Re: commit 762380a "block: add notion of a chunk size for request merging" stops io on btrfs

[Jens Axboe <axboe@fb.com>]

On 2014-06-18 00:21, Konstantinos Skarlatos wrote:
> On 18/6/2014 5:11 πμ, Jens Axboe wrote:
>> On 2014-06-17 14:35, Konstantinos Skarlatos wrote:
>>> Hi all,
>>> with 3.16-rc1  rsync stops writing to my btrfs filesystem and stays at a
>>> D+ state.
>>> git bisect showed that the problematic commit is:
>>>
>>> 762380ad9322951cea4ce9d24864265f9c66a916 is the first bad commit
>>> commit 762380ad9322951cea4ce9d24864265f9c66a916
>>> Author: Jens Axboe <axboe@fb.com>
>>> Date:   Thu Jun 5 13:38:39 2014 -0600
>>>
>>>      block: add notion of a chunk size for request merging
>>>
>>>      Some drivers have different limits on what size a request should
>>>      optimally be, depending on the offset of the request. Similar to
>>>      dividing a device into chunks. Add a setting that allows the driver
>>>      to inform the block layer of such a chunk size. The block layer
>>> will
>>>      then prevent merging across the chunks.
>>>
>>>      This is needed to optimally support NVMe with a non-zero stripe
>>> size.
>>>
>>>      Signed-off-by: Jens Axboe <axboe@fb.com>
>>
>> That's odd, should not have any effect since nobody enables stripe
>> sizes in the kernel. I'll double check, perhaps it's not always being
>> cleared.
>>
>> Ah wait, does the attached help?
>
> Yes, it works! I recompiled at commit
> 762380ad9322951cea4ce9d24864265f9c66a916 with your patch and it looks
> ok. Rebooted back to the unpatched kernel and the bug showed up again
> immediately.
>
> The funny thing is that the problem only showed on my (multi-disk) btrfs
> filesystem. / which is on ext4 seems to work fine.

Probably because the multi-disk setup doesn't have hw_sectors set, I'm 
guessing. But great, I'll get this upstream asap. Thanks for testing!

-- 
Jens Axboe