btrfs: always set extent_io_tree::inode and drop fs_info

The extent_io_tree is embedded in several structures, notably in struct
btrfs_inode.  The fs_info is only used for reporting errors and for
reference in trace points. We can get to the pointer through the inode,
but not all io trees set it. However, we always know the owner and
can recognize if inode is valid.  For access helpers are provided, const
variant for the trace points.

This reduces size of extent_io_tree by 8 bytes and following structures
in turn:

- btrfs_inode		1104 -> 1088
- btrfs_device		 520 ->  512
- btrfs_root		1360 -> 1344
- btrfs_transaction	 456 ->  440
- btrfs_fs_info		3600 -> 3592
- reloc_control		1520 -> 1512

Reviewed-by: Josef Bacik <josef@toxicpanda.com>
Signed-off-by: David Sterba <dsterba@suse.com>

1 files changed, 15 insertions, 3 deletions

diff --git a/fs/btrfs/extent-io-tree.h b/fs/btrfs/extent-io-tree.h
index 5602b0137fcd..ebe6390d65e9 100644
--- a/fs/btrfs/extent-io-tree.h
+++ b/fs/btrfs/extent-io-tree.h
@@ -87,9 +87,17 @@ enum {
 
 struct extent_io_tree {
 	struct rb_root state;
-	struct btrfs_fs_info *fs_info;
-	/* Inode associated with this tree, or NULL. */
-	struct btrfs_inode *inode;
+	/*
+	 * The fs_info is needed for trace points, a tree attached to an inode
+	 * needs the inode.
+	 *
+	 * owner == IO_TREE_INODE_IO - then inode is valid and fs_info can be
+	 *                             accessed as inode->root->fs_info
+	 */
+	union {
+		struct btrfs_fs_info *fs_info;
+		struct btrfs_inode *inode;
+	};
 
 	/* Who owns this io tree, should be one of IO_TREE_* */
 	u8 owner;
@@ -112,6 +120,10 @@ struct extent_state {
 #endif
 };
 
+struct btrfs_inode *extent_io_tree_to_inode(struct extent_io_tree *tree);
+const struct btrfs_inode *extent_io_tree_to_inode_const(const struct extent_io_tree *tree);
+const struct btrfs_fs_info *extent_io_tree_to_fs_info(const struct extent_io_tree *tree);
+
 void extent_io_tree_init(struct btrfs_fs_info *fs_info,
 			 struct extent_io_tree *tree, unsigned int owner);
 void extent_io_tree_release(struct extent_io_tree *tree);