Near-zero is a bit loose. It keeps a relatively compact in-memory representation. You’re about right with your estimate. Having measured just now, it’s about 30

Near-zero is a bit loose. It keeps a relatively compact in-memory representation. You’re about right with your estimate. Having measured just now, it’s about 30mb for 1 million directories. The baseline Watcher’s efficiency has a wide spread. When there are many thousands of nested subdirectories, the CPU approaches the limit of the thread it’s on. Flatter directories, or many files without nested subdirectories, do not have nearly as much of an effect. I’ve seen it run on around 10 million paths on a very flat test directory. So, near-zero is somewhat misleading. There’s a wide spread in efficiency. It was my judgement that deeply nested directory trees were far less common in practice then, so I wrote “near-zero” in the optimistic case. It uses polling under the hood (at least, I’m sure it does. It uses whatever std::filesystem uses, which is almost certainly polling).