Re: + mm-thp-always-specify-disabled-vmas-as-nh-in-smaps.patch added to -mm tree

[Cyrill Gorcunov <gorcunov@gmail.com>]

On Mon, Jan 21, 2019 at 11:21:44AM +0100, Michal Hocko wrote:
...
> > 
> > The patch from David obviously breaks CRIU, and I can't see a nice solution
> > that will work for everybody.
> > 
> > Of course we could add something like 'NH' to /proc/pid/smaps so that 'nh'
> > will work as David's userspace is expecting and 'NH' will represent the
> > state of VmFlags. This is hackish and ugly, though.
> > 
> > In any case, if David's patch is not reverted CRIU needs some way to know
> > if VMA has VM_NOHUGEPAGE set.
> 
> Hmm, there doesn't seem to be any follow up here and the patch is still
> in the mmotm tree AFAICS in mainline-urgent section. I thought it was
> clarified that the patch will break an existing userspace that relies on
> the documented semantic.
> 
> While it is unfortunate that the use case mentioned by David got broken
> we have provided a long term sustainable which is much better than
> relying on an undocumented side effect of the prctl implementation at
> the time.
> 
> So can we make a decision on this finally please?

As to me David's userspace application could use /proc/$pid/status
to fetch precise THP state. And the patch in mm queue simply breaks
others userspace thus should be reverted.