Re: freezes during snapshot creation/deletion -- to be expected? (Was: Re: btrfs based backup?)

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On 2019/11/22 下午8:30, Christian Pernegger wrote:
> Am Fr., 22. Nov. 2019 um 00:57 Uhr schrieb Oliver Freyermuth
> <o.freyermuth@xxxxxxxxxxxxxx>:
>>> 2) I'm wondering if this couldn't be improved. [...]
>>
>> You can check e.g. the man page btrfs-quota(8) for a short discussion on why doing quota correctly
>> with btrfs is not as easy as it may seem.
> 
> I've read that and I appreciate the difficulties in getting accurate
> usage information (or even defining what that means) from a COW
> filesystem. IMHO, performance, and the trade-off between performance
> and up-to-the-minute accuracy are separate issues.
> 
> FWIW, running btrfs quota disable, enable, and rescan got rid of the
> orphan qgroups. The full rescan ran for all of 3 seconds and didn't
> block.

BTW, for the empty qgroup auto delete, we have pending patch for that
already.
Just not merged yet.

https://patchwork.kernel.org/patch/11195067/


But still, for snapshot deletion part, there is still a performance impact.
(For completely independent subvolume, IIRC there is a quick path for
it, thus no performance penalty then)

Thanks,
Qu
> 
> Cheers,
> C.
> 

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