First of all, even if it worked, I don't think setting up swap on the internal flash is a good idea, due to the read/write lifetime. Swapping on an RS-MMC, though, seems reasonable, since they are replaceable. In fact, I'm using the included MMC for that very purpose, since it's small and I intend to replace it anyway.

Crisis: your reboot issue is likely due to trying to create a swap file that is too large. For some reason, the device reboots if you try to activate too much swap within a certain amount of time. I'm found that sixteen megabytes per fifteen seconds is close to the limit. If you want more than sixteen megs, you need to create two or more swap files and swapon them with fifteen seconds of delay between each swapon. I think twenty-four meg swap files may work, too, but I usually stick with sixteen.