btrfs balance 4.0 regression?

btrfs balance 4.0 regression?

[Josh Boyer]

Hi Omar and Chris,

We have a bug reported [1] against 4.0 saying that btrfs balance is
broken.  The reporter found a revert patch that Omar sent [2] to
revert commit 2f0810880.  Looking in Linus' latest tree, I don't see
that revert and I don't immediately see a patch to fix the issue Omar
reported either.

Do either of you know if this is still an issue?  If not, which commit
was it fixed by?

josh

[1] https://bugzilla.redhat.com/show_bug.cgi?id=1217191
[2] https://patchwork.kernel.org/patch/6238111/

Re: btrfs balance 4.0 regression?

[Omar Sandoval]

On Fri, May 15, 2015 at 12:15:06AM +0000, Duncan wrote:
> Josh Boyer posted on Thu, 14 May 2015 08:43:25 -0400 as excerpted:
> 
> > Hi Omar and Chris,
> > 
> > We have a bug reported [1] against 4.0 saying that btrfs balance is
> > broken.  The reporter found a revert patch that Omar sent [2] to revert
> > commit 2f0810880.  Looking in Linus' latest tree, I don't see that
> > revert and I don't immediately see a patch to fix the issue Omar
> > reported either.
> > 
> > Do either of you know if this is still an issue?  If not, which commit
> > was it fixed by?
> > 
> > josh
> > 
> > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1217191
> > [2] https://patchwork.kernel.org/patch/6238111/
> 
> Still an issue, officially as of dev comments a day or two ago, at least.

Yup, Chris says he has a proper fix but it hasn't hit the list yet.

> From various comments including from Chris Mason directly, the devs are 
> aware of it, but (from a non-dev list-regular perspective) there's a 
> seeming reluctance to simply apply the revert patch.  Not being a dev I 
> can't explain why tho I can speculate that the patch is logically correct 
> and simply triggers this other bug.  But further patches have yet to 
> appear.
> 
> Part of the problem may be a bit of confusion as some of the devs 
> evidently thought the revert patch fixed the problem and hadn't been 
> worrying about it until others pointed out the revert hadn't been applied 
> and the problem thus remained.
> 
> So as of now, the choice appears to be broken balance-convert with the 
> current code, or broken ext*-convert with that patch reverted.  Both 
> cases aren't entirely common, so I guess it's up to you which you want to 
> break ATM.

Actually, ext4 convert is broken anyways (with irrelevant output
elided):

# mkfs.ext4 -F /dev/vdb
# btrfs-convert /dev/vdb
# mount /dev/vdb /mnt
# btrfs fi df /mnt
Data, single: total=2.64GiB, used=163.70MiB		<- single
System, single: total=32.00MiB, used=16.00KiB		<- single
Metadata, single: total=1.33GiB, used=37.13MiB		<- single
GlobalReserve, single: total=16.00MiB, used=0.00B	<- single
# btrfs device add -f /dev/vdc /mnt
# btrfs balance start -dconvert=raid1 -mconvert=raid1 /mnt
Done, had to relocate 9 out of 9 chunks
# btrfs fi df /mnt
Data, single: total=832.00MiB, used=200.55MiB		<- still single
System, single: total=32.00MiB, used=16.00KiB		<- still single
Metadata, single: total=256.00MiB, used=368.00KiB	<- still single
GlobalReserve, single: total=16.00MiB, used=0.00B	<- still single

So the balance succeeds unlike before the commit that caused the
regression, but the profile is still single, which defeats the purpose.

-- 
Omar

Re: btrfs balance 4.0 regression?

[Chris Murphy]

On Thu, May 14, 2015 at 6:33 PM, Omar Sandoval <osandov@osandov.com> wrote:
>
>
> Yup, Chris says he has a proper fix but it hasn't hit the list yet.
>
>
> Actually, ext4 convert is broken anyways (with irrelevant output
> elided):


I'm curious how this bug ended up in mainline. Isn't there an XFS test
for both balance+convert and ext4 convert? If not, shouldn't there be?
It's not a data loss bug but Btrfs is in a transitional stretch where
functionality loss bugs are no longer minor. (I'd look but I'm lazy
and xfs tests doesn't appear to be indexed.)


-- 
Chris Murphy

Re: btrfs balance 4.0 regression?

[Omar Sandoval]

On Thu, May 14, 2015 at 05:33:29PM -0700, Omar Sandoval wrote:
> On Fri, May 15, 2015 at 12:15:06AM +0000, Duncan wrote:
> > Josh Boyer posted on Thu, 14 May 2015 08:43:25 -0400 as excerpted:
> > 
> > > Hi Omar and Chris,
> > > 
> > > We have a bug reported [1] against 4.0 saying that btrfs balance is
> > > broken.  The reporter found a revert patch that Omar sent [2] to revert
> > > commit 2f0810880.  Looking in Linus' latest tree, I don't see that
> > > revert and I don't immediately see a patch to fix the issue Omar
> > > reported either.
> > > 
> > > Do either of you know if this is still an issue?  If not, which commit
> > > was it fixed by?
> > > 
> > > josh
> > > 
> > > [1] https://bugzilla.redhat.com/show_bug.cgi?id=1217191
> > > [2] https://patchwork.kernel.org/patch/6238111/
> > 
> > Still an issue, officially as of dev comments a day or two ago, at least.
> 
> Yup, Chris says he has a proper fix but it hasn't hit the list yet.
> 
> > From various comments including from Chris Mason directly, the devs are 
> > aware of it, but (from a non-dev list-regular perspective) there's a 
> > seeming reluctance to simply apply the revert patch.  Not being a dev I 
> > can't explain why tho I can speculate that the patch is logically correct 
> > and simply triggers this other bug.  But further patches have yet to 
> > appear.
> > 
> > Part of the problem may be a bit of confusion as some of the devs 
> > evidently thought the revert patch fixed the problem and hadn't been 
> > worrying about it until others pointed out the revert hadn't been applied 
> > and the problem thus remained.
> > 
> > So as of now, the choice appears to be broken balance-convert with the 
> > current code, or broken ext*-convert with that patch reverted.  Both 
> > cases aren't entirely common, so I guess it's up to you which you want to 
> > break ATM.
> 
> Actually, ext4 convert is broken anyways (with irrelevant output
> elided):

(I realize that I was being a bit too alarmist here. Reposting a message
from another thread clarifying.)

"""
Just to clarify, reverting 2f0810880f082fa8ba66ab2c33b02e4ff9770a5e does
not break ext4 conversion. If you revert it, you can btrfs-convert, do a
btrfs balance to finalize the conversion, then do another btrfs balance
-dconvert=... -mconvert=... to convert the profile. I should have been
clearer in that other thread: conversion from ext4 to Btrfs works, its
just that the commit that caused the regression did not actually
accomplish what it set out to do: allow converting the data/metadata
profile of a freshly btrfs-converted ext4 filesystem.
"""


-- 
Omar