linux-kernel - Re: [GIT PULL] please pull ummunotify

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Date:	Fri, 11 Sep 2009 19:42:47 +0300
From:	Gleb Natapov <gleb@...hat.com>
To:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>
Cc:	Roland Dreier <rdreier@...co.com>, torvalds@...ux-foundation.org,
	akpm@...ux-foundation.org, jsquyres@...co.com,
	linux-rdma@...r.kernel.org, general@...ts.openfabrics.org,
	linux-kernel@...r.kernel.org
Subject: Re: [GIT PULL] please pull ummunotify

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.
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