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

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

On 2022/10/9 19:13, Qu Wenruo wrote:
>
>
> 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...

My bad, two versions too old.

>
> In fact, v5.0 kernel we have introduced a lot of qgroup optimization to

Git describes --contains shows it's v5.1 for the optimization.

> 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
>>