At 06/01/2016 08:50 AM, Mark Fasheh wrote:
On Mon, May 30, 2016 at 03:48:14PM +0800, Qu Wenruo wrote:
Mark Fasheh wrote on 2016/05/26 17:18 -0700:
The btrfs balance operation is significantly slower when qgroups are
enabled. To the best of my knowledge, a balance shouldn't have an effect on
qgroups counts (extents are not changing between subvolumes), so we don't
need to actually run the qgroup code when we balance.
This assumption is questionable.
When balancing, it's true we will set the chunk to ro, so new
*allocation* won't happen in that chunk.
However we can still de-refer an extent during balance.
If that happens and we skipped the qgroup accounting, corruption happens.
As the extent before and after balance won't go through qgroup, so
it's de-reference won't be accounted.
Ok, thanks for the review. I was afraid that this was the case.
While without your patch, the final qgroup is stable with 16KiB.
Qgroups in general are broken with respect to balance. The following script
reproduces an inconsistency every time I run it. You'll notice that qgroups
aren't even turned on until before we do the balance op. Like the snap
create bug, I believe you simply need a non-trivial amount of data on the fs
for testing.
#!/bin/bash -x
MNT="/btrfs"
DEV="/dev/vdb1"
mkfs.btrfs -f $DEV
mount -t btrfs $DEV $MNT
mkdir $MNT/snaps
echo "populate $MNT with some data"
#cp -a /usr/share/fonts $MNT/
cp -a /usr/ $MNT/ &
for i in `seq -w 0 8`; do
S="$MNT/snaps/snap$i"
echo "create and populate $S"
btrfs su snap $MNT $S;
cp -a /boot $S;
done;
#let the cp from above finish
wait
btrfs fi sync $MNT
btrfs quota enable $MNT
btrfs quota rescan -w $MNT
btrfs qg show $MNT
umount $MNT
mount -t btrfs $DEV $MNT
time btrfs balance start --full-balance $MNT
umount $MNT
btrfsck $DEV
Thanks　for the test case.
It would be better if you could submit a test case for it.
Reproduced the problem. I'll track it down.
Seems to be related with metadata.
Thanks,
Qu
The xfstest case will follow soon.
Ok, that will help the next time someone tries to fix this, thanks.
--Mark
--
Mark Fasheh
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