What is the correct interpretation of the following kernel error message:
[N] swapper: page allocation failure. order:1, mode:0x20
[N] Pid: 0, comm: swapper Not tainted 2.6.x #15
Is the error fatal (similar to an OOM-kill) or is it just a warning message?
It means the kernel tried to allocate memory (2 pages) and failed.
Whether the error was fatal depends on what component was trying to allocate the memory and if it was a temporary problem or constant one.
Perhaps if you gave us more information (the entire error, system state when it happened, how frequent, etc), you would get a better answer.