Re: [PATCH 1/8] mm/vmscan: remove redundant folio_test_swapbacked check when folio is file lru

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

Miaohe Lin <linmiaohe@huawei.com> writes:

> On 2022/3/31 14:37, Huang, Ying wrote:
>> Muchun Song <songmuchun@bytedance.com> writes:
>> 
>>> On Tue, Mar 29, 2022 at 9:26 PM Miaohe Lin <linmiaohe@huawei.com> wrote:
>>>>
>>>> When folio is file lru, folio_test_swapbacked is guaranteed to be true. So
>>>> it's unnecessary to check it here again. No functional change intended.
>>>>
>>>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>>>> ---
>>>>  mm/vmscan.c | 3 +--
>>>>  1 file changed, 1 insertion(+), 2 deletions(-)
>>>>
>>>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>>>> index 1678802e03e7..7c1a9713bfc9 100644
>>>> --- a/mm/vmscan.c
>>>> +++ b/mm/vmscan.c
>>>> @@ -1434,8 +1434,7 @@ static void folio_check_dirty_writeback(struct folio *folio,
>>>>          * Anonymous pages are not handled by flushers and must be written
>>>>          * from reclaim context. Do not stall reclaim based on them
>>>>          */
>>>> -       if (!folio_is_file_lru(folio) ||
>>>> -           (folio_test_anon(folio) && !folio_test_swapbacked(folio))) {
>>>> +       if (!folio_is_file_lru(folio) || folio_test_anon(folio)) {
>>>
>>> At least your login is no problem since folio_is_file_lru() is equal to
>>> !folio_test_swapbacked().  But the new code is not clear to me.
>>> The old code is easy to understand, e.g. folio_test_anon(folio) &&
>>> !folio_test_swapbacked(folio) tells us that the anon pages which
>>> do not need to be swapped should be skipped.
>> 
>> That is for MADV_FREE pages.  The code is introduced in commit
>> 802a3a92ad7a ("mm: reclaim MADV_FREE pages").
>> 
>> So I think the original code is better.  It's an implementation detail
>> that folio_is_file_lru() equals !folio_test_swapbacked().  It may be
>> better to add some comments here for MADV_FREE pages.
>> 
>
> Do you tend to drop this patch or adding a comment with the change in this patch or something else?

I suggest to drop the code change and add a comment about MADV_FREE.

Best Regards,
Huang, Ying

> Thanks.
>
>>> So I'm neutral on the patch.
>> 
>> Best Regards,
>> Huang, Ying
>> .
>>