well, i guess you'd have to have enough memory to hold the whole file. that doesn't matter though, since the worst that can happen is that the kernel will kill any old process when the ram and swap fill up. i've had no swap, and my ram got filled and it killed anything - it picks a number at random and kills it. not very useful, just extreamly annoying - it should kill the process that is eating up all the ram. but now that we can add huge ammounts of swap space, this isn't a big issue anymore. just dd to a file with input from /dev/zero, run swapon, and if the file gets filled reboot so the swapspace isn't used, and trash it.
