Re: [PATCH] Btrfs: do not loop through raid types when looking for free extent

[Chris Mason <chris.mason@oracle.com>]

Excerpts from Yan, Zheng's message of 2010-12-13 20:54:12 -0500:
> On Tue, Dec 14, 2010 at 9:33 AM, Chris Mason <chris.mason@oracle.com>=
 wrote:
> > Excerpts from Yan, Zheng's message of 2010-11-16 20:38:23 -0500:
> >> On Wed, Nov 17, 2010 at 5:22 AM, Josef Bacik <josef@redhat.com> wr=
ote:
> >> > There is a bug in find_free_extent where if we don't find a free=
 extent in the
> >> > raid type we are looking for, we loop through to the next raid t=
ype. =C2=A0This is
> >> > not ok since we need to make sure we honor the raid types we are=
 given. =C2=A0So
> >> > instead kill this check and get the proper index for the raid ty=
pe we want from
> >> > the allocator. =C2=A0Thanks,
> >> >
> >>
> >> Loop through raid types is for handling failure in the middle of r=
aid type
> >> conversion.
> >
> > The problem is that nothing prevents it from looping back to a raid=
0
> > chunk when we really want raid1 or raid10. =C2=A0And mkfs leaves be=
hind a
> > small raid0 chunk (4MB) that is uses as it assembles all the device=
s.
>=20
> check code at end of btrfs_read_block_groups, it prevents allocating
> from raid0 when there are mirrored block groups.

We're still allocating from them though.  It's a big problem when we
mount degraded.

-chris

>=20
> >
> > I confirmed that we often use the small raid0 chunk even in raid1 o=
r
> > raid10.
> >
> > Please take a look at this commit:
> >
> > http://git.kernel.org/?p=3Dlinux/kernel/git/mason/btrfs-unstable.gi=
t;a=3Dcommit;h=3D83a50de97fe96aca82389e061862ed760ece2283
> >
> > -chris
> > --
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