[PATCH 00/16]: Fix writeback regressions in 2.6.32

Stefan Bader stefan.bader at canonical.com
Tue Aug 10 09:49:36 UTC 2010


On 08/10/2010 11:38 AM, Stefan Bader wrote:
> On 08/10/2010 11:28 AM, Stefan Bader wrote:
>> Impact: 2.6.32 is facing some serious performance regression which are visible
>> plainly when unmounting filesystems as async writeback degrades to sync in
>> that case. But there seem to be other less visible problems as well.
>> I believe this set of patches also would be benefitial to go into upstream
>> stable.
>>
>> Fix: This series of patches was picked and backported when needed to apply
>> to 2.6.32.y (there is another set for 2.6.34.y[1]). It probably does not
>> solve all currently known problems but testing has shown considerable
>> improvements. At the beginning of the set there are some patches that were
>> picked to make the later patches applicable. Only one of them is a bit more
>> intrusive the others rather trivial.
>>
>> Testcase: Unmounting a fs that still has larger amounts of data to write back
>> to disk will take noticably longer time to complete (IIRC might be 30min).
>> Also general responsiveness was reported to improve. Currently there are no
>> known regressions reported when testing this backport.
>>
>> [1] git://kernel.ubuntu.com/smb/linux-2.6.34.y writeback
>>
> 
> This went upstream as well so it was actually missing one bit. We need to revert
> the following commit in our tree to get rid of a work-around only we were carrying.
> 
>     Revert "UBUNTU: SAUCE: sync before umount to reduce time taken by ext4 umoun
> 
>     This reverts commit 5e1941884c700b7b97bcad52c2d8212ac56a7ebc which was a
>     work around for the long sync on unmount problem but also caused other
>     regressions.
> 
> -Stefan
> 

One more addition: while the patch series was attributed to one LP bug, there is
another one open on this issue.

https://bugs.launchpad.net/ubuntu/+source/linux/+bug/543617

-Stefan




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