Re: Btrfs autodefrag wrote 5TB in one day to a 0.5TB SSD without a measurable benefit

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

On 2022/3/10 12:33, Jan Ziak wrote:
> On Thu, Mar 10, 2022 at 2:26 AM Qu Wenruo <quwenruo.btrfs@gmx.com> wrote:
>> ## Enable trace
>>
>> echo 1 > $tracedir/tracing_on
>>
>> ## After the consistent write happens, just copy the trace file
>>
>> cp /sys/kernel/debug/tracing/trace /tmp/whatevername
>
> The compressed trace is attached to this email. Inode 307273 is the
> 40GB sqlite file, it currently has 1689020 extents. This time, it took
> about 3 hours after "mount / -o remount,autodefrag" for the issue to
> start manifesting itself.

Sorry, considering your sqlite file is so large, there are too many
defrag_one_locked_range() and defrag_add_target() calls.

And the buffer size is a little too small.

Mind to re-take the trace with the following commands?
(No need to reboot, it takes effect immediate)

cd /sys/kernel/debug/tracing
echo 0 > tracing_on
echo > trace
echo > set_event
echo 65536 > buffer_size_kb
echo "btrfs:defrag_file_start" >> set_event
echo "btrfs:defrag_file_end" >> set_event
echo 1 > $tracedir/tracing_on

## After the consistent write happens, just copy the trace file

cp /sys/kernel/debug/tracing/trace /tmp/whatevername

Thanks,
Qu
>
> -Jan