diff --git a/fs/xfs/xfs_bmap_util.c b/fs/xfs/xfs_bmap_util.c
index c83f549dc17b9dcf9e22631e099a23b2d377b7da..e0a442f504e5e3d162e90cb2dc66b061dcf38a26 100644
--- a/fs/xfs/xfs_bmap_util.c
+++ b/fs/xfs/xfs_bmap_util.c
@@ -1899,17 +1899,28 @@ xfs_swap_extents(
 	 * performed with log redo items!
 	 */
 	if (xfs_sb_version_hasrmapbt(&mp->m_sb)) {
+		int		w	= XFS_DATA_FORK;
+		uint32_t	ipnext	= XFS_IFORK_NEXTENTS(ip, w);
+		uint32_t	tipnext	= XFS_IFORK_NEXTENTS(tip, w);
+
+		/*
+		 * Conceptually this shouldn't affect the shape of either bmbt,
+		 * but since we atomically move extents one by one, we reserve
+		 * enough space to rebuild both trees.
+		 */
+		resblks = XFS_SWAP_RMAP_SPACE_RES(mp, ipnext, w);
+		resblks +=  XFS_SWAP_RMAP_SPACE_RES(mp, tipnext, w);
+
 		/*
-		 * Conceptually this shouldn't affect the shape of either
-		 * bmbt, but since we atomically move extents one by one,
-		 * we reserve enough space to rebuild both trees.
+		 * Handle the corner case where either inode might straddle the
+		 * btree format boundary. If so, the inode could bounce between
+		 * btree <-> extent format on unmap -> remap cycles, freeing and
+		 * allocating a bmapbt block each time.
 		 */
-		resblks = XFS_SWAP_RMAP_SPACE_RES(mp,
-				XFS_IFORK_NEXTENTS(ip, XFS_DATA_FORK),
-				XFS_DATA_FORK) +
-			  XFS_SWAP_RMAP_SPACE_RES(mp,
-				XFS_IFORK_NEXTENTS(tip, XFS_DATA_FORK),
-				XFS_DATA_FORK);
+		if (ipnext == (XFS_IFORK_MAXEXT(ip, w) + 1))
+			resblks += XFS_IFORK_MAXEXT(ip, w);
+		if (tipnext == (XFS_IFORK_MAXEXT(tip, w) + 1))
+			resblks += XFS_IFORK_MAXEXT(tip, w);
 	}
 	error = xfs_trans_alloc(mp, &M_RES(mp)->tr_write, resblks, 0, 0, &tp);
 	if (error)