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.
