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

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Date:   Mon, 6 Mar 2023 09:10:35 +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 2023/3/4 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;
>> -	}
>> +	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
>>
>>