Re: [PATCH v2 3/8] mm: swap: use swap_entries_free() to free swap entry in swap_entry_put_locked()

[Kemeng Shi]

on 3/19/2025 2:08 AM, Kairui Song wrote:
> On Tue, Mar 18, 2025 at 2:10 PM Kemeng Shi <shikemeng@xxxxxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx>
>> Reviewed-by: Tim Chen <tim.c.chen@xxxxxxxxxxxxxxx>
>> ---
>>  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:
Thanks for review. Both ways are acceptable to me. I will keep the
bracket in next version.

Thanks,
Kemeng
> 
> Reviewed-by: Kairui Song <kasong@xxxxxxxxxxx>
> 
>>         unlock_cluster(ci);
>>  }
> 
>>
>> --
>> 2.30.0
>>
>