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

Stefan Bader stefan.bader at canonical.com
Tue Aug 10 09:38:38 UTC 2010


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




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