Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 23.128.96.18 as permitted sender) client-ip=23.128.96.18;
Subject: Re: [PATCH 5/5] mm/vmscan: fix misleading comment in
 isolate_lru_pages()
To:     Michal Hocko <mhocko@suse.com>
CC:     <akpm@linux-foundation.org>, <hannes@cmpxchg.org>,
        <vbabka@suse.cz>, <axboe@kernel.dk>, <iamjoonsoo.kim@lge.com>,
        <alexs@kernel.org>, <apopple@nvidia.com>, <willy@infradead.org>,
        <minchan@kernel.org>, <david@redhat.com>, <shli@fb.com>,
        <hillf.zj@alibaba-inc.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>
References: <20210710100329.49174-1-linmiaohe@huawei.com>
 <20210710100329.49174-6-linmiaohe@huawei.com>
 <YOvvFaYMBhISeGEI@dhcp22.suse.cz>
From:   Miaohe Lin <linmiaohe@huawei.com>
Message-ID: <ed30bbc5-8438-d399-a9ef-462eda1b6d4e@huawei.com>
Date:   Mon, 12 Jul 2021 19:16:47 +0800
User-Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:78.0) Gecko/20100101
 Thunderbird/78.6.0
MIME-Version: 1.0
In-Reply-To: <YOvvFaYMBhISeGEI@dhcp22.suse.cz>
Content-Type: text/plain; charset="utf-8"
Content-Language: en-US
Content-Transfer-Encoding: 7bit
Precedence: bulk

On 2021/7/12 15:28, Michal Hocko wrote:
> On Sat 10-07-21 18:03:29, Miaohe Lin wrote:
>> We couldn't know whether the page is being freed elsewhere until we failed
>> to increase the page count.
> 
> This is moving a hard to understand comment from one place to another.

If get_page_unless_zero failed, the page could have been freed elsewhere. I think
this looks straightforward but doesn't help a lot. Are you preferring to just
remove this comment ?

Thank you.

> If anything this would benefit from what that elsewhere might be
> typically or simply drop the comment altogether.
> 
>>
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>>  mm/vmscan.c | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/mm/vmscan.c b/mm/vmscan.c
>> index a74760c48bd8..6e26b3c93242 100644
>> --- a/mm/vmscan.c
>> +++ b/mm/vmscan.c
>> @@ -1891,7 +1891,6 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>>  		 */
>>  		scan += nr_pages;
>>  		if (!__isolate_lru_page_prepare(page, mode)) {
>> -			/* It is being freed elsewhere */
>>  			list_move(&page->lru, src);
>>  			continue;
>>  		}
>> @@ -1901,6 +1900,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
>>  		 * page release code relies on it.
>>  		 */
>>  		if (unlikely(!get_page_unless_zero(page))) {
>> +			/* It is being freed elsewhere. */
>>  			list_move(&page->lru, src);
>>  			continue;
>>  		}
>> -- 
>> 2.23.0
>