[ofa-general] Re: [patch 5/6] mmu_notifier: Support for drivers with revers maps (f.e. for XPmem)

[Robin Holt]

On Tue, Feb 26, 2008 at 07:52:41PM +1100, Nick Piggin wrote:
> On Tuesday 26 February 2008 18:21, Gleb Natapov wrote:
> > On Tue, Feb 26, 2008 at 05:11:32PM +1100, Nick Piggin wrote:
> > > > You are missing one point here.  The MPI specifications that have
> > > > been out there for decades do not require the process use a library
> > > > for allocating the buffer.  I realize that is a horrible shortcoming,
> > > > but that is the world we live in.  Even if we could change that spec,
> > >
> > > Can you change the spec?
> >
> > Not really. It will break all existing codes.
> 
> I meant as in eg. submit changes to MPI-3
> 
> 
> > MPI-2 provides a call for 
> > memory allocation (and it's beneficial to use this call for some
> > interconnects), but many (most?) applications are still written for MPI-1
> > and those that are written for MPI-2 mostly uses the old habit of
> > allocating memory by malloc(), or even use stack or BSS memory for
> > communication buffer purposes.
> 
> OK, so MPI-2 already has some way to do that... I'm not saying that we
> can now completely dismiss the idea of using notifiers for this, but it
> is just a good data point to know.

It is in MPI-2, but MPI-2 does not prohibit communication from regions
not allocated by the MPI call.

Thanks,
Robin