Re: ERROR... please contact btrfs developers

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

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On 2020/10/5 下午5:05, Eric Levy wrote:
> The volume is not RAID, only a single NVMe card.

Then this means, we may have a bigger problem.

Normally btrfs space reservation keeps enough margin for critical
operations, thus it will return ENOSPC before we really go to do some
space consuming operations, thus no abort_transaction problem like yours.

If it's single device, and still hit the case we need more space than we
have, either the space reservation or the space consumer,
btrfs_drop_snapshot(), has something wrong.
> 
> I deleted all the files and subvolumes except what I need to recover.

You may want to wait until btrfs really drops the subvolume/snapshot.

The command is "btrfs subv sync <mount>". And then check if the usage drops.

> 
> Below is the dump from fi usage. It looks as though 1.00Mb is all that
> is unallocated.
> 
> 
> $ sudo btrfs fi usage /mnt/custom
> Overall:
>     Device size:         378.04GiB
>     Device allocated:         378.04GiB
>     Device unallocated:           1.00MiB
>     Device missing:             0.00B
>     Used:             323.54GiB
>     Free (estimated):          53.13GiB    (min: 53.13GiB)
>     Data ratio:                  1.00
>     Metadata ratio:              1.00
>     Global reserve:         512.00MiB    (used: 0.00B)
> 
> Data,single: Size:371.02GiB, Used:317.89GiB (85.68%)
>    /dev/sdb5     371.02GiB
> 
> Metadata,single: Size:7.01GiB, Used:5.65GiB (80.66%)
>    /dev/sdb5       7.01GiB

This is strange. Even accounting the GlobalRSV (0.5G), we should still
have 1GiB space for metadata.
We shouldn't use that much space just for delete.

Would you please try a more uptodate kernel to see if it works?
(One simpler solution is using rolling release ISOs, like OpenSUSE
tumbleweed or Arch install iso).

I'm wondering it may be a bug not fixed in v4.15 due to the hardness to
backport.


BTW, when mounting the fs, you may want to mount with skip_balance mount
option.

Thanks,
Qu

> 
> System,single: Size:4.00MiB, Used:64.00KiB (1.56%)
>    /dev/sdb5       4.00MiB
> 
> Unallocated:
>    /dev/sdb5       1.00MiB
> 
> 
>> Oh, that's a completely different bug.
>>
>> Somehow btrfs exhausted the metadata space.
>>
>> Normally caused by unbalanced data/metadata usage and multi-device.
>> (Currently, RAID1/RAID0/RAID10/RAID5/RAID6 can all over-estimate the
>> available space, and cause ENOSPC to happen in critical context, where
>> we can only abort transaction to avoid further corruption)
>>
>> Currently I guess you need to don't do any balance, but try to remove as
>> many unused files as possible, until you have enough unallocated space
>> for metadata.
>>
>> To check your unalloated space, you can use btrfs fi usage:


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