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

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Message-ID: <877cszyg2m.fsf@yhuang6-desk2.ccr.corp.intel.com>
Date:   Tue, 23 May 2023 09:47:13 +0800
From:   "Huang, Ying" <ying.huang@...el.com>
To:     Yosry Ahmed <yosryahmed@...gle.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()

Yosry Ahmed <yosryahmed@...gle.com> writes:

> 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().

It's default behavior to call get/put_swap_device() in the caller for
all almost all swap functions.  I would rather comment the swap
functions needn't to do that, as the comments for
read_swap_cache_async() in [2/5].

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

Thanks!

>>  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]);
>>  }
>>
>>  /*

Best Regards,
Huang, Ying