Re: [PATCH] mm/vmscan: respect cpuset policy during page demotion

Michal Hocko
2022-10-31T09:18:53Z

On Mon 31-10-22 16:51:11, Huang, Ying wrote:
> Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> writes:
>
> > On Fri 28-10-22 07:22:27, Huang, Ying wrote:
> >> Michal Hocko <mhocko-IBi9RG/b67k@public.gmane.org> writes:
> >>
> >> > On Thu 27-10-22 17:31:35, Huang, Ying wrote:
> > [...]
> >> >> I think that it's possible for different processes have different
> >> >> requirements.
> >> >>
> >> >> - Some processes don't care about where the memory is placed, prefer
> >> >> local, then fall back to remote if no free space.
> >> >>
> >> >> - Some processes want to avoid cross-socket traffic, bind to nodes of
> >> >> local socket.
> >> >>
> >> >> - Some processes want to avoid to use slow memory, bind to fast memory
> >> >> node only.
> >> >
> >> > Yes, I do understand that. Do you have any specific examples in mind?
> >> > [...]
> >>
> >> Sorry, I don't have specific examples.
> >
> > OK, then let's stop any complicated solution right here then. Let's
> > start simple with a per-mm flag to disable demotion of an address
> > space.
>
> I'm not a big fan of per-mm flag. Because we don't have users for that
> too and it needs to add ABI too.

OK, if there are no users for opt-out then let's jus document the
current limitations and be done with it.

> > Should there ever be a real demand for a more fine grained solution
> > let's go further but I do not think we want a half baked solution
> > without real usecases.
>
> I'm OK to ignore per-task (and missing per-process) memory policy
> support for now.

I am against such a half baked solution.
--
Michal Hocko
SUSE Labs