Btrfs missing space

- Reclaiming some lost btrfs space

solo_02:~ # btrfs fi df / 
Data, single: total=6.00GiB, used=5.97GiB
System, DUP: total=32.00MiB, used=16.00KiB
Metadata, DUP: total=512.00MiB, used=215.73MiB
GlobalReserve, single: total=19.08MiB, used=0.00B
solo_02:~ # df -h
Filesystem Size Used Avail Use% Mounted on
devtmpfs 988M 0 988M 0% /dev
tmpfs 996M 55M 941M 6% /dev/shm
tmpfs 996M 8,9M 987M 1% /run
tmpfs 996M 0 996M 0% /sys/fs/cgroup
/dev/sda2 11G 6,5G 3,3G 67% /
/dev/sda2 11G 6,5G 3,3G 67% /.snapshots
/dev/sda2 11G 6,5G 3,3G 67% /tmp
/dev/sda2 11G 6,5G 3,3G 67% /boot/grub2/x86_64-efi
/dev/sda2 11G 6,5G 3,3G 67% /opt
/dev/sda2 11G 6,5G 3,3G 67% /srv
/dev/sda2 11G 6,5G 3,3G 67% /usr/local
/dev/sda2 11G 6,5G 3,3G 67% /var
/dev/sda2 11G 6,5G 3,3G 67% /root
/dev/sda2 11G 6,5G 3,3G 67% /boot/grub2/i386-pc
/dev/sda4 7,2G 40M 7,2G 1% /home
tmpfs 200M 0 200M 0% /run/user/0
solo_02:~ # snapper list
# | Type | Pre # | Date | User | Used Space | Cleanup | Description | Userdata
---+--------+-------+-------------------------------+------+------------+---------+-----------------------+--------------
0 | single | | | root | | | current |
1* | single | | dom 14 out 2018 20:34:07 WEST | root | 1,38 GiB | | first root filesystem |
2 | single | | dom 14 out 2018 20:57:18 WEST | root | 893,95 MiB | number | after installation | important=yes

solo_02:~ # btrfs sub list /
ID 256 gen 61539 top level 5 path @
ID 258 gen 61658 top level 256 path @/var
ID 259 gen 61539 top level 256 path @/usr/local
ID 260 gen 61656 top level 256 path @/tmp
ID 261 gen 61539 top level 256 path @/srv
ID 262 gen 61653 top level 256 path @/root
ID 263 gen 61539 top level 256 path @/opt
ID 264 gen 61539 top level 256 path @/boot/grub2/x86_64-efi
ID 265 gen 61557 top level 256 path @/boot/grub2/i386-pc
ID 266 gen 61539 top level 256 path @/.snapshots
ID 267 gen 61658 top level 266 path @/.snapshots/1/snapshot
ID 270 gen 61566 top level 266 path @/.snapshots/2/snapshot
ID 311 gen 61566 top level 266 path @/.snapshots/4/snapshot

solo_02:~ # btrfs sub delete /.snapshots/4/snapshot
Delete subvolume (no-commit): '/.snapshots/4/snapshot'
solo_02:~ # btrfs sub list / 
ID 256 gen 61539 top level 5 path @
ID 258 gen 61663 top level 256 path @/var
ID 259 gen 61539 top level 256 path @/usr/local
ID 260 gen 61656 top level 256 path @/tmp
ID 261 gen 61539 top level 256 path @/srv
ID 262 gen 61659 top level 256 path @/root
ID 263 gen 61539 top level 256 path @/opt
ID 264 gen 61539 top level 256 path @/boot/grub2/x86_64-efi
ID 265 gen 61557 top level 256 path @/boot/grub2/i386-pc
ID 266 gen 61664 top level 256 path @/.snapshots
ID 267 gen 61664 top level 266 path @/.snapshots/1/snapshot
ID 270 gen 61566 top level 266 path @/.snapshots/2/snapshot
solo_02:~ # df -h
Filesystem      Size  Used Avail Use% Mounted on
devtmpfs        988M     0  988M   0% /dev
tmpfs           996M   55M  941M   6% /dev/shm
tmpfs           996M  8,9M  987M   1% /run
tmpfs           996M     0  996M   0% /sys/fs/cgroup
/dev/sda2        11G  4,6G  5,1G  48% /
/dev/sda2        11G  4,6G  5,1G  48% /.snapshots
/dev/sda2        11G  4,6G  5,1G  48% /tmp
/dev/sda2        11G  4,6G  5,1G  48% /boot/grub2/x86_64-efi
/dev/sda2        11G  4,6G  5,1G  48% /opt
/dev/sda2        11G  4,6G  5,1G  48% /srv
/dev/sda2        11G  4,6G  5,1G  48% /usr/local
/dev/sda2        11G  4,6G  5,1G  48% /var
/dev/sda2        11G  4,6G  5,1G  48% /root
/dev/sda2        11G  4,6G  5,1G  48% /boot/grub2/i386-pc
/dev/sda4       7,2G   40M  7,2G   1% /home
tmpfs           200M     0  200M   0% /run/user/0