Re: [Patch v2 3/3] mm/khugepaged: unify SCAN_PMD_NONE and SCAN_PMD_NULL into SCAN_NO_PTE_TABLE

[Nico Pache <npache@redhat.com>]

On Thu, Nov 13, 2025 at 8:00 PM Wei Yang <richard.weiyang@gmail.com> wrote:
>
> The current hugepage collapse scan results include two separate values,
> SCAN_PMD_NONE and SCAN_PMD_NULL, which are handled identically by
> the consuming code.
>
> To reduce confusion and improve long-term maintenance, this commit
> merges these two functionally equivalent states into a single, clearer
> identifier: SCAN_NO_PTE_TABLE

Nice cleanup!

Reviewed-by: Nico Pache <npache@redhat.com>

>
> Suggested-by: "David Hildenbrand (Red Hat)" <david@kernel.org>
> Signed-off-by: Wei Yang <richard.weiyang@gmail.com>
> ---
>  include/trace/events/huge_memory.h |  3 +--
>  mm/khugepaged.c                    | 23 ++++++++++-------------
>  2 files changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/include/trace/events/huge_memory.h b/include/trace/events/huge_memory.h
> index dd94d14a2427..4cde53b45a85 100644
> --- a/include/trace/events/huge_memory.h
> +++ b/include/trace/events/huge_memory.h
> @@ -10,8 +10,7 @@
>  #define SCAN_STATUS                                                    \
>         EM( SCAN_FAIL,                  "failed")                       \
>         EM( SCAN_SUCCEED,               "succeeded")                    \
> -       EM( SCAN_PMD_NULL,              "pmd_null")                     \
> -       EM( SCAN_PMD_NONE,              "pmd_none")                     \
> +       EM( SCAN_NO_PTE_TABLE,          "no_pte_table")                 \
>         EM( SCAN_PMD_MAPPED,            "page_pmd_mapped")              \
>         EM( SCAN_EXCEED_NONE_PTE,       "exceed_none_pte")              \
>         EM( SCAN_EXCEED_SWAP_PTE,       "exceed_swap_pte")              \
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 2ee5048b764e..40f9d5939aa5 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -30,8 +30,7 @@
>  enum scan_result {
>         SCAN_FAIL,
>         SCAN_SUCCEED,
> -       SCAN_PMD_NULL,
> -       SCAN_PMD_NONE,
> +       SCAN_NO_PTE_TABLE,
>         SCAN_PMD_MAPPED,
>         SCAN_EXCEED_NONE_PTE,
>         SCAN_EXCEED_SWAP_PTE,
> @@ -934,7 +933,7 @@ static inline int check_pmd_state(pmd_t *pmd)
>         pmd_t pmde = pmdp_get_lockless(pmd);
>
>         if (pmd_none(pmde))
> -               return SCAN_PMD_NONE;
> +               return SCAN_NO_PTE_TABLE;
>
>         /*
>          * The folio may be under migration when khugepaged is trying to
> @@ -944,11 +943,11 @@ static inline int check_pmd_state(pmd_t *pmd)
>         if (pmd_is_migration_entry(pmde))
>                 return SCAN_PMD_MAPPED;
>         if (!pmd_present(pmde))
> -               return SCAN_PMD_NULL;
> +               return SCAN_NO_PTE_TABLE;
>         if (pmd_trans_huge(pmde))
>                 return SCAN_PMD_MAPPED;
>         if (pmd_bad(pmde))
> -               return SCAN_PMD_NULL;
> +               return SCAN_NO_PTE_TABLE;
>         return SCAN_SUCCEED;
>  }
>
> @@ -958,7 +957,7 @@ static int find_pmd_or_thp_or_none(struct mm_struct *mm,
>  {
>         *pmd = mm_find_pmd(mm, address);
>         if (!*pmd)
> -               return SCAN_PMD_NULL;
> +               return SCAN_NO_PTE_TABLE;
>
>         return check_pmd_state(*pmd);
>  }
> @@ -1013,7 +1012,7 @@ static int __collapse_huge_page_swapin(struct mm_struct *mm,
>                         pte = pte_offset_map_ro_nolock(mm, pmd, addr, &ptl);
>                         if (!pte) {
>                                 mmap_read_unlock(mm);
> -                               result = SCAN_PMD_NULL;
> +                               result = SCAN_NO_PTE_TABLE;
>                                 goto out;
>                         }
>                 }
> @@ -1187,7 +1186,7 @@ static int collapse_huge_page(struct mm_struct *mm, unsigned long address,
>                                                       &compound_pagelist);
>                 spin_unlock(pte_ptl);
>         } else {
> -               result = SCAN_PMD_NULL;
> +               result = SCAN_NO_PTE_TABLE;
>         }
>
>         if (unlikely(result != SCAN_SUCCEED)) {
> @@ -1270,7 +1269,7 @@ static int hpage_collapse_scan_pmd(struct mm_struct *mm,
>         nodes_clear(cc->alloc_nmask);
>         pte = pte_offset_map_lock(mm, pmd, start_addr, &ptl);
>         if (!pte) {
> -               result = SCAN_PMD_NULL;
> +               result = SCAN_NO_PTE_TABLE;
>                 goto out;
>         }
>
> @@ -1544,8 +1543,7 @@ int collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr,
>         switch (result) {
>         case SCAN_SUCCEED:
>                 break;
> -       case SCAN_PMD_NULL:
> -       case SCAN_PMD_NONE:
> +       case SCAN_NO_PTE_TABLE:
>                 /*
>                  * All pte entries have been removed and pmd cleared.
>                  * Skip all the pte checks and just update the pmd mapping.
> @@ -2832,8 +2830,7 @@ int madvise_collapse(struct vm_area_struct *vma, unsigned long start,
>                         mmap_read_unlock(mm);
>                         goto handle_result;
>                 /* Whitelisted set of results where continuing OK */
> -               case SCAN_PMD_NULL:
> -               case SCAN_PMD_NONE:
> +               case SCAN_NO_PTE_TABLE:
>                 case SCAN_PTE_NON_PRESENT:
>                 case SCAN_PTE_UFFD_WP:
>                 case SCAN_LACK_REFERENCED_PAGE:
> --
> 2.34.1
>