I've been using btrfs on the raspi3 with archlinux arm for some time now and it seems that there is something wrong with the quotas and qgroups. I've used snapper and buttersink which both use quotas and also creates them. The filesystem is on an sd card, so I cannot guarantee that that did not cause the issue, but I think it did not.

The filesystem itself seems to work fine except a few parts:
I cannot create a new quota limit with snapper for my home setting. The operation times out. The btrfs check reports errors about the qgroups and if I list them on the operating device itself they are mostly incorrect.

I am not sure which program caused the issue or if its a kernel bug. However my filesystem seems half broken and I want to find out why and how to fix it. If there is another place where I should report this, let me know.

The output below was made with archlinux x64 and btrfs-progs 4.8.1
The raspi (with the btrfs) runs a 4.4 kernel.

$ sudo btrfs check --repair /dev/mapper/raspi
enabling repair mode
Checking filesystem on /dev/mapper/raspi
UUID: fdadc198-542b-4833-9ec9-e9911fa63f22
Fixed 0 roots.
checking free space cache
checking extentscache and super generation don't match, space cache will be invalidated
checking fs roots
checking csums
checking root refs
checking quota groups
ERROR: out of memory
ERROR: Loading qgroups from disk: -2
found 5791219712 bytes used err is 0
total csum bytes: 4858920
total tree bytes: 537247744
total fs tree bytes: 514981888
total extent tree bytes: 15646720
btree space waste bytes: 93926039
file data blocks allocated: 16553922560
 referenced 14326509568
extent buffer leak: start 1027915776 len 16384
extent buffer leak: start 1033617408 len 16384