linux-kernel - Re: [PATCH v2 3/8] mm: swap: use swap_entries_free() to free swap entry in swap_entry_put

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Message-ID: <CAMgjq7CXxpG0doC9iXAXkq_ozvN43gBbG7UsNk8_PYMvpLABHA@mail.gmail.com>
Date: Wed, 19 Mar 2025 02:08:33 +0800
From: Kairui Song <ryncsn@...il.com>
To: Kemeng Shi <shikemeng@...weicloud.com>
Cc: akpm@...ux-foundation.org, tim.c.chen@...ux.intel.com, linux-mm@...ck.org, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 3/8] mm: swap: use swap_entries_free() to free swap
 entry in swap_entry_put_locked()

On Tue, Mar 18, 2025 at 2:10 PM Kemeng Shi <shikemeng@...weicloud.com> wrote:
>
> In swap_entry_put_locked(), we will set slot to SWAP_HAS_CACHE before
> using swap_entries_free() to do actual swap entry freeing. This
> introduce an unnecessary intermediate state.
> By using swap_entries_free() in swap_entry_put_locked(), we can
> eliminate the need to set slot to SWAP_HAS_CACHE.
> This change would make the behavior of swap_entry_put_locked() more
> consistent with other put() operations which will do actual free work
> after put last reference.
>
> Signed-off-by: Kemeng Shi <shikemeng@...weicloud.com>
> Reviewed-by: Tim Chen <tim.c.chen@...ux.intel.com>
> ---
>  mm/swapfile.c | 23 ++++++++++-------------
>  1 file changed, 10 insertions(+), 13 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 0aa7ce82c013..40e41e514813 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1348,9 +1348,11 @@ static struct swap_info_struct *_swap_info_get(swp_entry_t entry)
>  }
>
>  static unsigned char swap_entry_put_locked(struct swap_info_struct *si,
> -                                          unsigned long offset,
> +                                          struct swap_cluster_info *ci,
> +                                          swp_entry_t entry,
>                                            unsigned char usage)
>  {
> +       unsigned long offset = swp_offset(entry);
>         unsigned char count;
>         unsigned char has_cache;
>
> @@ -1382,7 +1384,7 @@ static unsigned char swap_entry_put_locked(struct swap_info_struct *si,
>         if (usage)
>                 WRITE_ONCE(si->swap_map[offset], usage);
>         else
> -               WRITE_ONCE(si->swap_map[offset], SWAP_HAS_CACHE);
> +               swap_entries_free(si, ci, entry, 1);
>
>         return usage;
>  }
> @@ -1461,9 +1463,7 @@ static unsigned char swap_entry_put(struct swap_info_struct *si,
>         unsigned char usage;
>
>         ci = lock_cluster(si, offset);
> -       usage = swap_entry_put_locked(si, offset, 1);
> -       if (!usage)
> -               swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
> +       usage = swap_entry_put_locked(si, ci, entry, 1);
>         unlock_cluster(ci);
>
>         return usage;
> @@ -1551,8 +1551,8 @@ static void cluster_swap_free_nr(struct swap_info_struct *si,
>
>         ci = lock_cluster(si, offset);
>         do {
> -               if (!swap_entry_put_locked(si, offset, usage))
> -                       swap_entries_free(si, ci, swp_entry(si->type, offset), 1);
> +               swap_entry_put_locked(si, ci, swp_entry(si->type, offset),
> +                                     usage);
>         } while (++offset < end);
>         unlock_cluster(ci);
>  }
> @@ -1596,12 +1596,9 @@ void put_swap_folio(struct folio *folio, swp_entry_t entry)
>         ci = lock_cluster(si, offset);
>         if (swap_only_has_cache(si, offset, size))
>                 swap_entries_free(si, ci, entry, size);
> -       else {
> -               for (int i = 0; i < size; i++, entry.val++) {
> -                       if (!swap_entry_put_locked(si, offset + i, SWAP_HAS_CACHE))
> -                               swap_entries_free(si, ci, entry, 1);
> -               }
> -       }
> +       else
> +               for (int i = 0; i < size; i++, entry.val++)
> +                       swap_entry_put_locked(si, ci, entry, SWAP_HAS_CACHE);

I'd prefer you keep the bracket here for more readability, and maybe
add bracket for the whole if statement, just a tiny nitpick so still:

Reviewed-by: Kairui Song <kasong@...cent.com>

>         unlock_cluster(ci);
>  }

>
> --
> 2.30.0
>