i found on mailing list this :
http://maemo.org/pipermail/maemo-dev...er/002029.html
launch theses commands as root :
dd if=/dev/zero of=/media/mmc1/extraswap bs=1024 count=16384
(you must wait a lot for this....)
mkswap /media/mmc1/extraswap 16384
swapon /media/mmc1/extraswap
and it works

i open a lot of window of internet pdf video etc and here is my free memory :
/home/user # free
total used free shared buffers
Mem: 61828 60376 1452 0 20
Swap: 16376 12696 3680
Total: 78204 73072 5132

i've try with 32768 but the nokia reboot... 16Mo more are very good for the nokia but if we can add more...
i think we must add swapon on the startup of the nokia if we want to have it always but i want to test more before doing this...

PS : if you swapoff, it bug and if you plug usb, it bug (when you plug usb, the mmc card is umount...)