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Message-ID: <CAHbLzkpzxs_6t4opKJJ6mGZnHqeJqA3zt74T39y-eyVt57WNhg@mail.gmail.com>
Date: Tue, 24 Oct 2023 10:40:16 -0700
From: Yang Shi <shy828301@...il.com>
To: "Vishal Moola (Oracle)" <vishal.moola@...il.com>
Cc: linux-mm@...ck.org, linux-kernel@...r.kernel.org,
akpm@...ux-foundation.org
Subject: Re: [PATCH v3 5/5] mm/khugepaged: Convert collapse_pte_mapped_thp()
to use folios
On Fri, Oct 20, 2023 at 11:34 AM Vishal Moola (Oracle)
<vishal.moola@...il.com> wrote:
>
> This removes 2 calls to compound_head() and helps convert khugepaged to
> use folios throughout.
>
> Previously, if the address passed to collapse_pte_mapped_thp()
> corresponded to a tail page, the scan would fail immediately. Using
> filemap_lock_folio() we get the corresponding folio back and try to
> operate on the folio instead.
>
> Signed-off-by: Vishal Moola (Oracle) <vishal.moola@...il.com>
Reviewed-by: Yang Shi <shy828301@...il.com>
> ---
> mm/khugepaged.c | 45 ++++++++++++++++++++-------------------------
> 1 file changed, 20 insertions(+), 25 deletions(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 6a7184cd291b..bc2d8ff269c7 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -1477,7 +1477,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> bool notified = false;
> unsigned long haddr = addr & HPAGE_PMD_MASK;
> struct vm_area_struct *vma = vma_lookup(mm, haddr);
> - struct page *hpage;
> + struct folio *folio;
> pte_t *start_pte, *pte;
> pmd_t *pmd, pgt_pmd;
> spinlock_t *pml = NULL, *ptl;
> @@ -1510,19 +1510,14 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> if (userfaultfd_wp(vma))
> return SCAN_PTE_UFFD_WP;
>
> - hpage = find_lock_page(vma->vm_file->f_mapping,
> + folio = filemap_lock_folio(vma->vm_file->f_mapping,
> linear_page_index(vma, haddr));
> - if (!hpage)
> + if (IS_ERR(folio))
> return SCAN_PAGE_NULL;
>
> - if (!PageHead(hpage)) {
> - result = SCAN_FAIL;
> - goto drop_hpage;
> - }
> -
> - if (compound_order(hpage) != HPAGE_PMD_ORDER) {
> + if (folio_order(folio) != HPAGE_PMD_ORDER) {
> result = SCAN_PAGE_COMPOUND;
> - goto drop_hpage;
> + goto drop_folio;
> }
>
> result = find_pmd_or_thp_or_none(mm, haddr, &pmd);
> @@ -1536,13 +1531,13 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> */
> goto maybe_install_pmd;
> default:
> - goto drop_hpage;
> + goto drop_folio;
> }
>
> result = SCAN_FAIL;
> start_pte = pte_offset_map_lock(mm, pmd, haddr, &ptl);
> if (!start_pte) /* mmap_lock + page lock should prevent this */
> - goto drop_hpage;
> + goto drop_folio;
>
> /* step 1: check all mapped PTEs are to the right huge page */
> for (i = 0, addr = haddr, pte = start_pte;
> @@ -1567,7 +1562,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> * Note that uprobe, debugger, or MAP_PRIVATE may change the
> * page table, but the new page will not be a subpage of hpage.
> */
> - if (hpage + i != page)
> + if (folio_page(folio, i) != page)
> goto abort;
> }
>
> @@ -1582,7 +1577,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> * page_table_lock) ptl nests inside pml. The less time we hold pml,
> * the better; but userfaultfd's mfill_atomic_pte() on a private VMA
> * inserts a valid as-if-COWed PTE without even looking up page cache.
> - * So page lock of hpage does not protect from it, so we must not drop
> + * So page lock of folio does not protect from it, so we must not drop
> * ptl before pgt_pmd is removed, so uffd private needs pml taken now.
> */
> if (userfaultfd_armed(vma) && !(vma->vm_flags & VM_SHARED))
> @@ -1606,7 +1601,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> continue;
> /*
> * We dropped ptl after the first scan, to do the mmu_notifier:
> - * page lock stops more PTEs of the hpage being faulted in, but
> + * page lock stops more PTEs of the folio being faulted in, but
> * does not stop write faults COWing anon copies from existing
> * PTEs; and does not stop those being swapped out or migrated.
> */
> @@ -1615,7 +1610,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> goto abort;
> }
> page = vm_normal_page(vma, addr, ptent);
> - if (hpage + i != page)
> + if (folio_page(folio, i) != page)
> goto abort;
>
> /*
> @@ -1634,8 +1629,8 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>
> /* step 3: set proper refcount and mm_counters. */
> if (nr_ptes) {
> - page_ref_sub(hpage, nr_ptes);
> - add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
> + folio_ref_sub(folio, nr_ptes);
> + add_mm_counter(mm, mm_counter_file(&folio->page), -nr_ptes);
> }
>
> /* step 4: remove empty page table */
> @@ -1659,14 +1654,14 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> maybe_install_pmd:
> /* step 5: install pmd entry */
> result = install_pmd
> - ? set_huge_pmd(vma, haddr, pmd, hpage)
> + ? set_huge_pmd(vma, haddr, pmd, &folio->page)
> : SCAN_SUCCEED;
> - goto drop_hpage;
> + goto drop_folio;
> abort:
> if (nr_ptes) {
> flush_tlb_mm(mm);
> - page_ref_sub(hpage, nr_ptes);
> - add_mm_counter(mm, mm_counter_file(hpage), -nr_ptes);
> + folio_ref_sub(folio, nr_ptes);
> + add_mm_counter(mm, mm_counter_file(&folio->page), -nr_ptes);
> }
> if (start_pte)
> pte_unmap_unlock(start_pte, ptl);
> @@ -1674,9 +1669,9 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
> spin_unlock(pml);
> if (notified)
> mmu_notifier_invalidate_range_end(&range);
> -drop_hpage:
> - unlock_page(hpage);
> - put_page(hpage);
> +drop_folio:
> + folio_unlock(folio);
> + folio_put(folio);
> return result;
> }
>
> --
> 2.40.1
>
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