Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa_young()

Kefeng Wang
2023-03-07T01:23:19Z

On 2023/3/7 5:27, SeongJae Park wrote:
> Hi Kefeng,
>
> On Mon, 6 Mar 2023 09:56:49 +0800 Kefeng Wang <wangkefeng.wang@huawei.com> wrote:
>
>>
>>
>> On 2023/3/6 9:10, Kefeng Wang wrote:
>>>
>>>
>>> On 2023/3/4 2:39, SeongJae Park wrote:
>>>> Hi Kefeng,
>>>>
>>>> On Fri, 3 Mar 2023 16:43:42 +0800 Kefeng Wang
>>>> <wangkefeng.wang@huawei.com> wrote:
>>>>
>>>>> Omit three lines by unified folio_put(), and make code more clear.
>>>>>
>>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
>>>>> ---
>>>>> mm/damon/paddr.c | 11 ++++-------
>>>>> 1 file changed, 4 insertions(+), 7 deletions(-)
>>>>>
>>>>> diff --git a/mm/damon/paddr.c b/mm/damon/paddr.c
>>>>> index 3fda00a0f786..2ef9db0189ca 100644
>>>>> --- a/mm/damon/paddr.c
>>>>> +++ b/mm/damon/paddr.c
>>>>> @@ -130,24 +130,21 @@ static bool damon_pa_young(unsigned long paddr,
>>>>> unsigned long *folio_sz)
>>>>> accessed = false;
>>>>> else
>>>>> accessed = true;
>>>>> - folio_put(folio);
>>>>> goto out;
>>>>
>>>> Because you moved 'out' label to not include *folio_sz setting,
>>>> folio_sz will
>>>> not set in this case. It should be set.
>>> oh, it should be fixed.
>>>>
>>>>> }
>>>>> need_lock = !folio_test_anon(folio) || folio_test_ksm(folio);
>>>>> - if (need_lock && !folio_trylock(folio)) {
>>>>> - folio_put(folio);
>>>>> - return false;
>>>>> - }
>>
>> Hi SJ, apart from above issue, it looks that this branch need the
>> folio_size() setting, right?
>
> folio_sz is effectively used by caller of damon_pa_young() only if this
> function returns true, so this branch doesn't need to set folio_sz.

__damon_pa_check_access() store last_addr, last_accessed and
last_folio_sz, even damon_pa_young() return false, the following check
still use last_folio_sz,

ALIGN_DOWN(last_addr, last_folio_sz) == ALIGN_DOWN(r->sampling_addr,
last_folio_sz)

but last_folio_sz is not up to date, so I think it need to update, and
update last_folio_sz is harmless, which could let's unify the return
path, correct me if I am wrong.