Since the RAM disk will be created by a process that is independent of the job itself, the memory usage will not be associated with the session ID or within the cgroups hierarchy. Presumably, you'll need a custom resource (e.g. ramdisk_mb) in order for users to request some amount of RAM disk space, and so that your prologue knows how large a disk to create. You should be able to record this information as resources_used.ramdisk_mb from a hook so that it appears in the accounting string. You may also want to consider creating the RAM disk itself from a hook as opposed to a prologue script if you are comfortable with Python. We would certainly consider adding it to our hooks collection so that others may take advantage of it.