File descriptor leak for mmaped files

[jpalus]

I'm running rootless podman container backed by fuse-overlayfs within which I'm running process opening many files one by one, each being mmap()ed and immediately close()d but all mmap() are kept (to be specific that's linking rui314/mold#797). Now it all works fine within host system or in podman container with overlay driver (which I unfortunately cannot use in this particular case) or when files are not mmap()ed, but scenario fails with fuse-overlayfs due to -EMFILE (Too many open files). It appears that mmap() on file results in file descriptor being kept by fuse-overlayfs process even though file is close()d afterwards.

Is this something that can be avoided or is it perhaps shortcoming of fuse filesystems?