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

["Darrick J. Wong" <darrick.wong@oracle.com>]

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

That said... does it change the minimum log size for (finobt, !reflink,
!rmap) filesystems?  That might be a bigger worry.  I /think/ the
transaction reservation change is fine, though I defer to Amir on
testing... :)

--D

> Thanks,
> Amir.