This question already has an answer here:
I'm running Arch Linux, with 8 GB memory and no swap defined.
Sometimes it ran out of memory, then my system get a little bit stuck, and I can see the HDD indicator blinking. Then I restart X, which kills a few memory consumer, and the issue gets solved.
But why would the HDD indicator blink? I have no swap defined / mounted
Maybe the Linux kernel is seeking free spaces with some algorithm? I couldn't find any details about that