[PATCH v2] Btrfs: faster file extent item search in clone ioctl

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

When we are looking for file extent items that intersect the cloning
range, for each one that falls completely outside the range, don't
release the path and do another full tree search - just move on
to the next slot and copy the file extent item into our buffer only
if the item intersects the cloning range.
Also leave the btree node/leaf locks in spinning mode to not make other
tasks sleep since we process each leaf very quickly.

Signed-off-by: Filipe David Borba Manana <fdmanana@gmail.com>
---

V2: Set path->leave_spinning to 1.

 fs/btrfs/ioctl.c |   23 +++++++++++++----------
 1 file changed, 13 insertions(+), 10 deletions(-)

diff --git a/fs/btrfs/ioctl.c b/fs/btrfs/ioctl.c
index 3970f32..e3b72da 100644
--- a/fs/btrfs/ioctl.c
+++ b/fs/btrfs/ioctl.c
@@ -2893,7 +2893,7 @@ static int btrfs_clone(struct inode *src, struct inode *inode,
 		vfree(buf);
 		return ret;
 	}
-
+	path->leave_spinning = 1;
 	path->reada = 2;
 	/* clone data */
 	key.objectid = btrfs_ino(src);
@@ -2911,6 +2911,7 @@ static int btrfs_clone(struct inode *src, struct inode *inode,
 			goto out;
 
 		nritems = btrfs_header_nritems(path->nodes[0]);
+process_slot:
 		if (path->slots[0] >= nritems) {
 			ret = btrfs_next_leaf(BTRFS_I(src)->root, path);
 			if (ret < 0)
@@ -2937,11 +2938,6 @@ static int btrfs_clone(struct inode *src, struct inode *inode,
 			u8 comp;
 			u64 endoff;
 
-			size = btrfs_item_size_nr(leaf, slot);
-			read_extent_buffer(leaf, buf,
-					   btrfs_item_ptr_offset(leaf, slot),
-					   size);
-
 			extent = btrfs_item_ptr(leaf, slot,
 						struct btrfs_file_extent_item);
 			comp = btrfs_file_extent_compression(leaf, extent);
@@ -2960,11 +2956,19 @@ static int btrfs_clone(struct inode *src, struct inode *inode,
 				datal = btrfs_file_extent_ram_bytes(leaf,
 								    extent);
 			}
-			btrfs_release_path(path);
 
 			if (key.offset + datal <= off ||
-			    key.offset >= off + len - 1)
-				goto next;
+			    key.offset >= off + len - 1) {
+				path->slots[0]++;
+				goto process_slot;
+			}
+
+			size = btrfs_item_size_nr(leaf, slot);
+			read_extent_buffer(leaf, buf,
+					   btrfs_item_ptr_offset(leaf, slot),
+					   size);
+
+			btrfs_release_path(path);
 
 			memcpy(&new_key, &key, sizeof(new_key));
 			new_key.objectid = btrfs_ino(inode);
@@ -3135,7 +3139,6 @@ static int btrfs_clone(struct inode *src, struct inode *inode,
 			}
 			ret = btrfs_end_transaction(trans, root);
 		}
-next:
 		btrfs_release_path(path);
 		key.offset++;
 	}
-- 
1.7.9.5