I was wondering whether the noatime mount option implied the nodiratime option; turned out it’s true.

Though mount’s man page (section 8) does not mention anything on the subject:

noatime: Access timestamps are not updated when a file is read nodiratime: Do not update directory inode access times on this filesystem

Mount’s man page (section 2) is clearer:

MS_NOATIME: Do not update access times for (all types of) files on this file system MS_NODIRATIME: Do not update access times for directories on this file system

As a directory is a file, setting noatime implies nodiratime consequently.

This reasoning is confirmed in a mail by Andrew Morton on Aug 5, 2007:

noatime is a superset of nodiratime, btw