> I don't know why one ordering is better than the other, but the difference is pretty drastic.
I have the suspicion that some file systems store stat info next to the getdents entries.
Thus cache locality would kick in if you stat a file after receiving it via getdents (and counterintuitively, smaller getdents buffers make it faster then). Also in such cases it would be important to not sort combined getdents outputs before starting (which would destroy the locality again).
I found such a situation with CephFS but don't know what the layout is for common local file systems.
I have the suspicion that some file systems store stat info next to the getdents entries.
Thus cache locality would kick in if you stat a file after receiving it via getdents (and counterintuitively, smaller getdents buffers make it faster then). Also in such cases it would be important to not sort combined getdents outputs before starting (which would destroy the locality again).
I found such a situation with CephFS but don't know what the layout is for common local file systems.