pgd_offset(mm, *addr); - p4d_t *p4d =3D p4d_offset(pgd, *addr); - pud_t *pud =3D pud_offset(p4d, *addr); + pgd_t *pgd =3D pgd_offset(mm, addr); + p4d_t *p4d =3D p4d_offset(pgd, addr); + pud_t *pud =3D pud_offset(p4d, addr); =20 i_mmap_assert_write_locked(vma->vm_file->f_mapping); BUG_ON(page_count(virt_to_page(ptep)) =3D=3D 0); @@ -6774,14 +6771,6 @@ int huge_pmd_unshare(struct mm_struct *mm, struct vm= _area_struct *vma, pud_clear(pud); put_page(virt_to_page(ptep)); mm_dec_nr_pmds(mm); - /* - * This update of passed address optimizes loops sequentially - * processing addresses in increments of huge page size (PMD_SIZE - * in this case). By clearing the pud, a PUD_SIZE area is unmapped. - * Update address to the 'last page' in the cleared area so that - * calling loop can move to first page past this area. - */ - *addr |=3D PUD_SIZE - PMD_SIZE; return 1; } =20 @@ -6793,7 +6782,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm= _area_struct *vma, } =20 int huge_pmd_unshare(struct mm_struct *mm, struct vm_area_struct *vma, - unsigned long *addr, pte_t *ptep) + unsigned long addr, pte_t *ptep) { return 0; } @@ -6902,6 +6891,13 @@ unsigned long hugetlb_mask_last_hp(struct hstate *h) /* See description above. Architectures can provide their own version. */ __weak unsigned long hugetlb_mask_last_hp(struct hstate *h) { + unsigned long hp_size =3D huge_page_size(h); + +#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE + if (hp_size =3D=3D PMD_SIZE) /* required for pmd sharing */ + return PUD_SIZE - PMD_SIZE; +#endif + return ~(0); } =20 @@ -7128,14 +7124,12 @@ void hugetlb_unshare_all_pmds(struct vm_area_struct= *vma) mmu_notifier_invalidate_range_start(&range); i_mmap_lock_write(vma->vm_file->f_mapping); for (address =3D start; address < end; address +=3D PUD_SIZE) { - unsigned long tmp =3D address; - ptep =3D huge_pte_offset(mm, address, sz); if (!ptep) continue; ptl =3D huge_pte_lock(h, mm, ptep); /* We don't want 'address' to be changed */ - huge_pmd_unshare(mm, vma, &tmp, ptep); + huge_pmd_unshare(mm, vma, address, ptep); spin_unlock(ptl); } flush_hugetlb_tlb_range(vma, start, end); diff --git a/mm/rmap.c b/mm/rmap.c index 5bcb334cd6f2..45b04e2e83ab 100644 --- a/mm/rmap.c +++ b/mm/rmap.c @@ -1559,7 +1559,7 @@ static bool try_to_unmap_one(struct folio *folio, str= uct vm_area_struct *vma, */ VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); =20 - if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) { + if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { flush_tlb_range(vma, range.start, range.end); mmu_notifier_invalidate_range(mm, range.start, range.end); @@ -1923,7 +1923,7 @@ static bool try_to_migrate_one(struct folio *folio, s= truct vm_area_struct *vma, */ VM_BUG_ON(!(flags & TTU_RMAP_LOCKED)); =20 - if (huge_pmd_unshare(mm, vma, &address, pvmw.pte)) { + if (huge_pmd_unshare(mm, vma, address, pvmw.pte)) { flush_tlb_range(vma, range.start, range.end); mmu_notifier_invalidate_range(mm, range.start, range.end); --=20 2.35.3 From nobody Fri May 1 11:12:09 2026 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id A9590C433F5 for ; Fri, 27 May 2022 22:59:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1355098AbiE0W7e (ORCPT ); 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charset="utf-8" Lazy page table copying at fork time was introduced with commit d992895ba2b2 ("Lazy page table copies in fork()"). At the time, hugetlb was very new and did not support page faulting. As a result, it was excluded. When full page fault support was added for hugetlb, the exclusion was not removed. Simply remove the check that prevents lazy copying of hugetlb page tables at fork. Of course, like other mappings this only applies to shared mappings. Lazy page table copying at fork will be less advantageous for hugetlb mappings because: - There are fewer page table entries with hugetlb - hugetlb pmds can be shared instead of copied In any case, completely eliminating the copy at fork time shold speed things up. Signed-off-by: Mike Kravetz Acked-by: David Hildenbrand Acked-by: Muchun Song --- mm/memory.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/mm/memory.c b/mm/memory.c index 21dadf03f089..f390cc11886d 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -1245,7 +1245,7 @@ vma_needs_copy(struct vm_area_struct *dst_vma, struct= vm_area_struct *src_vma) if (userfaultfd_wp(dst_vma)) return true; =20 - if (src_vma->vm_flags & (VM_HUGETLB | VM_PFNMAP | VM_MIXEDMAP)) + if (src_vma->vm_flags & (VM_PFNMAP | VM_MIXEDMAP)) return true; =20 if (src_vma->anon_vma) --=20 2.35.3