I am working on a daemon that monitors file events via inotify to trigger various types of events when files are accessed. I have read that watches are a little expensive, because the Kernel is storing the full path name of every file being watched.
How many watches would be too many?
Edit: Mostly, I'm wondering .. have you ever seen a noticeable performance hit, if so, at how many watches did it happen? Yes, I have to monitor / recursively (however its a minimal bootstrapped system).
100 billions trillions gazillions would be too many, probably. Kernel Korner - Intro to inotify mentions “thousands of watches” so at least that number should not be a problem.
You can find the system limits by reading /proc/sys/fs/inotify/max_user_instances (maximum number of inotify "objects") and /proc/sys/fs/inotify/max_user_watches (maximum number of files watched), so if you exceed those numbers, it's too many ;-) The maximum number of watches is usually several tens of thousands or higher - on my system, 262143 - which is probably more than you'd ever need unless you're trying to watch every file in a file system, but you shouldn't be doing that. I would say, just try not to use more inotify watches than you need to, and don't worry about it unless you notice a significant decrease in performance.