diff --git a/fs/xfs/libxfs/xfs_btree.c b/fs/xfs/libxfs/xfs_btree.c
index a222f5de2a09..64b47e81f6f3 100644
--- a/fs/xfs/libxfs/xfs_btree.c
+++ b/fs/xfs/libxfs/xfs_btree.c
@@ -4534,6 +4534,40 @@ xfs_btree_compute_maxlevels(
 	return level;
 }
 
+/*
+ * Compute the maximum height of a btree that is allowed to consume up to the
+ * given number of blocks.
+ */
+unsigned int
+xfs_btree_compute_maxlevels_size(
+	unsigned long long	max_btblocks,
+	unsigned int		leaf_mnr)
+{
+	unsigned long long	leaf_blocks = leaf_mnr;
+	unsigned long long	blocks_left;
+	unsigned int		maxlevels;
+
+	if (max_btblocks < 1)
+		return 0;
+
+	/*
+	 * The loop increments maxlevels as long as there would be enough
+	 * blocks left in the reservation to handle each node block at the
+	 * current level pointing to the minimum possible number of leaf blocks
+	 * at the next level down.  We start the loop assuming a single-level
+	 * btree consuming one block.
+	 */
+	maxlevels = 1;
+	blocks_left = max_btblocks - 1;
+	while (leaf_blocks < blocks_left) {
+		maxlevels++;
+		blocks_left -= leaf_blocks;
+		leaf_blocks *= leaf_mnr;
+	}
+
+	return maxlevels;
+}
+
 /*
  * Query a regular btree for all records overlapping a given interval.
  * Start with a LE lookup of the key of low_rec and return all records
diff --git a/fs/xfs/libxfs/xfs_btree.h b/fs/xfs/libxfs/xfs_btree.h
index 1f269bc49714..b848571f999b 100644
--- a/fs/xfs/libxfs/xfs_btree.h
+++ b/fs/xfs/libxfs/xfs_btree.h
@@ -484,6 +484,8 @@ xfs_failaddr_t xfs_btree_lblock_verify(struct xfs_buf *bp,
 		unsigned int max_recs);
 
 uint xfs_btree_compute_maxlevels(uint *limits, unsigned long len);
+unsigned int xfs_btree_compute_maxlevels_size(unsigned long long max_btblocks,
+		unsigned int leaf_mnr);
 unsigned long long xfs_btree_calc_size(uint *limits, unsigned long long len);
 
 /*
diff --git a/fs/xfs/libxfs/xfs_rmap_btree.c b/fs/xfs/libxfs/xfs_rmap_btree.c
index f3c4d0965cc9..85caeb14e4db 100644
--- a/fs/xfs/libxfs/xfs_rmap_btree.c
+++ b/fs/xfs/libxfs/xfs_rmap_btree.c
@@ -535,30 +535,32 @@ xfs_rmapbt_maxrecs(
 }
 
 /* Compute the maximum height of an rmap btree. */
-void
+unsigned int
 xfs_rmapbt_compute_maxlevels(
-	struct xfs_mount		*mp)
+	struct xfs_mount	*mp)
 {
+	if (!xfs_has_reflink(mp)) {
+		/*
+		 * If there's no block sharing, compute the maximum rmapbt
+		 * height assuming one rmap record per AG block.
+		 */
+		return xfs_btree_compute_maxlevels(mp->m_rmap_mnr,
+				mp->m_sb.sb_agblocks);
+	}
+
 	/*
-	 * On a non-reflink filesystem, the maximum number of rmap
-	 * records is the number of blocks in the AG, hence the max
-	 * rmapbt height is log_$maxrecs($agblocks).  However, with
-	 * reflink each AG block can have up to 2^32 (per the refcount
-	 * record format) owners, which means that theoretically we
-	 * could face up to 2^64 rmap records.
+	 * Compute the asymptotic maxlevels for an rmapbt on a reflink fs.
 	 *
-	 * That effectively means that the max rmapbt height must be
-	 * XFS_BTREE_MAXLEVELS.  "Fortunately" we'll run out of AG
-	 * blocks to feed the rmapbt long before the rmapbt reaches
-	 * maximum height.  The reflink code uses ag_resv_critical to
-	 * disallow reflinking when less than 10% of the per-AG metadata
-	 * block reservation since the fallback is a regular file copy.
+	 * On a reflink filesystem, each AG block can have up to 2^32 (per the
+	 * refcount record format) owners, which means that theoretically we
+	 * could face up to 2^64 rmap records.  However, we're likely to run
+	 * out of blocks in the AG long before that happens, which means that
+	 * we must compute the max height based on what the btree will look
+	 * like if it consumes almost all the blocks in the AG due to maximal
+	 * sharing factor.
 	 */
-	if (xfs_has_reflink(mp))
-		mp->m_rmap_maxlevels = XFS_BTREE_MAXLEVELS;
-	else
-		mp->m_rmap_maxlevels = xfs_btree_compute_maxlevels(
-				mp->m_rmap_mnr, mp->m_sb.sb_agblocks);
+	return xfs_btree_compute_maxlevels_size(mp->m_sb.sb_agblocks,
+			mp->m_rmap_mnr[1]);
 }
 
