xfs: reintroduce reaping of file metadata blocks to xrep_reap_extents

Back in commit a55e07308831b ("xfs: only allow reaping of per-AG
blocks in xrep_reap_extents"), we removed from the reaping code the
ability to handle bmbt blocks. At the time, the reaping code only
walked single blocks, didn't correctly detect crosslinked blocks, and
the special casing made the function hard to understand. It was easier
to remove unneeded functionality prior to fixing all the bugs.

Now that we've fixed the problems, we want again the ability to reap
file metadata blocks. Reintroduce the per-file reaping functionality
atop the current implementation. We require that sc->sa is
uninitialized, so that we can use it to hold all the per-AG context for
a given extent.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>

xfs: use per-AG bitmaps to reap unused AG metadata blocks during repair

The AGFL repair code uses a series of bitmaps to figure out where there
are OWN_AG blocks that are not claimed by the free space and rmap
btrees. These blocks become the new AGFL, and any overflow is reaped.
The bitmaps current track xfs_fsblock_t even though we already know the
AG number.

In the last patch, we introduced a new bitmap "type" for tracking
xfs_agblock_t extents. Port the reaping code and the AGFL repair to use
this new type, which makes it very obvious what we're tracking. This
also eliminates a bunch of unnecessary agblock <-> fsblock conversions.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

xfs: reap large AG metadata extents when possible

When we're freeing extents that have been set in a bitmap, break the
bitmap extent into multiple sub-extents organized by fate, and reap the
extents. This enables us to dispose of old resources more efficiently
than doing them block by block.

While we're at it, rename the reaping functions to make it clear that
they're reaping per-AG extents.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>

xfs: move the post-repair block reaping code to a separate file

Reaping blocks after a repair is a complicated affair involving a lot of
rmap btree lookups and figuring out if we're going to unmap or free old
metadata blocks that might be crosslinked. Eventually, we will need to
be able to reap per-AG metadata blocks, bmbt blocks from inode forks,
garbage CoW staging extents, and (even later) blocks from btrees rooted
in inodes. This results in a lot of reaping code, so we might as well
split that off while it's easy.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Dave Chinner <dchinner@redhat.com>