Message-ID: <174e75a4-f03c-a542-5f6a-651abb5dec58@huawei.com>
Date:   Tue, 7 Mar 2023 09:22:33 +0800
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Subject: Re: [PATCH v2 2/3] mm/damon/paddr: minor refactor of damon_pa_young()
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To:     SeongJae Park <sj@kernel.org>
CC:     Andrew Morton <akpm@linux-foundation.org>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>, <damon@lists.linux.dev>
References: <20230306212727.303846-1-sj@kernel.org>
From:   Kefeng Wang <wangkefeng.wang@huawei.com>
In-Reply-To: <20230306212727.303846-1-sj@kernel.org>
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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.