Re: Applications using fsync cause hangs for several seconds every few minutes

[Andrew Guertin <andrew.guertin@uvm.edu>]

On 08/09/2011 05:29 PM, Andrew Guertin wrote:
> On 06/21/2011 01:15 PM, Jan Stilow wrote:
>> Hello,
>>
>> Nirbheek Chauhan <nirbheek <at> gentoo.org> writes:
>>> [...]
>>>
>>> Every few minutes, (I guess) when applications do fsync (firefox,
>>> xchat, vim, etc), all applications that use fsync() hang for several
>>> seconds, and applications that use general IO suffer extreme
>>> slowdowns. iotop shows various combinations of the processes listed
>>> below doing writes, and the total write as 2-3MB/s.
>>>
>>> [btrfs-dealloc-]
>>> [btrfs-submit-0]
>>> [btrfs-transacti]
>>> [btrfs-endio-wri]
>>> [flush-btrfs-1]
>>
>> I'm using btrfs under a 2.6.39-ARCH kernel and run into the same issue.
>>
>> In my case the [btrfs-submit-0] and [btrfs-transacti] shows up in iotop
>> and produce 99% of IO at the time a application is frozen. For something
>> like 10 to 30 seconds.
>>
>> [...]
> 
> I see the same issue. I have bisected it to
> 
> 4e69b598f6cfb0940b75abf7e179d6020e94ad1e is the first bad commit
> commit 4e69b598f6cfb0940b75abf7e179d6020e94ad1e
> Author: Josef Bacik <josef@redhat.com>
> Date:   Mon Mar 21 10:11:24 2011 -0400
> 
> Btrfs: cleanup how we setup free space clusters
> 
> ...which came in between 2.6.38 and 2.6.39.

Any chance of someone looking at this? I (and presumably others) haven't
been able to upgrade my kernel past 2.6.38 because of this.

--Andrew