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

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Message-ID: <09cee859-6510-ed3c-67da-c1452a534460@redhat.com>
Date:   Mon, 22 May 2023 13:54:00 +0200
From:   David Hildenbrand <david@...hat.com>
To:     Huang Ying <ying.huang@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        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 22.05.23 09:09, Huang Ying 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)
>   
>   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]);
>   }
>   
>   /*

That locking was added in eb085574a752 ("mm, swap: fix race between 
swapoff and some swap operations"). Before 2799e77529c ("swap: fix 
do_swap_page() race with swapoff") added the get_swap_device() to 
do_swap_page().

Reviewed-by: David Hildenbrand <david@...hat.com>

-- 
Thanks,

David / dhildenb