That data may have been evicted during a previous moment of higher memory pressure. If it hasn't been needed since, leaving it in swap probably makes more sense than preemptively paging in data that's known to be cold.
Yeah you're right. But now I'm wondering if it preferred writing to swap over evicting the cache at that time... can make sense if the cache is being hit more than the pages it's swapping out.
13GB app usage is also odd. I feel like running the same thing with half the RAM wouldn't really result in like 5GB of swap.
