On Wed, Jul 04, 2012 at 07:40:05AM +0700, Fajar A. Nugraha wrote:
> Are there any known btrfs regression in 3.4? I'm using 3.4.0-3-generic
> from a ppa, but a normal mount - umount cycle seems MUCH longer
> compared to how it was on 3.2, and iostat shows the disk is
> read-IOPS-bound

Is it just mount/umount without any other activity? Is the fs
fragmented (or aged), almost full, has lots of files?

> 
> # time mount LABEL=WD-root
> 
> real  0m10.400s
> user  0m0.000s
> sys   0m0.060s
> 
> # time umount /media/WD-root/
> 
> real  0m22.419s
> user  0m0.000s
> sys   0m0.064s
> 
> # /proc/10142/stack  <--- the PID of umount process

The process(es) actually doing the work are the btrfs workers, usual
sucspects are btrfs-cache (free space cache) or btrfs-ino (inode cache)
that are writing the cache states back to disk.
I'm using iotop to observe such things.


david
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