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Date: Mon, 30 May 2022 23:36:43 +0800
From: Muchun Song <songmuchun@...edance.com>
To: Mike Kravetz <mike.kravetz@...cle.com>
Cc: linux-kernel@...r.kernel.org, linux-mm@...ck.org,
Michal Hocko <mhocko@...e.com>, Peter Xu <peterx@...hat.com>,
Naoya Horiguchi <naoya.horiguchi@...ux.dev>,
James Houghton <jthoughton@...gle.com>,
Mina Almasry <almasrymina@...gle.com>,
"Aneesh Kumar K . V" <aneesh.kumar@...ux.vnet.ibm.com>,
Anshuman Khandual <anshuman.khandual@....com>,
Paul Walmsley <paul.walmsley@...ive.com>,
Christian Borntraeger <borntraeger@...ux.ibm.com>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [RFC PATCH 2/3] hugetlb: do not update address in
huge_pmd_unshare
On Fri, May 27, 2022 at 03:58:48PM -0700, Mike Kravetz wrote:
> 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
Totally agree.
> 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 <mike.kravetz@...cle.com>
Acked-by: Muchun Song <songmuchun@...edance.com>
Some nits below.
> ---
> 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_mapping_lock_write(
>
> 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 *vma,
> struct mm_struct *mm = vma->vm_mm;
> unsigned long old_end = 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 = 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;
>
> - /* 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 = 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 = true;
> + old_addr |= last_addr_mask;
> + new_addr |= last_addr_mask;
> continue;
> }
>
> @@ -5040,10 +5035,11 @@ static void __unmap_hugepage_range(struct mmu_gather *tlb, struct vm_area_struct
> }
>
> ptl = 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 = true;
> + address |= last_addr_mask;
> continue;
> }
>
> @@ -6327,7 +6323,7 @@ unsigned long hugetlb_change_protection(struct vm_area_struct *vma,
> continue;
> }
> ptl = 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_area_struct *vma,
> pages++;
> spin_unlock(ptl);
> shared_pmd = true;
> + address |= last_addr_mask;
> continue;
> }
> pte = 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 = pgd_offset(mm, *addr);
> - p4d_t *p4d = p4d_offset(pgd, *addr);
> - pud_t *pud = pud_offset(p4d, *addr);
> + pgd_t *pgd = pgd_offset(mm, addr);
> + p4d_t *p4d = p4d_offset(pgd, addr);
> + pud_t *pud = pud_offset(p4d, addr);
>
> i_mmap_assert_write_locked(vma->vm_file->f_mapping);
> BUG_ON(page_count(virt_to_page(ptep)) == 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 |= PUD_SIZE - PMD_SIZE;
> return 1;
> }
>
> @@ -6793,7 +6782,7 @@ pte_t *huge_pmd_share(struct mm_struct *mm, struct vm_area_struct *vma,
> }
>
> 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 = huge_page_size(h);
> +
> +#ifdef CONFIG_ARCH_WANT_HUGE_PMD_SHARE
> + if (hp_size == PMD_SIZE) /* required for pmd sharing */
> + return PUD_SIZE - PMD_SIZE;
> +#endif
> +
> return ~(0);
Should be ~0UL (However, this should belong to the previous patch).
> }
>
> @@ -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 = start; address < end; address += PUD_SIZE) {
> - unsigned long tmp = address;
> -
> ptep = huge_pte_offset(mm, address, sz);
> if (!ptep)
> continue;
> ptl = huge_pte_lock(h, mm, ptep);
> /* We don't want 'address' to be changed */
Dead comment, should be removed.
> - 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, struct vm_area_struct *vma,
> */
> VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
>
> - 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, struct vm_area_struct *vma,
> */
> VM_BUG_ON(!(flags & TTU_RMAP_LOCKED));
>
> - 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);
> --
> 2.35.3
>
>
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