Re: [PATCH] mm,page_alloc: PF_WQ_WORKER threads must sleep at should_reclaim_retry().

[Michal Hocko]

On Mon 30-07-18 23:34:23, Tetsuo Handa wrote:
> On 2018/07/30 18:32, Michal Hocko wrote:
[...]
> > This one is waiting for draining and we are in mm_percpu_wq WQ context
> > which has its rescuer so no other activity can block us for ever. So
> > this certainly shouldn't deadlock. It can be dead slow but well, this is
> > what you will get when your shoot your system to death.
> 
> We need schedule_timeout_*() to allow such WQ_MEM_RECLAIM workqueues to wake up. (Tejun,
> is my understanding correct?) Lack of schedule_timeout_*() does block WQ_MEM_RECLAIM
> workqueues forever.

Hmm. This doesn't match my understanding of what WQ_MEM_RECLAIM actually
guarantees. If you are right then the whole thing sounds quite fragile
to me TBH.

Anyway we would at least have an explanation for what you are seeing.
-- 
Michal Hocko
SUSE Labs