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

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Date:   Mon, 6 Mar 2023 09:56:49 +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 2023/3/6 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?

Thanks

>>> +    if (need_lock && !folio_trylock(folio))
>>> +        goto out;
>>>       rmap_walk(folio, &rwc);
>>>       if (need_lock)
>>>           folio_unlock(folio);
>>> -    folio_put(folio);
>>> -out:
>>>       *folio_sz = folio_size(folio);
>>> +out:
>>> +    folio_put(folio);
>>
>> Before this change, folio_size() is called after folio_put().  
>> Shouldn't it be
>> called before folio_put()?  If so, could we make a separate fix for 
>> that first,
>> and then make this change on top of it, so that it can be easily 
>> applied to
>> relevant stable kernels?
>>
> Yes， I could separate it, after folio_put(), the folio could be 
> re-allocated and the folio_size calculation is not right.
>>
>> Thanks,
>> SJ
>>
>>>       return accessed;
>>>   }
>>> -- 
>>> 2.35.3
>>>
>>>