Btrfs: Optimize locking in btrfs_next_leaf()
btrfs_next_leaf was using blocking locks when it could have been using
faster spinning ones instead. This adds a few extra checks around
the pieces that block and switches over to spinning locks.
Signed-off-by: Chris Mason <chris.mason@oracle.com>
diff --git a/fs/btrfs/ctree.c b/fs/btrfs/ctree.c
index 271b05e..b808276 100644
--- a/fs/btrfs/ctree.c
+++ b/fs/btrfs/ctree.c
@@ -4127,28 +4127,44 @@
int btrfs_next_leaf(struct btrfs_root *root, struct btrfs_path *path)
{
int slot;
- int level = 1;
+ int level;
struct extent_buffer *c;
- struct extent_buffer *next = NULL;
+ struct extent_buffer *next;
struct btrfs_key key;
u32 nritems;
int ret;
+ int old_spinning = path->leave_spinning;
+ int force_blocking = 0;
nritems = btrfs_header_nritems(path->nodes[0]);
if (nritems == 0)
return 1;
- btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
+ /*
+ * we take the blocks in an order that upsets lockdep. Using
+ * blocking mode is the only way around it.
+ */
+#ifdef CONFIG_DEBUG_LOCK_ALLOC
+ force_blocking = 1;
+#endif
+ btrfs_item_key_to_cpu(path->nodes[0], &key, nritems - 1);
+again:
+ level = 1;
+ next = NULL;
btrfs_release_path(root, path);
+
path->keep_locks = 1;
+
+ if (!force_blocking)
+ path->leave_spinning = 1;
+
ret = btrfs_search_slot(NULL, root, &key, path, 0, 0);
path->keep_locks = 0;
if (ret < 0)
return ret;
- btrfs_set_path_blocking(path);
nritems = btrfs_header_nritems(path->nodes[0]);
/*
* by releasing the path above we dropped all our locks. A balance
@@ -4158,19 +4174,24 @@
*/
if (nritems > 0 && path->slots[0] < nritems - 1) {
path->slots[0]++;
+ ret = 0;
goto done;
}
while (level < BTRFS_MAX_LEVEL) {
- if (!path->nodes[level])
- return 1;
+ if (!path->nodes[level]) {
+ ret = 1;
+ goto done;
+ }
slot = path->slots[level] + 1;
c = path->nodes[level];
if (slot >= btrfs_header_nritems(c)) {
level++;
- if (level == BTRFS_MAX_LEVEL)
- return 1;
+ if (level == BTRFS_MAX_LEVEL) {
+ ret = 1;
+ goto done;
+ }
continue;
}
@@ -4179,16 +4200,22 @@
free_extent_buffer(next);
}
- /* the path was set to blocking above */
- if (level == 1 && (path->locks[1] || path->skip_locking) &&
- path->reada)
- reada_for_search(root, path, level, slot, 0);
+ next = c;
+ ret = read_block_for_search(NULL, root, path, &next, level,
+ slot, &key);
+ if (ret == -EAGAIN)
+ goto again;
- next = read_node_slot(root, c, slot);
if (!path->skip_locking) {
- btrfs_assert_tree_locked(c);
- btrfs_tree_lock(next);
- btrfs_set_lock_blocking(next);
+ ret = btrfs_try_spin_lock(next);
+ if (!ret) {
+ btrfs_set_path_blocking(path);
+ btrfs_tree_lock(next);
+ if (!force_blocking)
+ btrfs_clear_path_blocking(path, next);
+ }
+ if (force_blocking)
+ btrfs_set_lock_blocking(next);
}
break;
}
@@ -4198,27 +4225,42 @@
c = path->nodes[level];
if (path->locks[level])
btrfs_tree_unlock(c);
+
free_extent_buffer(c);
path->nodes[level] = next;
path->slots[level] = 0;
if (!path->skip_locking)
path->locks[level] = 1;
+
if (!level)
break;
- btrfs_set_path_blocking(path);
- if (level == 1 && path->locks[1] && path->reada)
- reada_for_search(root, path, level, slot, 0);
- next = read_node_slot(root, next, 0);
+ ret = read_block_for_search(NULL, root, path, &next, level,
+ 0, &key);
+ if (ret == -EAGAIN)
+ goto again;
+
if (!path->skip_locking) {
btrfs_assert_tree_locked(path->nodes[level]);
- btrfs_tree_lock(next);
- btrfs_set_lock_blocking(next);
+ ret = btrfs_try_spin_lock(next);
+ if (!ret) {
+ btrfs_set_path_blocking(path);
+ btrfs_tree_lock(next);
+ if (!force_blocking)
+ btrfs_clear_path_blocking(path, next);
+ }
+ if (force_blocking)
+ btrfs_set_lock_blocking(next);
}
}
+ ret = 0;
done:
unlock_up(path, 0, 1);
- return 0;
+ path->leave_spinning = old_spinning;
+ if (!old_spinning)
+ btrfs_set_path_blocking(path);
+
+ return ret;
}
/*