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

[Michal Hocko <mhocko@kernel.org>]

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.
	 */
-- 
Michal Hocko
SUSE Labs