Re: BTRFS w/ quotas hangs on read-write mount using all available RAM - rev2

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

On 2022/10/9 19:03, admiral@admiralbulli.de wrote:
> Dear btrfs team,
> thanks for all your great work!
> I have been running btrfs now for several years and really like the
> robustness and ease of use!
>
> Last week I experienced 99% the same thing as described here by Loren M.
> Lang:
> https://www.spinics.net/lists/linux-btrfs/msg81173.html
> only difference: This is not my / but a 40TB storage mounted to
> /media/btrfs1/
>
> quick summary what happend:
> - enabled quotas to better understand where all my space has gone
> - started balancing
> - system got completely stuck due to the meanwhile well understood reasons
> - pushed reset button
>
> I can mount my btrfs system perfectly read-only and access the data. As soon
> as I try to mount rw, my system will exremely slow down, memory will fill up
> until I will finally end up with a panicking kernel.
>
> So, no problem to successfully boot with the fstab entries on ro or
> commented out.
>
>     admiral@server:/$ uname -a
>     Linux server.domain.loc 4.19.0-21-amd64 #1 SMP Debian 4.19.249-2
> (2022-06-30) x86_64 GNU/Linux

Your kernel is just one version too old...

In fact, v5.0 kernel we have introduced a lot of qgroup optimization to
address the slow performance (including hang, huge memory usage) of
balance with qgroup enabled.

Although that optimization also introduced some regression, all the
known regression should have been fixed and backported.

But for older kernels, like your 4.x kernels, we don't have the
optimization at all.

Thus in your case, you may want to use the latest LTS kernel at least
(v5.15.x).

Thanks,
Qu

>
>     admiral@server:/$ btrfs --version
>     btrfs-progs v5.10.1
>
> Here the question:
> I am looking for the option to disable quota on an unmounted btrfs like
> described here:
> https://patchwork.kernel.org/project/linux-btrfs/patch/20180812013358.16431-
> 1-wqu@suse.com/
>
> All my trials and checks et cetera were performed with btrfs-progs v4.20.1-2
> as debian buster's latest state:
> https://packages.debian.org/de/buster/btrfs-progs
>
> I already upgraded the btrfs-progs to debian backport v5.10.1 but do not
> find any option to offline disable quota, yet:
> https://packages.debian.org/buster-backports/btrfs-progs
>
> Can you point me some direction how to move forward to recover the btrfs?
>
> Thanks a lot,
>
> admiralbulli
>