Not enough free swap space to hibernate

[Vincent Arnoux]

Hello the list,
I have 1 GB or RAM and 1 GB of swap. I reboot rarely my laptop, but
instead suspend it to disk. After a few days and intensive use of
RAM/swap (virtual machines essentially), I end up when trying to
hibernate with the message: "Not enough swap".
During hibernation, RAM is being written to swap partition. If there
is not enough space, suspend to disk just fails. How can I force my
swap to be emptied? I could use a swap file, but I read Ubuntu current
kernel can't hibernate using a swap file.

Thanks,
Vincent