Allowing a process to use more than 4GB RAM

Question

I am running a 64-bit Ubuntu 12.04 on a machine with 8GB RAM. I wrote a C++ program that I compiled with the -m64 (force 64-bit executable) flag in gcc . I checked that the resulting executable is indeed 64-bit.

However, the process caps at using 4GB RAM. How can I allow it to use more?

Edit: output of ulimit -a

ulimit -a
core file size          (blocks, -c) 0

data seg size           (kbytes, -d) unlimited

scheduling priority             (-e) 0

file size               (blocks, -f) unlimited

pending signals                 (-i) 62900

max locked memory       (kbytes, -l) 64

max memory size         (kbytes, -m) unlimited

open files                      (-n) 1024

pipe size            (512 bytes, -p) 8

POSIX message queues     (bytes, -q) 819200

real-time priority              (-r) 0

stack size              (kbytes, -s) 8192

cpu time               (seconds, -t) unlimited

max user processes              (-u) 62900

virtual memory          (kbytes, -v) unlimited

file locks                      (-x) unlimited

Edit 2: link to output of dstat -cdgms --vm

https://www.dropbox.com/s/927s5x6v4bhp4qs/dstat_log.xlsx?dl=0

Answer 1

As best as I can tell, adding the -m64 compilation flag (force 64 bit executable) actually solved my initial problem (app crashing), and what followed was a coincidence that my app actually required so little memory over 4GB (limit for a 32-bit executable) that it showed up as 4GB flat in System Monitor. Thank you to all who contributed, there are a number of things in the comments that might help people trying to diagnose similar issues.