[PATCH] Btrfs: optimize extent item search in run_delayed_extent_op

[Filipe David Borba Manana <fdmanana@gmail.com>]

Instead of doing another extent tree search if the first search failed
to find a metadata item, check if the previous item in the leaf is an
extent item and use it if it is, otherwise do the second tree search
for an extent item.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
---
 fs/btrfs/extent-tree.c |   27 ++++++++++++++++++++-------
 1 file changed, 20 insertions(+), 7 deletions(-)

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 9be5e35..7baefe4 100644
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -2138,15 +2138,28 @@ again:
 	}
 	if (ret > 0) {
 		if (metadata) {
-			btrfs_release_path(path);
-			metadata = 0;
+			if (path->slots[0] > 0) {
+				path->slots[0]--;
+				btrfs_item_key_to_cpu(path->nodes[0], &key,
+						      path->slots[0]);
+				if (key.objectid == node->bytenr &&
+				    key.type == BTRFS_EXTENT_ITEM_KEY &&
+				    key.offset == node->num_bytes)
+					ret = 0;
+			}
+			if (ret > 0) {
+				btrfs_release_path(path);
+				metadata = 0;
 
-			key.offset = node->num_bytes;
-			key.type = BTRFS_EXTENT_ITEM_KEY;
-			goto again;
+				key.objectid = node->bytenr;
+				key.offset = node->num_bytes;
+				key.type = BTRFS_EXTENT_ITEM_KEY;
+				goto again;
+			}
+		} else {
+			err = -EIO;
+			goto out;
 		}
-		err = -EIO;
-		goto out;
 	}
 
 	leaf = path->nodes[0];
-- 
1.7.9.5