xfs: clean up XFS_MIN_FREELIST macros

We no longer calculate the minimum freelist size from the on-disk
AGF, so we don't need the macros used for this. That means the
nested macros can be cleaned up, and turn this into an actual
function so the logic is clear and concise. This will make it much
easier to add support for the rmap btree when the time comes.

This also gets rid of the XFS_AG_MAXLEVELS macro used by these
freelist macros as it is simply a wrapper around a single variable.

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/libxfs/xfs_alloc.c b/fs/xfs/libxfs/xfs_alloc.c
index 2afa6bc..0290781 100644
--- a/fs/xfs/libxfs/xfs_alloc.c
+++ b/fs/xfs/libxfs/xfs_alloc.c
@@ -1838,6 +1838,23 @@
 	return pag->pagf_flcount > 0 || pag->pagf_longest > 0;
 }
 
+unsigned int
+xfs_alloc_min_freelist(
+	struct xfs_mount	*mp,
+	struct xfs_perag	*pag)
+{
+	unsigned int		min_free;
+
+	/* space needed by-bno freespace btree */
+	min_free = min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_BNOi] + 1,
+				       mp->m_ag_maxlevels);
+	/* space needed by-size freespace btree */
+	min_free += min_t(unsigned int, pag->pagf_levels[XFS_BTNUM_CNTi] + 1,
+				       mp->m_ag_maxlevels);
+
+	return min_free;
+}
+
 /*
  * Check if the operation we are fixing up the freelist for should go ahead or
  * not. If we are freeing blocks, we always allow it, otherwise the allocation
@@ -1912,7 +1929,7 @@
 		goto out_agbp_relse;
 	}
 
-	need = XFS_MIN_FREELIST_PAG(pag, mp);
+	need = xfs_alloc_min_freelist(mp, pag);
 	if (!xfs_alloc_space_available(args, need, flags))
 		goto out_agbp_relse;
 
@@ -1931,9 +1948,8 @@
 		}
 	}
 
-
 	/* If there isn't enough total space or single-extent, reject it. */
-	need = XFS_MIN_FREELIST_PAG(pag, mp);
+	need = xfs_alloc_min_freelist(mp, pag);
 	if (!xfs_alloc_space_available(args, need, flags))
 		goto out_agbp_relse;