Re: [PATCH v17 00/10] mm: introduce memfd_secret system call to create "secret" memory areas

Michal Hocko
2021-02-09T20:08:55Z

On Tue 09-02-21 17:17:22, David Hildenbrand wrote:
> On 09.02.21 14:25, Michal Hocko wrote:
> > On Tue 09-02-21 11:23:35, David Hildenbrand wrote:
> > [...]
> > > I am constantly trying to fight for making more stuff MOVABLE instead of
> > > going into the other direction (e.g., because it's easier to implement,
> > > which feels like the wrong direction).
> > >
> > > Maybe I am the only person that really cares about ZONE_MOVABLE these days
> > > :) I can't stop such new stuff from popping up, so at least I want it to be
> > > documented.
> >
> > MOVABLE zone is certainly an important thing to keep working. And there
> > is still quite a lot of work on the way. But as I've said this is more
> > of a outlier than a norm. On the other hand movable zone is kinda hard
> > requirement for a lot of application and it is to be expected that
> > many features will be less than 100% compatible. Some usecases even
> > impossible. That's why I am arguing that we should have a central
> > document where the movable zone is documented with all the potential
> > problems we have encountered over time and explicitly state which
> > features are fully/partially incompatible.
> >
>
> I'll send a mail during the next weeks to gather current restrictions to
> document them (and include my brain dump). We might see more excessive use
> of ZONE_MOVABLE in the future and as history told us, of CMA as well. We
> really should start documenting/caring.

Excellent! Thanks a lot. I will do my best to help reviewing that.

> @Mike, it would be sufficient for me if one of your patches at least mention
> the situation in the description like
>
> "Please note that secretmem currently behaves much more like long-term GUP
> instead of mlocked memory; secretmem is unmovable memory directly
> consumed/controlled by user space. secretmem cannot be placed onto
> ZONE_MOVABLE/CMA.

Sounds good to me.

--
Michal Hocko
SUSE Labs