Looks like I spoke/coded too soon. The new version had the same behavior, but only after I had begun running a BitTorrent client with a few GBs of files open at once. I see no thrashing unless the BT client is running, so I think the severity should be downgraded to normal or minor/wishlist. I will alter the code so that the filesystem space check occurs without actually opening all the cache files, that might do the trick.