Re: btrfs filesystem keeps allocating new chunks for no apparent reason

[Kai Krakow <hurikhan77@gmail.com>]

Am Mon, 10 Apr 2017 18:44:44 +0200
schrieb Kai Krakow <hurikhan77@gmail.com>:

> Am Mon, 10 Apr 2017 08:51:38 -0400
> schrieb "Austin S. Hemmelgarn" <ahferroin7@gmail.com>:
> 
> > On 2017-04-10 08:45, Kai Krakow wrote:  
> > > Am Mon, 10 Apr 2017 08:39:23 -0400
> > > schrieb "Austin S. Hemmelgarn" <ahferroin7@gmail.com>:
> > >    
>  [...]  
> > >
> > > Does btrfs really support lazytime now?
> > >    
> > It appears to, I do see fewer writes with it than without it.  At
> > the very least, if it doesn't, then nothing complains about it.  
> 
> Did you put it in /etc/fstab only for the rootfs? If yes, it probably
> has no effect. You would need to give it as rootflags on the kernel
> cmdline.

I did a "fgrep lazytime /usr/src/linux -ir" and it reveals only ext4
and f2fs know the flag. Kernel 4.10.

So probably you're seeing a placebo effect. If you put lazytime for
rootfs just only into fstab, it won't have an effect because on initial
mount this file cannot be opened (for obvious reasons), and on remount,
btrfs seems to happily accept lazytime but it has no effect. It won't
show up in /proc/mounts. Try using it in rootflags kernel cmdline and
you should see that the kernel won't accept the flag lazytime.

-- 
Regards,
Kai

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