I just upgraded my system RAM from 1 GB (2x 512 MB) to 1.5 GB (512 MB + 1
GB). However, when I boot into a custom compiled kernel (2.6.21-5 with the
tuxonice/suspend2 patch), I see the memory is unchanged (free -m reports
884 MB). When I boot into a vanilla Debian kernel (2.6.21-2), I see the
full 1.5 GB (free -m reports 1510 MB). Needless to say, the BIOS also
reports the full 1.5 GB. I do not remember hardwiring the total memory
anywhere during the compilation of that kernel. Further, the grub boot line
is unremarkable in either case.

The system feels snappier when I use the Debian vanilla kernel (indicating
that it is really seeing more RAM and I do not simply have a kernel
dependent bug in free -m).

Any suggestions to see where things are going awry ?