linux-kernel - Re: [PATCH -V2 1/5] swap: Remove get/put_swap_device() in __swap

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Date:   Mon, 22 May 2023 18:22:19 -0700
From:   Yosry Ahmed <yosryahmed@...gle.com>
To:     Huang Ying <ying.huang@...el.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, David Hildenbrand <david@...hat.com>,
        Hugh Dickins <hughd@...gle.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Matthew Wilcox <willy@...radead.org>,
        Michal Hocko <mhocko@...e.com>,
        Minchan Kim <minchan@...nel.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Yang Shi <shy828301@...il.com>, Yu Zhao <yuzhao@...gle.com>
Subject: Re: [PATCH -V2 1/5] swap: Remove get/put_swap_device() in __swap_count()

On Mon, May 22, 2023 at 12:09 AM Huang Ying <ying.huang@...el.com> wrote:
>
> __swap_count() is called in do_swap_page() only, which encloses the
> call site with get/put_swap_device() already.
>
> Signed-off-by: "Huang, Ying" <ying.huang@...el.com>
> Cc: David Hildenbrand <david@...hat.com>
> Cc: Hugh Dickins <hughd@...gle.com>
> Cc: Johannes Weiner <hannes@...xchg.org>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Michal Hocko <mhocko@...e.com>
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Tim Chen <tim.c.chen@...ux.intel.com>
> Cc: Yang Shi <shy828301@...il.com>
> Cc: Yu Zhao <yuzhao@...gle.com>
> ---
>  mm/swapfile.c | 10 ++--------
>  1 file changed, 2 insertions(+), 8 deletions(-)
>
> diff --git a/mm/swapfile.c b/mm/swapfile.c
> index 274bbf797480..8419cba9c192 100644
> --- a/mm/swapfile.c
> +++ b/mm/swapfile.c
> @@ -1432,16 +1432,10 @@ void swapcache_free_entries(swp_entry_t *entries, int n)
>

nit: I would add a comment here that the caller needs get/put_swap_device().

Reviewed-by: Yosry Ahmed <yosryahmed@...gle.com>

>  int __swap_count(swp_entry_t entry)
>  {
> -       struct swap_info_struct *si;
> +       struct swap_info_struct *si = swp_swap_info(entry);
>         pgoff_t offset = swp_offset(entry);
> -       int count = 0;
>
> -       si = get_swap_device(entry);
> -       if (si) {
> -               count = swap_count(si->swap_map[offset]);
> -               put_swap_device(si);
> -       }
> -       return count;
> +       return swap_count(si->swap_map[offset]);
>  }
>
>  /*
> --
> 2.39.2
>
>