Re: unclean shutdown and space cache rebuild

[Shridhar Daithankar <ghodechhap@ghodechhap.net>]

On Tuesday, July 02, 2013 01:00:29 PM Duncan wrote:
> Just to be clear, your system, your call.  I'd never /dream/ of
> interfering with that due to the implications for my own system (which is
> certainly highly customized even matched against a peer-group of other
> gentoo installs =:^).  That said...
> 
> I'm guessing what you experiences with the autodefrag mount option was
> because you were not in stable-state yet.  The original btrfs filesystem
> setup and fill was very likely without the flag on[2], so there's quite a
> lot of existing fragmentation what would have to be worked thru before
> the filesystem gets defragged and you reach stable-state, at which I'd
> expect the autodefrag mount option to have little overhead.

Yes, I suspect as much. One of the data parition I have is over an year old 
and never defragged, /home about 3 months old.

and I can see the defragmentation working when run by hand. The initial run on 
/var(only directories, to defrag metadata) was 6 min. Now that I am running it 
daily by hand, entire /var(including files, that includes 1.8G pacman cache, 
few tiny postgresql databases and /var/tmp where kde generates tons of IO) 
takes about 6-7 min.

Despite of my experience with autodefrag, I want to use it because thats the 
best solution(kinda like autovacuum in postgresql) that keeps things clean, 
all the time.

> 
> Tho if what you're saying is correct[1] then it may be that the
> background defrag thread isn't (io-)niced as I would have expected it to
> be.
> 
> But I'd still expect there to be some better performance steady state
> after a few mounts gets the basic filesystem defragged.  Tho if the
> fileystem is heavily fragmented[2], in practice it may well be easier to
> backup the filesystem content, do a clean mkfs and mount with autodefrag
> and restore from backup, thus ensuring autodefrag is on while filling the
> filesystem in the first place, than to wait for autodefrag to reach a
> stable system state in normal operation over many mounts.

well, I think I will bite the bullet and defrag entire / overnight and repeat 
the autodefrag mount option. That should work too.

Thanks

-- 
Regards
 Shridhar