File systems are now mounted with the relatime mount option by default, for improved performance.
The relatime mount option stands for relative atime (or time of last access), and relatime will only update the atime if the previous atime is different than the mtime (modification time) or ctime (time of last status change). more info
here is my fstab with already included reatime cat /proc/mounts
/dev/disk/by-uuid/840c4762-57dd-4e43-befc-2047488f30d0 / ext3 rw,relatime,errors=remount-ro,data=ordered 0 0