Re: [GIT PULL] please pull ummunotify

Gleb Natapov
2009-09-11T16:42:47Z

On Fri, Sep 11, 2009 at 03:11:36PM +0900, KOSAKI Motohiro wrote:
> Hi
>
> Thank you explanation.
>
> >
> > > Can I this version already solved fork() + COW issue? if so, could you
> > > please explain what happen at fork. Obviously RDMA point to either parent
> > > or child page, not both. but Corrent COW rule is, first touch process
> > > get copyed page and other process still own original page. I think it's
> > > unpecected behavior form RDMA.
> >
> > No, ummunotify doesn't really help that much with fork() + COW. If a
> > parent forks and then touches pages that are actively in use for RDMA,
> > then of course they get COWed and RDMA goes to the wrong memory (from
> > the point of view of the parent).
>
> So, Can we assume OpenMPI user process doesn't such thing?
>
> Parhaps, madvise(DONTFORK) or vfork() avoid this issue. but I'm not
> sure all program in the world do that.
>
MPI (or is it libibverbs?) marks all registered memory as DONTFORK.

--
Gleb.