[Beowulf] large array to run

Peter Skomoroch peter.skomoroch at gmail.com
Thu Dec 13 15:50:28 PST 2007

This reminds me of a similar issue I had.  What approaches do you take for
large dense matrix multiplication in MPI, when the matrices are too large to
fit into cluster memory?  If I hack up something to cache intermediate
results to disk, the IO seems to drag everything to a halt and I'm looking
for a better solution.  I'd like to use some libraries like PETSc, but how
would you work around memory limitations like this (short of building a
bigger cluster)?

> >> I don't speak fortran natively, but isn't that array
> >> approximately 3.6 TB in size?
> >
> > Oops, forgot to put the decimal in the right place.
> >
> > 9915^3 * 8 bits/integer / 1024^3 bytes/GB = 907 GB.
> >
> > It could be done with a 64 bit kernel. Too big for PAE.
> Yeah, if you had a box with several hundred memory slots....
> Which I say only semi-sarcastically.  They sound like they're coming,
> they're coming.  Who knows, maybe they're here and I'm just out of
> touch.
> If it is a sparse matrix, them just maybe one can do something on this
> scale, but otherwise, well, it's like telling mathematica to go and
> compute umpty-something factorial -- it will go out, make a herioc
> effort, use all the free memory in the universe, and die valiantly
> (perhaps taking down your computer with it if the kernel happens to need
> some memory at a critical time when their isn't any).  Large scale
> computation as a DOS attack...

Peter N. Skomoroch
peter.skomoroch at gmail.com
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