[ofa-general] New proposal for memory management

[arkady kanevsky]

Matt,What is your feel for FMR like model in user space?
If MPI implementation will do FMR under the covers do you
foresee some issues? It will not be as performant as preregistering
memory once earlier in the MPI program.
Thanks,
Arkady

On Fri, May 1, 2009 at 12:57 PM, Matthew Koop <koop at cse.ohio-state.edu>wrote:

>
> I'm sure sure everyone has gotten this point yet -- It's not a matter of
> the MPIs having this complicated memory registration code in userspace
> they want to push into the kernel to simplify their lives.
>
> The problem is that this registration cache in userspace is a hack that
> can't even be guaranteed. Besides that, this hack ruins many memory
> debugging tools.
>
> This alone is a major hassle for many users since the memory registration
> caching changes the timings. A user can't be told to just run the
> application with the registration cache on for normal runs and then debug
> with it off. Many errors end up being timing dependant.
>
> Matt
>
> On Fri, 1 May 2009, Woodruff, Robert J wrote:
>
> > Jeff wrote,
> >
> > >It sounds like your main objection to fixing them is "it's too much
> > >work."  :-(
> >
> > Not really, in general I think the kernel folks like to keep stuff
> > out of the kernel if it is not really needed, i.e., if it can be
> implemented
> > in user-space, especially really complicated
> > things like this. It is probably a somewhat tricky code to implement,
> prone
> > to bugs that could cause instability in the kernel. Remember if there is
> a bug
> > in user-space and an application dies, it only effects that one
> application,
> > if the bug is in the kernel and it crashes the system it affects
> everyone.
> >
> > That said, if you can find someone to implement it, then do it and send
> in
> > the patches. Assuming the code is not too ugly, maybe it would get
> accepted.
> >
> >
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-- 
Cheers,
Arkady Kanevsky
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