Btrfs: optimize function btrfs_read_chunk_tree

After reading all device items from the chunk tree, don't
exit the loop and then navigate down the tree again to find
the chunk items. Instead just read all device items and
chunk items with a single tree search. This is possible
because all device items are found before any chunk item in
the chunks tree.

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

diff --git a/fs/btrfs/volumes.c b/fs/btrfs/volumes.c
index 557a7438f92941d142e6f613e0b2e9ee67c09055..93f39b1e71737582111797790392715623f55fee 100644 (file)
--- a/fs/btrfs/volumes.c
+++ b/fs/btrfs/volumes.c
@@ -5646,14 +5646,15 @@ int btrfs_read_chunk_tree(struct btrfs_root *root)
        mutex_lock(&uuid_mutex);
        lock_chunks(root);
 
-       /* first we search for all of the device items, and then we
-        * read in all of the chunk items.  This way we can create chunk
-        * mappings that reference all of the devices that are afound
+       /*
+        * Read all device items, and then all the chunk items. All
+        * device items are found before any chunk item (their object id
+        * is smaller than the lowest possible object id for a chunk
+        * item - BTRFS_FIRST_CHUNK_TREE_OBJECTID).
         */
        key.objectid = BTRFS_DEV_ITEMS_OBJECTID;
        key.offset = 0;
        key.type = 0;
-again:
        ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
        if (ret < 0)
                goto error;
@@ -5669,17 +5670,13 @@ again:
                        break;
                }
                btrfs_item_key_to_cpu(leaf, &found_key, slot);
-               if (key.objectid == BTRFS_DEV_ITEMS_OBJECTID) {
-                       if (found_key.objectid != BTRFS_DEV_ITEMS_OBJECTID)
-                               break;
-                       if (found_key.type == BTRFS_DEV_ITEM_KEY) {
-                               struct btrfs_dev_item *dev_item;
-                               dev_item = btrfs_item_ptr(leaf, slot,
+               if (found_key.type == BTRFS_DEV_ITEM_KEY) {
+                       struct btrfs_dev_item *dev_item;
+                       dev_item = btrfs_item_ptr(leaf, slot,
                                                  struct btrfs_dev_item);
-                               ret = read_one_dev(root, leaf, dev_item);
-                               if (ret)
-                                       goto error;
-                       }
+                       ret = read_one_dev(root, leaf, dev_item);
+                       if (ret)
+                               goto error;
                } else if (found_key.type == BTRFS_CHUNK_ITEM_KEY) {
                        struct btrfs_chunk *chunk;
                        chunk = btrfs_item_ptr(leaf, slot, struct btrfs_chunk);
@@ -5689,11 +5686,6 @@ again:
                }
                path->slots[0]++;
        }
-       if (key.objectid == BTRFS_DEV_ITEMS_OBJECTID) {
-               key.objectid = 0;
-               btrfs_release_path(path);
-               goto again;
-       }
        ret = 0;
 error:
        unlock_chunks(root);