RE: [PATCH 1/2] sched/wait: Break up long wake list walk

[Liang, Kan]

> On Tue, Aug 22, 2017 at 12:55 PM, Liang, Kan <kan.liang@xxxxxxxxx> wrote:
> >
> >> So I propose testing the attached trivial patch.
> >
> > It doesnât work.
> > The call stack is the same.
> 
> So I would have expected the stack trace to be the same, and I would even
> expect the CPU usage to be fairly similar, because you'd see repeating from
> the callers (taking the fault again if the page is - once again - being migrated).
> 
> But I was hoping that the wait queues would be shorter because the loop for
> the retry would be bigger.
> 
> Oh well.
> 
> I'm slightly out of ideas. Apparently the yield() worked ok (apart from not
> catching all cases), and maybe we could do a version that waits on the page
> bit in the non-contended case, but yields under contention?
> 
> IOW, maybe this is the best we can do for now? Introducing that
> "wait_on_page_migration()" helper might allow us to tweak this a bit as
> people come up with better ideas..

The "wait_on_page_migration()" helper works well in the overnight testing.

Thanks,
Kan

> 
> And then add Tim's patch for the general worst-case just in case?
> 
>              Linus