Arithmetic without limitations?
Paul.Zimmermann at loria.fr
Thu Feb 11 13:29:20 CET 2010
> My idea for GMP has long been to make "hierarchical locality" take care
> of it all. A row in in the k-dimensional matrix would fit into L1
> cache, a plane would fit into memory, further dimensions would live in
> swap space (not exlicit files).
I'm not sure this will work. Here is a concrete example, on a Core 2 with
16Gb of RAM and 4Gb of swap. I'm trying to multiply two numbers of 6e9
decimal digits, thus using about 2.5G of memory each.
With GMP 5.0.1, top says:
27123 pzimmerm 20 0 13.9g 10g 436 R 100 66.5 2:48.90 a.out
27123 pzimmerm 20 0 18.7g 15g 436 R 100 96.7 2:57.91 a.out
27123 pzimmerm 20 0 18.7g 15g 160 D 13 98.1 5:32.93 a.out
then I get:
GNU MP: Cannot allocate memory (size=5100535824)
With Fabrice Bellard's "mptest" program (this is a sub-product of TPI that
performs just one multiplication):
% time ./mptest.new -u -m 16G -p /tmp mul -n ntt_crt 6000M
27139 pzimmerm 20 0 14.8g 14g 688 R 100 94.0 2:22.64 mptest.new
27139 pzimmerm 20 0 14.8g 14g 692 R 100 94.2 7:25.22 mptest.new
704.704u 38.254s 13:46.97 89.8% 0+0k 2160+9732216io 11pf+0w
Here I explicitely said that I wanted to use only 16G of RAM (-m 16G), and
that I want to use the disk (-p /tmp) for extra memory needs.
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