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

[Christoph Anton Mitterer <calestyo@scientia.org>]

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 
# 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?


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


Thanks,
Chris.