Re: [PATCH] xfs: fix up inode32/64 (re)mount handling

Brian Foster
2016-02-18T12:08:19Z

On Wed, Feb 17, 2016 at 11:51:47PM -0600, Eric Sandeen wrote:
>
>
> On 2/17/16 11:46 PM, Eric Sandeen wrote:
> > On 2/17/16 12:30 PM, Brian Foster wrote:
> >> On Tue, Feb 16, 2016 at 10:47:49PM -0600, Eric Sandeen wrote:
> >>> inode32/inode64 allocator behavior with respect to mount,
> >>> remount and growfs is a little tricky.
> >>>
> >>> The inode32 mount option should only enable the inode32
> >>> allocator heuristics if the filesystem is large enough
> >>> for 64-bit inodes to exist. Today, it has this behavior
> >>> on the initial mount, but a remount with inode32
> >>> unconditionally changes the allocation heuristics, even
> >>> for a small fs.
> >>>
> >>> Also, an inode32 mounted small filesystem should transition
> >>> to the inode32 allocator if the filesystem is subsequently
> >>> grown to a sufficient size. Today that does not happen.
> >>>
> >>> This patch consolidates xfs_set_inode32 and xfs_set_inode64
> >>> into a single new function, and moves the "is the maximum inode
> >>> number big enough to matter" test into that function, so
> >>> it doesn't rely on the caller to get it right - which
> >>> remount did not do, previously.
> >>>
> >>> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> >>> ---
> >>>
> >>> Note, this goes after my token-parsing patch for mount.
> >
> > ...
> >
> >>> @@ -607,54 +619,48 @@ xfs_set_inode32(struct xfs_mount *mp, xfs_agnumber_t agcount)
> >>> max_metadata = agcount;
> >>> }
> >>>
> >>> + /* Get the last possible inode in the filesystem */
> >>> agino = XFS_OFFBNO_TO_AGINO(mp, sbp->sb_agblocks - 1, 0);
> >>> + ino = XFS_AGINO_TO_INO(mp, agcount - 1, agino);
> >>> +
> >>> + /*
> >>> + * If user asked for no more than 32-bit inodes, and the fs is
> >>> + * sufficiently large, set XFS_MOUNT_32BITINODES if we must alter
> >>> + * the allocator to accommodate the request.
> >>> + */
> >>> + if ((mp->m_flags & XFS_MOUNT_SMALL_INUMS) && ino > XFS_MAXINUMBER_32)
> >>> + mp->m_flags |= XFS_MOUNT_32BITINODES;
> >>> + else
> >>> + mp->m_flags &= ~XFS_MOUNT_32BITINODES;
> >>
> >> In the current code, we call into xfs_set_inode64() if
> >> XFS_MOUNT_SMALL_INUMS is not set or it is, but the largest inode is
> >> within XFS_MAXINUMBER_32. In that latter case, xfs_set_inode64() does:
> >>
> >> mp->m_flags &= ~(XFS_MOUNT_32BITINODES |
> >> XFS_MOUNT_SMALL_INUMS);
> >>
> >> ... which I think means we want to clear XFS_MOUNT_SMALL_INUMS along
> >> with XFS_MOUNT_32BITINODES here, yes? The rest looks fine to me:
> >
> > I don't think so; that was a bug, AFAICT.
> >
> > XFS_MOUNT_32BITINODES means that inode32 was specified at mount
>
> Ugh; I had that backwards.
>
> *XFS_MOUNT_SMALL_INUMS* means that inode32 was specified at mount time.
> For the reasons I stated, *that* flag should never be cleared. It
> signifies a specified mount option, which does not go away just because
> the filesystem is currently small.
>
> Maybe we need clearer flag names :/
>

Ah, I missed that part. Sounds good, thanks for the explanation! (And
yes, the flag names are not clear.. ;P)

Brian

> -Eric
>
> > time, i.e. the user wants no more than 32-bit inodes for the
> > duration of this mount.
> >
> > So this is actually a bugfix for the 2nd item mentioned above:
> >
> >>> Also, an inode32 mounted small filesystem should transition
> >>> to the inode32 allocator if the filesystem is subsequently
> >>> grown to a sufficient size. Today that does not happen.
> >
> >> Reviewed-by: Brian Foster <bfoster@redhat.com>
> >
> > Thanks,
> > -Eric
> >
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> >