Re: [RFC 0/1] adapting btrfs/237 to work with the new reclaim algorithm

[Pankaj Raghav <p.raghav@samsung.com>]

On 2022-08-22 16:29, Johannes Thumshirn wrote:
>>
>> Only partial reclaim is happening for bigger sized drives. The issue
>> with that is, if I do another FIO transfer, the drive spits out ENOSPC
>> before its actual capacity is reached as most of the zones have not been
>> reclaimed back and are basically in an unusable state.
>>
>> Is there a limit on how many bgs can be reclaimed?
>>
>> Let me know if I am doing something wrong in the test or if it is an
>> actual issue.
> 
> Can you try setting max_active_zones to 0? I have the feeling it's yet 
> another (or perhaps already known, Naohiro shoudl know that) issue with 
> MAZ handling.

The Max active zones is set to 0 (QEMU defaults to 0). I also changed the
backing image format of QEMU from qcow to raw, and still the same issue of
partial reclaim for a drive size of 100G.

I tried the same test in a 100G drive with 1G zone size, and it is working
as expected.

root@zns-btrfs-simple-zns:/data# ./reclaim_script.sh
Open zones before big file transfer:
4
Open zones before removing the file:
59
Going to sleep. Removed the file
Open zones after reclaim:
4

I am not 100% sure what is causing this issue of partial reclaim when the
number of zones is higher.