Re: [PATCH v3 08/12] mm, swap: simplify swap table sanity range check

[Chris Li <chrisl@kernel.org>]

On Tue, Feb 17, 2026 at 12:06 PM Kairui Song via B4 Relay
<devnull+kasong.tencent.com@kernel.org> wrote:
>
> From: Kairui Song <kasong@tencent.com>
>
> The newly introduced helper, which checks bad slots and emptiness of a
> cluster, can cover the older sanity check just fine, with a more
> rigorous condition check. So merge them.
>
> Signed-off-by: Kairui Song <kasong@tencent.com>

Acked-by: Chris Li <chrisl@kernel.org>

Chris

> ---
>  mm/swapfile.c | 35 +++++++++--------------------------
>  1 file changed, 9 insertions(+), 26 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 18bacf16cd26..9057fb3e4eed 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -459,9 +459,11 @@ static void swap_table_free(struct swap_table *table)
>   * One special case is that bad slots can't be freed, so check the number of
>   * bad slots for swapoff, and non-swapoff path must never free bad slots.
>   */
> -static void swap_cluster_assert_empty(struct swap_cluster_info *ci, bool swapoff)
> +static void swap_cluster_assert_empty(struct swap_cluster_info *ci,
> +                                     unsigned int ci_off, unsigned int nr,
> +                                     bool swapoff)
>  {
> -       unsigned int ci_off = 0, ci_end = SWAPFILE_CLUSTER;
> +       unsigned int ci_end = ci_off + nr;
>         unsigned long swp_tb;
>         int bad_slots = 0;
>
> @@ -588,7 +590,7 @@ static void swap_cluster_schedule_discard(struct swap_info_struct *si,
>
>  static void __free_cluster(struct swap_info_struct *si, struct swap_cluster_info *ci)
>  {
> -       swap_cluster_assert_empty(ci, false);
> +       swap_cluster_assert_empty(ci, 0, SWAPFILE_CLUSTER, false);
>         swap_cluster_free_table(ci);
>         move_cluster(si, ci, &si->free_clusters, CLUSTER_FLAG_FREE);
>         ci->order = 0;
> @@ -898,26 +900,6 @@ static bool cluster_scan_range(struct swap_info_struct *si,
>         return true;
>  }
>
> -/*
> - * Currently, the swap table is not used for count tracking, just
> - * do a sanity check here to ensure nothing leaked, so the swap
> - * table should be empty upon freeing.
> - */
> -static void swap_cluster_assert_table_empty(struct swap_cluster_info *ci,
> -                               unsigned int start, unsigned int nr)
> -{
> -       unsigned int ci_off = start % SWAPFILE_CLUSTER;
> -       unsigned int ci_end = ci_off + nr;
> -       unsigned long swp_tb;
> -
> -       if (IS_ENABLED(CONFIG_DEBUG_VM)) {
> -               do {
> -                       swp_tb = __swap_table_get(ci, ci_off);
> -                       VM_WARN_ON_ONCE(!swp_tb_is_null(swp_tb));
> -               } while (++ci_off < ci_end);
> -       }
> -}
> -
>  static bool cluster_alloc_range(struct swap_info_struct *si,
>                                 struct swap_cluster_info *ci,
>                                 struct folio *folio,
> @@ -943,13 +925,14 @@ static bool cluster_alloc_range(struct swap_info_struct *si,
>         if (likely(folio)) {
>                 order = folio_order(folio);
>                 nr_pages = 1 << order;
> +               swap_cluster_assert_empty(ci, offset % SWAPFILE_CLUSTER, nr_pages, false);
>                 __swap_cache_add_folio(ci, folio, swp_entry(si->type, offset));
>         } else if (IS_ENABLED(CONFIG_HIBERNATION)) {
>                 order = 0;
>                 nr_pages = 1;
>                 WARN_ON_ONCE(si->swap_map[offset]);
>                 si->swap_map[offset] = 1;
> -               swap_cluster_assert_table_empty(ci, offset, 1);
> +               swap_cluster_assert_empty(ci, offset % SWAPFILE_CLUSTER, 1, false);
>         } else {
>                 /* Allocation without folio is only possible with hibernation */
>                 WARN_ON_ONCE(1);
> @@ -1768,7 +1751,7 @@ void swap_entries_free(struct swap_info_struct *si,
>
>         mem_cgroup_uncharge_swap(entry, nr_pages);
>         swap_range_free(si, offset, nr_pages);
> -       swap_cluster_assert_table_empty(ci, offset, nr_pages);
> +       swap_cluster_assert_empty(ci, offset % SWAPFILE_CLUSTER, nr_pages, false);
>
>         if (!ci->count)
>                 free_cluster(si, ci);
> @@ -2780,7 +2763,7 @@ static void free_swap_cluster_info(struct swap_cluster_info *cluster_info,
>                 /* Cluster with bad marks count will have a remaining table */
>                 spin_lock(&ci->lock);
>                 if (rcu_dereference_protected(ci->table, true)) {
> -                       swap_cluster_assert_empty(ci, true);
> +                       swap_cluster_assert_empty(ci, 0, SWAPFILE_CLUSTER, true);
>                         swap_cluster_free_table(ci);
>                 }
>                 spin_unlock(&ci->lock);
>
> --
> 2.52.0
>
>