adding discard options to ext4 on SSD is not a good idea.
when removing a lot of small files (make clean ?), it can freeze a computer for 5-10min.
it's the case on my laptop (quad-core with 6G RAM), and a better method is to add fstrim to a crontab.
when I say freeze, I mean all keystroke/click are delayed by 30-40s, so it's completely unusable.