Re: Suddenly cannot change metadata profile any longer (BISECTED)

["Holger Hoffstätte" <holger.hoffstaette@googlemail.com>]

On Sun, 15 Feb 2015 21:01:07 +0000, Holger Hoffstätte wrote:

> Here's a new one (with kernel 3.18.7++):
> 
> $btrfs --version
> Btrfs v3.18.2 (also tried 3.19-rc2)
> 
> $mount /dev/sdf1 /mnt/usb
> 
> $btrfs filesystem df /mnt/usb
> Data, single: total=8.00MiB, used=256.00KiB
> System, single: total=32.00MiB, used=16.00KiB
> Metadata, single: total=1.00GiB, used=112.00KiB
> GlobalReserve, single: total=16.00MiB, used=0.00B
> 
> Note: metadata=single - done right after mkfs for the initial balance.
> 
> $btrfs balance start -mconvert=dup /mnt/usb    
> Done, had to relocate 2 out of 3 chunks
> 
> root>btrfs filesystem df /mnt/usb              
> Data, single: total=8.00MiB, used=512.00KiB
> System, single: total=32.00MiB, used=16.00KiB
> Metadata, single: total=1.00GiB, used=192.00KiB
> GlobalReserve, single: total=16.00MiB, used=0.00B
> 
> Wait, what? Still single?
> 
> This used to work, but somehow no longer does (verified on another
> filesystem). If it's dup, it stays dup; if it's single, it stays single.
> 
> What works is the very first balance after the mkfs - it successfully
> changes from the initial default dup to single, but subsequent balances
> don't work. They also don't really fail.

Bisection found that commit 2f0810880f082fa8ba66ab2c33b02e4ff9770a5e [1]
in the integration tree is the cause:

  btrfs: delete chunk allocation attemp when setting block group ro

Reverting/omitting this patch lets me rebalance/convert at will.

thanks,
Holger

[1] https://git.kernel.org/cgit/linux/kernel/git/mason/linux-btrfs.git/commit/?h=integration&id=2f0810880f082fa8ba66ab2c33b02e4ff9770a5e