xfs: xfs_alloc_fix_freelist() can use incore perag structures

At the moment, xfs_alloc_fix_freelist() uses a mix of per-ag based
access and agf buffer  based access to freelist and space usage
information. However, once the AGF buffer is locked inside this
function, it is guaranteed that both the in-memory and on-disk
values are identical. xfs_alloc_fix_freelist() doesn't modify the
values in the structures directly, so it is a read-only user of the
infomration, and hence can use the per-ag structure exclusively for
determining what it should do.

This opens up an avenue for cleaning up a lot of duplicated logic
whose only difference is the structure it gets the data from, and in
doing so removes a lot of needless byte swapping overhead when
fixing up the free list.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_filestream.c b/fs/xfs/xfs_filestream.c
index da82f1c..9ac5eaa 100644
--- a/fs/xfs/xfs_filestream.c
+++ b/fs/xfs/xfs_filestream.c
@@ -196,7 +196,8 @@
 			goto next_ag;
 		}
 
-		longest = xfs_alloc_longest_free_extent(mp, pag);
+		longest = xfs_alloc_longest_free_extent(mp, pag,
+						XFS_MIN_FREELIST_PAG(pag, mp));
 		if (((minlen && longest >= minlen) ||
 		     (!minlen && pag->pagf_freeblks >= minfree)) &&
 		    (!pag->pagf_metadata || !(flags & XFS_PICK_USERDATA) ||