Re: btrfs thinks fs is full, though 11GB should be still free

[Goffredo Baroncelli <kreijack@inwind.it>]

On 21/12/2023 14.53, Christoph Anton Mitterer wrote:
> Hey Goffredo.
> 
> On Tue, 2023-12-19 at 20:09 +0100, Goffredo Baroncelli wrote:
>> Ok, now we have the case study.
>> To be sure, could you try a defrag (+ sync) of this single file ?
> 
> # btrfs filesystem defragment /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> # btrfs filesystem defragment -t 1000M /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> # sync
> # btrfs filesystem sync /data/main/
> # compsize /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> Processed 1 file, 1 regular extents (1 refs), 0 inline.
> Type       Perc     Disk Usage   Uncompressed Referenced
> TOTAL      100%      256M         256M          15M
> none       100%      256M         256M          15M
> #
> 
> 
> 
>> The what is the lsof output ?
> 
> # lsof -- /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> COMMAND       PID       USER   FD   TYPE DEVICE SIZE/OFF NODE NAME
> prometheu 2327412 prometheus   12r   REG   0,43 15781418  642 /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> #
> 
> I also stopped prometheus synced and checked then:
> # systemctl stop prometheus.service
> # lsof -- /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001

Here you should do a defrag, after the stop of prometheus.

> # btrfs filesystem sync /data/main/
> # compsize /data/main/prometheus/metrics2/01HHFEZPJ8TPFVYTXV11R7ZH4X/chunks/000001
> Processed 1 file, 1 regular extents (1 refs), 0 inline.
> Type       Perc     Disk Usage   Uncompressed Referenced
> TOTAL      100%      256M         256M          15M
> none       100%      256M         256M          15M
> 
> 
>> Does anyone know a way to extract the "owners" of an extent ? I think
>> that
>> we should go through the backref, but I never did. I don't want to
>> re-invent the wheel, so I am asking if someone knows a tool that can
>> help to find the owners of a extent.
> 
> Not me ;-) ... Does it help if I'd provide something like dump-tree
> data?
> 
I am trying to write a tool that walks the backref to find the owners.
I hope for tomorrow to have a prototype to test.

> 
> The fs is soon to be full again, so I'll likely have to delete some of
> the (test) data...
> 
> 
> Thanks,
> Chris.

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