Btrfs: optimize btrfs_lookup_extent_info()

If we're looking for a metadata item in the tree and the
search fails with return value of 1, and the slot doesn't
point to the first item in the leaf, check if the previous
item in the leaf corresponds to an extent item for the same
object id - if it does, then don't do another tree search
to get it.

This optimization is already done by btrfs-progs.

V2: updated commit message.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 7e172c6dba68f52a726fbfeba7df3c3887051adf..3e7e05e6156f65b7d762e6c2f3332786d165d664 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -771,10 +771,23 @@ again:
                goto out_free;
 
        if (ret > 0 && metadata && key.type == BTRFS_METADATA_ITEM_KEY) {
-               key.type = BTRFS_EXTENT_ITEM_KEY;
-               key.offset = root->leafsize;
-               btrfs_release_path(path);
-               goto again;
+               metadata = 0;
+               if (path->slots[0]) {
+                       path->slots[0]--;
+                       btrfs_item_key_to_cpu(path->nodes[0], &key,
+                                             path->slots[0]);
+                       if (key.objectid == bytenr &&
+                           key.type == BTRFS_EXTENT_ITEM_KEY &&
+                           key.offset == root->leafsize)
+                               ret = 0;
+               }
+               if (ret) {
+                       key.objectid = bytenr;
+                       key.type = BTRFS_EXTENT_ITEM_KEY;
+                       key.offset = root->leafsize;
+                       btrfs_release_path(path);
+                       goto again;
+               }
        }
 
        if (ret == 0) {