Re: [PATCH 06/13] xfs: replace iunlink backref lookups with list lookups

Dave Chinner
2020-08-19T00:52:36Z

On Tue, Aug 18, 2020 at 05:13:22PM -0700, Darrick J. Wong wrote:
> On Wed, Aug 12, 2020 at 07:25:49PM +1000, Dave Chinner wrote:
> > From: Dave Chinner <dchinner@redhat.com>
> >
> > Now we have an in memory linked list of all the inodes on the
> > unlinked list, use that to look up inodes in the list that we need
> > to modify when adding or removing from the list.
> >
> > This means we are no longer using the backref cache to maintain the
> > previous inode lookups, so we can remove all that infrastructure
> > now.
> >
> > Signed-off-by: Dave Chinner <dchinner@redhat.com>

....

> > @@ -2354,70 +2186,24 @@ xfs_iunlink_map_prev(
> > xfs_agnumber_t agno,
> > xfs_agino_t head_agino,
> > xfs_agino_t target_agino,
> > - xfs_agino_t *agino,
> > + xfs_agino_t agino,
> > struct xfs_imap *imap,
> > struct xfs_dinode **dipp,
> > struct xfs_buf **bpp,
> > struct xfs_perag *pag)
> > {
> > - struct xfs_mount *mp = tp->t_mountp;
> > - xfs_agino_t next_agino;
> > int error;
> >
> > ASSERT(head_agino != target_agino);
> > *bpp = NULL;
> >
> > - /* See if our backref cache can find it faster. */
> > - *agino = xfs_iunlink_lookup_backref(pag, target_agino);
> > - if (*agino != NULLAGINO) {
> > - error = xfs_iunlink_map_ino(tp, agno, *agino, imap, dipp, bpp);
> > - if (error)
> > - return error;
> > -
> > - if (be32_to_cpu((*dipp)->di_next_unlinked) == target_agino)
> > - return 0;
> > -
> > - /*
> > - * If we get here the cache contents were corrupt, so drop the
> > - * buffer and fall back to walking the bucket list.
> > - */
> > - xfs_trans_brelse(tp, *bpp);
> > - *bpp = NULL;
> > - WARN_ON_ONCE(1);
> > - }
> > -
> > - trace_xfs_iunlink_map_prev_fallback(mp, agno);
> > -
> > - /* Otherwise, walk the entire bucket until we find it. */
> > - next_agino = head_agino;
> > - while (next_agino != target_agino) {
> > - xfs_agino_t unlinked_agino;
> > -
> > - if (*bpp)
> > - xfs_trans_brelse(tp, *bpp);
> > -
> > - *agino = next_agino;
> > - error = xfs_iunlink_map_ino(tp, agno, next_agino, imap, dipp,
> > - bpp);
> > - if (error)
> > - return error;
> > -
> > - unlinked_agino = be32_to_cpu((*dipp)->di_next_unlinked);
> > - /*
> > - * Make sure this pointer is valid and isn't an obvious
> > - * infinite loop.
> > - */
> > - if (!xfs_verify_agino(mp, agno, unlinked_agino) ||
> > - next_agino == unlinked_agino) {
> > - XFS_CORRUPTION_ERROR(__func__,
> > - XFS_ERRLEVEL_LOW, mp,
> > - *dipp, sizeof(**dipp));
> > - error = -EFSCORRUPTED;
> > - return error;
> > - }
> > - next_agino = unlinked_agino;
> > - }
> > + ASSERT(agino != NULLAGINO);
> > + error = xfs_iunlink_map_ino(tp, agno, agino, imap, dipp, bpp);
> > + if (error)
> > + return error;
> >
> > + if (be32_to_cpu((*dipp)->di_next_unlinked) != target_agino)
> > + return -EFSCORRUPTED;
>
> Why drop the corruption report here?

For simplicity of refactoring. It comes back later on in the series
as this check gets recombined with another similar function. i.e.
See xfs_iunlink_log_inode() at the end of the series....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com