Btrfs: try to avoid acquiring free space ctl's lock

We don't need to take the lock if the block group has not been cached.

Signed-off-by: Liu Bo <bo.li.liu@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

diff --git a/fs/btrfs/extent-tree.c b/fs/btrfs/extent-tree.c
index 0992cd1393a6da4a3308577a6e21ac4a51d4d05f..85109de0e14090771c1aa63d2a6c5b259ea2aefd 100644 (file)
--- a/fs/btrfs/extent-tree.c
+++ b/fs/btrfs/extent-tree.c
@@ -7714,18 +7714,20 @@ unclustered_alloc:
                        last_ptr->fragmented = 1;
                        spin_unlock(&last_ptr->lock);
                }
-               spin_lock(&block_group->free_space_ctl->tree_lock);
-               if (cached &&
-                   block_group->free_space_ctl->free_space <
-                   num_bytes + empty_cluster + empty_size) {
-                       if (block_group->free_space_ctl->free_space >
-                           max_extent_size)
-                               max_extent_size =
-                                       block_group->free_space_ctl->free_space;
-                       spin_unlock(&block_group->free_space_ctl->tree_lock);
-                       goto loop;
+               if (cached) {
+                       struct btrfs_free_space_ctl *ctl =
+                               block_group->free_space_ctl;
+
+                       spin_lock(&ctl->tree_lock);
+                       if (ctl->free_space <
+                           num_bytes + empty_cluster + empty_size) {
+                               if (ctl->free_space > max_extent_size)
+                                       max_extent_size = ctl->free_space;
+                               spin_unlock(&ctl->tree_lock);
+                               goto loop;
+                       }
+                       spin_unlock(&ctl->tree_lock);
                }
-               spin_unlock(&block_group->free_space_ctl->tree_lock);
 
                offset = btrfs_find_space_for_alloc(block_group, search_start,
                                                    num_bytes, empty_size,