I also started getting these recently on two different Macbooks, and I think they were being caused by the screensaver loading a large number of photos up front

I also started getting these recently on two different Macbooks, and I think they were being caused by the screensaver loading a large number of photos up front rather than just when they're needed. I had configured the 'sliding panels' or whatever it's called to use a whole album of about 1000 photos, and noticed that I was getting these weird OOM notices, and when I checked in activity monitor, there didn't seem to be any memory overuse. But I realised it was happening when I was waking my computer from sleep. I reduced it to 100 photos and now I don't see the warnings any more, so my guess is that the screensaver was trying to read all 1000 or so photos into memory at once, which was causing the issues. If you have a photo screensaver, worth checking (possibly also the desktop background).