Using close to 3GB heap on Linux, 32 bit

Hello, I'm trying to run a program on rather large data (mostly an Inductive.Graph), and finding it will not grow beyond 2GB RAM, as reported by top. An allocation attempted by the runtime failed, with: out of memory (requested 1048576 bytes) This is unfortunate, as the machine has 4GB, and on stock Linux (+/- 2.6.9) a process can allocate close to 3GB (which is achievable with malloc as long as the chunks allocated are about 16MB or smaller). Any suggestions for allowing the program to grow bigger? I've tried various RTS settings, like -M2800M, -A10m, -H2000M (it seems to ignore -H with more than 2000M), but as soon as the program tries to grow beyond 2GB, it errors out. I'm using 6.4.1 (Debian testing) Thanks! alex