diff --git a/fs/xfs/xfs_file.c b/fs/xfs/xfs_file.c
index 9961d4b5efbe..64278f8acaee 100644
--- a/fs/xfs/xfs_file.c
+++ b/fs/xfs/xfs_file.c
@@ -39,33 +39,25 @@ static const struct vm_operations_struct xfs_file_vm_ops;
  * Decide if the given file range is aligned to the size of the fundamental
  * allocation unit for the file.
  */
-static bool
+bool
 xfs_is_falloc_aligned(
 	struct xfs_inode	*ip,
 	loff_t			pos,
 	long long int		len)
 {
-	struct xfs_mount	*mp = ip->i_mount;
-	uint64_t		mask;
+	unsigned int		alloc_unit = xfs_inode_alloc_unitsize(ip);
 
-	if (XFS_IS_REALTIME_INODE(ip)) {
-		if (!is_power_of_2(mp->m_sb.sb_rextsize)) {
-			u64	rextbytes;
-			u32	mod;
+	if (!is_power_of_2(alloc_unit)) {
+		u32	mod;
 
-			rextbytes = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize);
-			div_u64_rem(pos, rextbytes, &mod);
-			if (mod)
-				return false;
-			div_u64_rem(len, rextbytes, &mod);
-			return mod == 0;
-		}
-		mask = XFS_FSB_TO_B(mp, mp->m_sb.sb_rextsize) - 1;
-	} else {
-		mask = mp->m_sb.sb_blocksize - 1;
+		div_u64_rem(pos, alloc_unit, &mod);
+		if (mod)
+			return false;
+		div_u64_rem(len, alloc_unit, &mod);
+		return mod == 0;
 	}
 
-	return !((pos | len) & mask);
+	return !((pos | len) & (alloc_unit - 1));
 }
 
 /*
diff --git a/fs/xfs/xfs_file.h b/fs/xfs/xfs_file.h
index 7d39e3eca56d..2ad91f755caf 100644
--- a/fs/xfs/xfs_file.h
+++ b/fs/xfs/xfs_file.h
@@ -9,4 +9,7 @@
 extern const struct file_operations xfs_file_operations;
 extern const struct file_operations xfs_dir_file_operations;
 
+bool xfs_is_falloc_aligned(struct xfs_inode *ip, loff_t pos,
+		long long int len);
+
 #endif /* __XFS_FILE_H__ */
diff --git a/fs/xfs/xfs_inode.c b/fs/xfs/xfs_inode.c
index 39e6f88e9691..492dae0efad2 100644
--- a/fs/xfs/xfs_inode.c
+++ b/fs/xfs/xfs_inode.c
@@ -4008,3 +4008,16 @@ xfs_break_layouts(
 
 	return error;
 }
+
+/* Returns the size of fundamental allocation unit for a file, in bytes. */
+unsigned int
+xfs_inode_alloc_unitsize(
+	struct xfs_inode	*ip)
+{
+	unsigned int		blocks = 1;
+
+	if (XFS_IS_REALTIME_INODE(ip))
+		blocks = ip->i_mount->m_sb.sb_rextsize;
+
+	return XFS_FSB_TO_B(ip->i_mount, blocks);
+}
diff --git a/fs/xfs/xfs_inode.h b/fs/xfs/xfs_inode.h
index b2dde0e0f265..fa3e605901e2 100644
--- a/fs/xfs/xfs_inode.h
+++ b/fs/xfs/xfs_inode.h
@@ -625,6 +625,7 @@ int xfs_inode_reload_unlinked(struct xfs_inode *ip);
 bool xfs_ifork_zapped(const struct xfs_inode *ip, int whichfork);
 void xfs_inode_count_blocks(struct xfs_trans *tp, struct xfs_inode *ip,
 		xfs_filblks_t *dblocks, xfs_filblks_t *rblocks);
+unsigned int xfs_inode_alloc_unitsize(struct xfs_inode *ip);
 
 struct xfs_dir_update_params {
 	const struct xfs_inode	*dp;