 /* Calculate the refcount btree size for some records. */
diff --git a/fs/xfs/libxfs/xfs_rmap_btree.h b/fs/xfs/libxfs/xfs_rmap_btree.h
index f2eee6572af4..5aaecf755abd 100644
--- a/fs/xfs/libxfs/xfs_rmap_btree.h
+++ b/fs/xfs/libxfs/xfs_rmap_btree.h
@@ -49,7 +49,7 @@ struct xfs_btree_cur *xfs_rmapbt_stage_cursor(struct xfs_mount *mp,
 void xfs_rmapbt_commit_staged_btree(struct xfs_btree_cur *cur,
 		struct xfs_trans *tp, struct xfs_buf *agbp);
 int xfs_rmapbt_maxrecs(int blocklen, int leaf);
-extern void xfs_rmapbt_compute_maxlevels(struct xfs_mount *mp);
+unsigned int xfs_rmapbt_compute_maxlevels(struct xfs_mount *mp);
 
 extern xfs_extlen_t xfs_rmapbt_calc_size(struct xfs_mount *mp,
 		unsigned long long len);
diff --git a/fs/xfs/libxfs/xfs_trans_resv.c b/fs/xfs/libxfs/xfs_trans_resv.c
index 5e300daa2559..679f10e08f31 100644
--- a/fs/xfs/libxfs/xfs_trans_resv.c
+++ b/fs/xfs/libxfs/xfs_trans_resv.c
@@ -814,6 +814,15 @@ xfs_trans_resv_calc(
 	struct xfs_mount	*mp,
 	struct xfs_trans_resv	*resp)
 {
+	unsigned int		rmap_maxlevels = mp->m_rmap_maxlevels;
+
+	/*
+	 * In the early days of rmap+reflink, we hardcoded the rmap maxlevels
+	 * to 9 even if the AG size was smaller.
+	 */
+	if (xfs_has_rmapbt(mp) && xfs_has_reflink(mp))
+		mp->m_rmap_maxlevels = XFS_OLD_REFLINK_RMAP_MAXLEVELS;
+
 	/*
 	 * The following transactions are logged in physical format and
 	 * require a permanent reservation on space.
@@ -916,4 +925,7 @@ xfs_trans_resv_calc(
 	resp->tr_clearagi.tr_logres = xfs_calc_clear_agi_bucket_reservation(mp);
 	resp->tr_growrtzero.tr_logres = xfs_calc_growrtzero_reservation(mp);
 	resp->tr_growrtfree.tr_logres = xfs_calc_growrtfree_reservation(mp);
+
+	/* Put everything back the way it was.  This goes at the end. */
+	mp->m_rmap_maxlevels = rmap_maxlevels;
 }
diff --git a/fs/xfs/libxfs/xfs_trans_space.h b/fs/xfs/libxfs/xfs_trans_space.h
index 50332be34388..440c9c390b86 100644
--- a/fs/xfs/libxfs/xfs_trans_space.h
+++ b/fs/xfs/libxfs/xfs_trans_space.h
@@ -17,6 +17,13 @@
 /* Adding one rmap could split every level up to the top of the tree. */
 #define XFS_RMAPADD_SPACE_RES(mp) ((mp)->m_rmap_maxlevels)
 
+/*
+ * Note that we historically set m_rmap_maxlevels to 9 when reflink was
+ * enabled, so we must preserve this behavior to avoid changing the transaction
+ * space reservations.
+ */
+#define XFS_OLD_REFLINK_RMAP_MAXLEVELS	(9)
+
 /* Blocks we might need to add "b" rmaps to a tree. */
 #define XFS_NRMAPADD_SPACE_RES(mp, b)\
 	(((b + XFS_MAX_CONTIG_RMAPS_PER_BLOCK(mp) - 1) / \
diff --git a/fs/xfs/xfs_mount.c b/fs/xfs/xfs_mount.c
index 06dac09eddbd..e600a0b781c8 100644
--- a/fs/xfs/xfs_mount.c
+++ b/fs/xfs/xfs_mount.c
@@ -635,7 +635,7 @@ xfs_mountfs(
 	xfs_bmap_compute_maxlevels(mp, XFS_DATA_FORK);
 	xfs_bmap_compute_maxlevels(mp, XFS_ATTR_FORK);
 	xfs_mount_setup_inode_geom(mp);
-	xfs_rmapbt_compute_maxlevels(mp);
+	mp->m_rmap_maxlevels = xfs_rmapbt_compute_maxlevels(mp);
 	xfs_refcountbt_compute_maxlevels(mp);
 
 	/*
