linux-kernel - Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa

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Date:   Wed, 8 Mar 2023 09:03:09 +0800
From:   Kefeng Wang <wangkefeng.wang@...wei.com>
To:     SeongJae Park <sj@...nel.org>
CC:     Andrew Morton <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>, <damon@...ts.linux.dev>
Subject: Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa_young()



On 2023/3/8 2:00, SeongJae Park wrote:
> On Tue, 7 Mar 2023 09:22:33 +0800 Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> 
>>
>>
>> On 2023/3/7 5:27, SeongJae Park wrote:
>>> Hi Kefeng,
>>>
>>> On Mon, 6 Mar 2023 09:56:49 +0800 Kefeng Wang <wangkefeng.wang@...wei.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@...wei.com> wrote:
>>>>>>
>>>>>>> Omit three lines by unified folio_put(), and make code more clear.
>>>>>>>
>>>>>>> Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.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.
> 
> Ah, you're right.  Thank you for kind explanation.  I was out of my mind for
> some reason.  Maybe we could just do 'goto out' in the branch.

Yes, will update this patchset with this change.
> 
> 
> Thanks,
> SJ