How to run SSD trim fstrim on btrfs when mounted multiple subvolumes?

Question

I am using btrfs and have mounted several subvolumes (but not btrfs root). It resides on SSD partition, so I would like to use fstrim. Should I call fstrim on each mountpoint (corresponding with different subvolume each) ? Or do I need to have btrfs root mounted and run fstrim on this mountpoint?

Answer 1

fstrim should run on "mountpoint", so you need to have devices mounted. But you only need to call it once per physical device. So if 2 mountpoints are on the same device with btrfs, you only need to call fstrim on one mountpoint.

Finding this answer: https://forums.gentoo.org/viewtopic-t-1003980-view-previous.html?sid=a51dab49787e5b7b6c2fa4aa7c1a5e44

I do it like this :

#!/bin/sh
LOG=/var/log/fstrim.log
echo "===" $(date -R) "===" >> $LOG
for d in $(lsblk -o MOUNTPOINT,FSTYPE | grep -E 'btrfs' | awk '{print $1}'); do
    fstrim -v $d 2>&1 >> $LOG
done

This script is placed in /etc/cron.weekly/fstrim and set executable:

sudo chmod +x /etc/cron.weekly/fstrim

The script makes use of lsblk that list block devices. I'm searching "btrfs" devices and I launch fstrim on it.