btrfs: make space cache inode readahead failure nonfatal

We do a readahead of the free space cache inode to speed things up but
the failure is not fatal, like in other readahead cases. Proper reads
would need to happen anyway and any errors would be caught there.
Reviewed-by: Liu Bo <bo.li.liu@oracle.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/free-space-cache.c

@@ -286,14 +286,14 @@ int btrfs_truncate_free_space_cache(struct btrfs_root *root,
 	return ret;
 }
 
-static int readahead_cache(struct inode *inode)
+static void readahead_cache(struct inode *inode)
 {
 	struct file_ra_state *ra;
 	unsigned long last_index;
 
 	ra = kzalloc(sizeof(*ra), GFP_NOFS);
 	if (!ra)
-		return -ENOMEM;
+		return;
 
 	file_ra_state_init(ra, inode->i_mapping);
 	last_index = (i_size_read(inode) - 1) >> PAGE_SHIFT;
@@ -301,8 +301,6 @@ static int readahead_cache(struct inode *inode)
 	page_cache_sync_readahead(inode->i_mapping, ra, NULL, 0, last_index);
 
 	kfree(ra);
-
-	return 0;
 }
 
 static int io_ctl_init(struct btrfs_io_ctl *io_ctl, struct inode *inode,
@@ -730,9 +728,7 @@ static int __load_free_space_cache(struct btrfs_root *root, struct inode *inode,
 	if (ret)
 		return ret;
 
-	ret = readahead_cache(inode);
-	if (ret)
-		goto out;
+	readahead_cache(inode);
 
 	ret = io_ctl_prepare_pages(&io_ctl, inode, 1);
 	if (ret)