Re: [PATCH] xfs: truncate transaction does not modify the inobt

[Amir Goldstein <amir73il@gmail.com>]

On Wed, Nov 7, 2018 at 7:18 AM Darrick J. Wong <darrick.wong@oracle.com> wrote:
>
> On Wed, Nov 07, 2018 at 07:09:42AM +0200, Amir Goldstein wrote:
> > On Mon, Nov 5, 2018 at 7:57 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > >
> > > On Sat, Nov 3, 2018 at 7:15 PM Amir Goldstein <amir73il@gmail.com> wrote:
> > > >
> > > > From: Brian Foster <bfoster@redhat.com>
> > > >
> > > > The truncate transaction does not ever modify the inode btree, but
> > > > includes an associated log reservation. Update
> > > > xfs_calc_itruncate_reservation() to remove the reservation
> > > > associated with inobt updates.
> > > >
> > > > [Amir:  This commit was merged for kernel v4.16 and a twin commit was
> > > >         merged for xfsprogs v4.16. As a result, a small xfs filesystem
> > > >         formatted with features -m rmapbt=1,reflink=1 using mkfs.xfs
> > > >         version >= v4.16 cannot be mounted with kernel < v4.16.
> > > >
> > > >         For example, xfstests generic/17{1,2,3} format a small fs and
> > > >         when trying to mount it, they fail with an assert on this very
> > > >         demonic line:
> > > >
> > > >  XFS (vdc): Log size 3075 blocks too small, minimum size is 3717 blocks
> > > >  XFS (vdc): AAIEEE! Log failed size checks. Abort!
> > > >  XFS: Assertion failed: 0, file: src/linux/fs/xfs/xfs_log.c, line: 666
> > > >
> > > >         The simple solution for stable kernels is to apply this patch,
> > > >         because mkfs.xfs v4.16 is already in the wild, so we have to
> > > >         assume that xfs filesystems with a "too small" log exist.
> > > >         Regardless, xfsprogs maintainers should also consider reverting
> > > >         the twin patch to stop creating those filesystems for the sake
> > > >         of users with unpatched kernels.]
> > > >
> > > > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > > > Reviewed-by: Dave Chinner <dchinner@redhat.com>
> > > > Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > > Cc: <stable@vger.kernel.org> # v4.9+
> > > > Signed-off-by: Amir Goldstein <amir73il@gmail.com>
> > > > ---
> > > >
> > > > Darrick/Dave,
> > > >
> > > > It took me a while to figure out what was going on with my test systems
> > > > when small test partitions (10G) stopped working with older kernels.
> > > >
> > > > Please bless this change for stable and consider the remedie for mkfs.xfs
> > > > I verified that patch cleanly applies to stable kernels 4.14.y and 4.9.y
> > > > and that I can mount a filsystem created with new mkfs.xfs.
> > > >
> > > > I am now running quick tests on stable 4.14.y with configs 4k, 1k,
> > > > reflink,reflink+overlay to verify no regressions from this patch.
> > > >
> > >
> > > FYI no regressions detected.
> > >
> > > Thoughts?
> > >
> >
> > Maybe you'd want to chalk it up to reflink/rmapbt being Experimental
> > before kernel 4.16? so the change in "minimum log size" is an on-disk format
> > change prior to removing the Experimental label??
>
> TBH nobody should be using reflink/rmap on 4.14 kernels, ever. :D

I agree, as these error messages try to express:
[    4.982926] XFS (vdd): EXPERIMENTAL reverse mapping btree feature
enabled. Use at your own risk!
[    4.984843] XFS (vdd): EXPERIMENTAL reflink feature enabled. Use at
your own risk!
[    4.987259] XFS (vdd): Log size 3693 blocks too small, minimum size
is 4473 blocks

But it is still a regression, because as I understand some where using
reflink back from
stable 4.9, while it was still maintained...

>
> That said... does it change the minimum log size for (finobt, !reflink,
> !rmap) filesystems?  That might be a bigger worry.  I /think/ the

No problem on my systems mounting small fs with (finobt, !reflink,!rmap)
formatted with mkfs.xfs 4.18.

> transaction reservation change is fine, though I defer to Amir on
> testing... :)
>

Testing passed as I wrote, for configs 4k,1k,reflink,reflink+overlay.

Sasha, please consider the fix patch for 4.14.y,4.9.y.

Thanks,
Amir.