0d66f93ef3
fstrim timer triggers weekly to issue TRIM/DISCARD on devices that support it, which includes SD and MMC devices. This marks all unused diskspace as available for internal garbage collection and wear levelling on the card. It's preferrable to use the timer to the discard option, as it involves a one-off cost of latency over a global slowing down of all write or erase requests that the `discard` mount option does.