Re: spinning kworker with space_cache=v2 searching for free space

[Stefan Priebe - Profihost AG <s.priebe@profihost.ag>]

Am 12.11.2016 um 03:18 schrieb Liu Bo:
> On Wed, Nov 09, 2016 at 09:19:21PM +0100, Stefan Priebe - Profihost AG wrote:
>> Hello,
>>
>> found this one from 2014:
>> https://patchwork.kernel.org/patch/5551651/
>>
>> it this still valid?
> 
> The space cache code doesn't change a lot, so I think the patch is still
> valid to apply(there might be some conflicts though), but I'm not sure
> if it could help the spinning case.

Thanks got it applied and will try it. Any other ideas why it's pinning
there? Free space fragmentation?

But at least on one machine there are 26TB free and it's spinning...
slowing down the performance.

Greets,
Stefan

> 
> Thanks,
> 
> -liubo
>>
>> Am 09.11.2016 um 09:09 schrieb Stefan Priebe - Profihost AG:
>>> Dear list,
>>>
>>> even there's a lot of free space on my disk:
>>>
>>> # df -h /vmbackup/
>>> Filesystem                    Size  Used Avail Use% Mounted on
>>> /dev/mapper/stripe0-backup   37T   24T   13T  64% /backup
>>>
>>> # btrfs filesystem df /backup/
>>> Data, single: total=23.75TiB, used=22.83TiB
>>> System, DUP: total=8.00MiB, used=3.94MiB
>>> Metadata, DUP: total=283.50GiB, used=105.82GiB
>>> GlobalReserve, single: total=512.00MiB, used=0.00B
>>>
>>> I always have a kworker process endless spinning.
>>>
>>> # perf top shows:
>>>   47,56%  [kernel]               [k] rb_next
>>>    7,71%  [kernel]               [k] tree_search_offset.isra.25
>>>    6,44%  [kernel]               [k] btrfs_find_space_for_alloc
>>>
>>> Mount options:
>>> rw,noatime,compress-force=zlib,nossd,noacl,space_cache=v2,skip_balance
>>>
>>> What's wrong here?
>>>
>>> Greets,
>>> Stefan
>>>