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

["Huang, Ying" <ying.huang@intel.com>]

Yosry Ahmed <yosryahmed@google.com> writes:

> On Mon, May 22, 2023 at 12:09 AM Huang Ying <ying.huang@intel.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@intel.com>
>> Cc: David Hildenbrand <david@redhat.com>
>> Cc: Hugh Dickins <hughd@google.com>
>> Cc: Johannes Weiner <hannes@cmpxchg.org>
>> Cc: Matthew Wilcox <willy@infradead.org>
>> Cc: Michal Hocko <mhocko@suse.com>
>> Cc: Minchan Kim <minchan@kernel.org>
>> Cc: Tim Chen <tim.c.chen@linux.intel.com>
>> Cc: Yang Shi <shy828301@gmail.com>
>> Cc: Yu Zhao <yuzhao@google.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@google.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