xfs: only writeback and truncate pages for the freed range

xfs_free_file_space() only affects the range of the file for which space
is being freed. It currently writes and truncates the page cache from
the start offset of the free to EOF.

Modify xfs_free_file_space() to write back and truncate page cache of
just the range being freed.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

fs/xfs/xfs_bmap_util.c

@@ -1205,6 +1205,7 @@ xfs_free_file_space(
 	xfs_bmap_free_t		free_list;
 	xfs_bmbt_irec_t		imap;
 	xfs_off_t		ioffset;
+	xfs_off_t		iendoffset;
 	xfs_extlen_t		mod=0;
 	xfs_mount_t		*mp;
 	int			nimap;
@@ -1233,12 +1234,13 @@ xfs_free_file_space(
 	inode_dio_wait(VFS_I(ip));
 
 	rounding = max_t(xfs_off_t, 1 << mp->m_sb.sb_blocklog, PAGE_CACHE_SIZE);
-	ioffset = offset & ~(rounding - 1);
-	error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping,
-					      ioffset, -1);
+	ioffset = round_down(offset, rounding);
+	iendoffset = round_up(offset + len, rounding) - 1;
+	error = filemap_write_and_wait_range(VFS_I(ip)->i_mapping, ioffset,
+					     iendoffset);
 	if (error)
 		goto out;
-	truncate_pagecache_range(VFS_I(ip), ioffset, -1);
+	truncate_pagecache_range(VFS_I(ip), ioffset, iendoffset);
 
 	/*
 	 * Need to zero the stuff we're not freeing, on disk.