Re: space_cache=v2 on root fs

On 2016.01.18 at 19:27 +0100, Markus Trippelsdorf wrote:

Hi,

while testing the new space_cache=v2 mount option it looks like my root fs
doesn't automatically create the new space cache.

I'm using the following /etc/fstab:

UUID=7ef56edc-673e-452e-9e05-3fabf074168b       /               btrfs           noatime,compress=lzo,space_cache=v2             0 0
UUID=6b7d75bf-3d12-409c-88ed-500ac6b78510       /var            btrfs           compress=lzo,space_cache=v2                     0 0
UUID=24cee7e4-9093-4f86-aa73-d8a59d7f3c6c       /var/tmp        btrfs           compress=lzo,space_cache=v2                     0 0

During first mount the space cache was created for /var (/dev/sdb2) and
/var/tmp (/dev/sda3), but apparently not for / (/dev/sdc3):

Jan 18 18:48:18 x4 kernel: BTRFS info (device sdb2): enabling free space tree  
Jan 18 18:48:18 x4 kernel: BTRFS info (device sdb2): using free space tree 
Jan 18 18:48:18 x4 kernel: BTRFS: creating free space tree
Jan 18 18:48:18 x4 kernel: BTRFS info (device sdb2): setting 1 ro feature flag
Jan 18 18:48:18 x4 kernel: BTRFS: checking UUID tree
Jan 18 18:48:18 x4 kernel: BTRFS info (device sda3): enabling free space tree
Jan 18 18:48:18 x4 kernel: BTRFS info (device sda3): using free space tree
Jan 18 18:48:18 x4 kernel: BTRFS: has skinny extents
Jan 18 18:48:18 x4 kernel: BTRFS: detected SSD devices, enabling SSD mode
Jan 18 18:48:18 x4 kernel: BTRFS: creating free space tree
Jan 18 18:48:18 x4 kernel: BTRFS info (device sda3): setting 1 ro feature flag
Jan 18 18:48:18 x4 kernel: BTRFS: checking UUID tree
Jan 18 18:48:22 x4 kernel: BTRFS info (device sdc3): enabling free space tree
Jan 18 18:48:22 x4 kernel: BTRFS info (device sdc3): using free space tree

During subsequent boots the "enabling free space tree" message is
repeated every time for the root fs.

Jan 18 18:53:48 x4 kernel: BTRFS info (device sdb2): using free space tree 
Jan 18 18:53:48 x4 kernel: BTRFS info (device sda3): using free space tree 
Jan 18 18:53:52 x4 kernel: BTRFS info (device sdc3): enabling free space tree 
Jan 18 18:53:52 x4 kernel: BTRFS info (device sdc3): using free space tree  

To answer my own question. Adding "rw rootflags=space_cache=v2" to the
GRUB kernel entry fixes the issue...

-- 
Markus