diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index f8a68a2..cfa7a5d 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -207,8 +207,8 @@
 	uint			m_ag_maxlevels;	/* XFS_AG_MAXLEVELS */
 	uint			m_bm_maxlevels[2]; /* XFS_BM_MAXLEVELS */
 	uint			m_in_maxlevels;	/* max inobt btree levels. */
-	struct xfs_perag	*m_perag;	/* per-ag accounting info */
-	struct rw_semaphore	m_peraglock;	/* lock for m_perag (pointer) */
+	struct radix_tree_root	m_perag_tree;	/* per-ag accounting info */
+	spinlock_t		m_perag_lock;	/* lock for m_perag_tree */
 	struct mutex		m_growlock;	/* growfs mutex */
 	int			m_fixedfsid[2];	/* unchanged for life of FS */
 	uint			m_dmevmask;	/* DMI events for this FS */
@@ -389,7 +389,12 @@
 static inline struct xfs_perag *
 xfs_perag_get(struct xfs_mount *mp, xfs_agnumber_t agno)
 {
-	return &mp->m_perag[agno];
+	struct xfs_perag	*pag;
+
+	spin_lock(&mp->m_perag_lock);
+	pag = radix_tree_lookup(&mp->m_perag_tree, agno);
+	spin_unlock(&mp->m_perag_lock);
+	return pag;
 }
 
 static inline void
@@ -450,7 +455,8 @@
 #endif	/* __KERNEL__ */
 
 extern void	xfs_mod_sb(struct xfs_trans *, __int64_t);
-extern xfs_agnumber_t	xfs_initialize_perag(struct xfs_mount *, xfs_agnumber_t);
+extern int	xfs_initialize_perag(struct xfs_mount *, xfs_agnumber_t,
+					xfs_agnumber_t *);
 extern void	xfs_sb_from_disk(struct xfs_sb *, struct xfs_dsb *);
 extern void	xfs_sb_to_disk(struct xfs_dsb *, struct xfs_sb *, __int64_t);