fix for slow unmount on ext4 - bug 543617 on lp

[Stefan Bader]

On 06/09/2010 09:06 PM, Kees Cook wrote:
> Hi Stefan,
> 
> On Mon, Jun 07, 2010 at 02:10:43PM +0200, Stefan Bader wrote:
>> Ok, so upstream seems to have officially reverted the changes for now. Given
>> that the changes in that area seem to have unexpected side effects and we do not
>> really know the other patch would not do the same. When reverting the
>> work-around we got huge sync times. IIRC the side effects of that patch were not
>> as bad timewise (2 seconds?). So maybe for now, we stay with what we got and
>> wait for the proper upstream solution?
> 
> Upstream gave up on fixing the problem?  Argh.
> 

No not given up but currently needing to come up with a better solution.

> Huge sync times in Lucid?  When what was changed?
> 

Err, wasn't that the reason for the patch below in the first place? Maybe my
description was not completely accurate. It was very long time to unmount. I
might be wrong but in my memory that was as bad as 30m in bad cases.
For which the reason is that sync is done syncronously.

> I think we need to revert 5e1941884c700b7b97bcad52c2d8212ac56a7ebc even
> if there isn't a good fix for the umount slow-down since it solves the
> slow umount only under certain conditions, and makes other more common
> umount scenarios slower.
> 

The question would be how much slower. If it is possible to live with the
current status a little longer, then I'd rather wait for the correct upstream
fix, than to revert this patch to see one regression fixed by another one coming
back.

Stefan

> -Kees
>