My system has been going sluggish lately. After getting suspicious, I decided to check if TRIM was working.
How to check and enable
$ sudo dmsetup table … luks-123abcdef-etc: 0 1234567 crypt aes-xts-plain64 000etc000 0 8:2 4096 1 allow_discards …
If you see
allow_discards on every relevant entry (like above), you’re all
set. If not, run
$ rpm-ostree kargs --append=rd.luks.options=discard
This applies the ‘discards’ flag at boot time, enabling it for all partitions
on the root drive. (If you only want this for some, use
rd.luks.options=<LUKS partition ID>=discard). Restart and run
fstrim.service. On my machine, it was a difference between light and day.