Re: [PATCH v3] mm: fix trying to reclaim unevictable lru page when calling madvise_pageout

[zhong jiang <zhongjiang@huawei.com>]

On 2019/11/5 14:33, Michal Hocko wrote:
> On Sat 02-11-19 15:36:55, zhong jiang wrote:
>> On 2019/11/2 2:32, Michal Hocko wrote:
> [...]
>>> But I would really appreciate to add a comment for the BUG_ON and
>>> explain why do we care about PageUnevictable so much when there is an
>>> explicit page_evictable check in the reclaim path. In other words a
>>> short summary of what Johannes explained in
>>> http://lkml.kernel.org/r/20191030193307.GA48128@cmpxchg.org. Maybe in a
>>> separate patch. Care to send one or should I send it?
>> Hi,  Michal
>>
>> Actually,  I am not very clear about the words Johannes had said.   How the race to
>> tirgger, it will result in an PgeMlocked page can be visible in shrink_page_list.
>>
>> Could you elaborate the race in detail further ?
> I would go with the following comment
>
> 	/*
> 	 * Page reclaim can see !page_evictable(), but it must not see pages that
> 	 * have the PageUnevictable lru bit already set. See  __pagevec_lru_add_fn()
> 	 * for more details.
> 	 */
But  the detail still confuses me in __pagevec_lru_add_fn()  to  see PageMlocked  in vmscan :-\ .