[PATCH] btrfs: don't search entire range for delalloc with fiemap

[Josef Bacik]

For the case where we have

[EXTENT1][HOLE][EXTENT2]

If we fiemap from [HOLE] we will search to len (which could be -1) to
see if there's any delalloc extents in the range, however in the above
case btrfs_get_extent() returns a hole em for just the range of the
hole, as it will find EXTENT2, so all we need to do is search for
delalloc in the hole range, not the entire rest of the requested fiemap
range.

This fixes the extremely bad fiemap performance with very large sparse
files.

Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
---
 fs/btrfs/inode.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c
index 8fc1e3b6e00c..b7ad8f7a7b53 100644
--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -7095,7 +7095,7 @@ struct extent_map *btrfs_get_extent_fiemap(struct btrfs_inode *inode,
 		hole_em = em;
 
 	/* check to see if we've wrapped (len == -1 or similar) */
-	end = start + len;
+	end = em->start + em->len;
 	if (end < start)
 		end = (u64)-1;
 	else
-- 
2.36.1