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Efficiently determining disk usage of a folder (without starting from scratch every time)

When I use my computer, one question I commonly want to answer for myself is "how much space is being used by the contents of this folder?". Typical file/window managers, IMX, answer this question the same way that Windows does: by recursing over directory contents and summing their logical sizes. This doesn't suit my needs, for three reasons:

* While the logical size of an individual file is interesting to me, a sum of logical sizes is not; I want a sum of physical sizes, because the question is about disk usage.

* It does the calculation (and directory traversal) on the fly, and doesn't show a progress bar or even a clear indication that it's done. Sometimes the file count and size sum will pause for seconds at a time and then start increasing again.

* It's very slow.

I know that I can use `du` at the command line to get physical sizes, and it's clear when `du` is finished because it outputs to the terminal and eventually returns to a terminal prompt. However, it *doesn't solve the performance issue*.

Is there a filesystem that natively caches this information about directories, or well-known software that maintains such a cache - so that if I e.g. check the size of `/home/user`, the size of `/home/user/Desktop` is already known and can be returned instantaneously (as long as the subfolder hasn't been modified in the mean time)? Similarly, caching the result for `/home/user/Desktop` should speed up a later check for `/home/user`, since it wouldn't have to consider the Desktop contents. It would also be nice to have a GUI for such a program.

I thought about making such a program, but I don't want to reinvent the wheel. I'd also be interested if there's any way to make `ext4` filesystems cache this information automatically, even though they don't appear to by default.