> Also, since you don't have any snapshots, you could also find this
> conventionally:
>
> # du -sh /*
Usually yes, but here not. It's just like when you remove a file when
a process still use it and write in it, and fcsk will be not happy
next time.
But I reboot & check with btrfs check withtout any issue :-/
alian@alian:/> sudo btrfs fi du -s *
Total Exclusive Set shared Filename
1.58MiB 1.58MiB 0.00B bin
42.69MiB 42.69MiB 0.00B boot
14.78MiB 14.78MiB 0.00B etc
532.40MiB 532.40MiB 0.00B lib
9.88MiB 9.88MiB 0.00B lib64
0.00B 0.00B 0.00B mnt
23.96MiB 23.96MiB 0.00B opt
128.00KiB 128.00KiB 0.00B root
9.74MiB 9.74MiB 0.00B sbin
0.00B 0.00B 0.00B selinux
0.00B 0.00B 0.00B srv
15.92MiB 15.92MiB 0.00B tmp
4.86GiB 4.86GiB 0.00B usr
345.65MiB 345.65MiB 0.00B var
alian@alian:~> sudo du --exclude /home -sh /*
2,1M /bin
43M /boot
0 /dev
20M /etc
534M /lib
11M /lib64
0 /mnt
24M /opt
0 /proc
172K /root
18M /run
11M /sbin
0 /selinux
0 /srv
0 /sys
16M /tmp
5,2G /usr
355M /var
