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>

fs/btrfs/extent-io-tree.c

@@ -58,12 +58,13 @@ static inline void __btrfs_debug_check_extent_io_range(const char *caller,
 						       struct extent_io_tree *tree,
 						       u64 start, u64 end)
 {
-	struct btrfs_inode *inode = tree->inode;
+	const struct btrfs_inode *inode;
 	u64 isize;
 
-	if (!inode)
+	if (tree->owner != IO_TREE_INODE_IO)
 		return;
 
+	inode = extent_io_tree_to_inode_const(tree);
 	isize = i_size_read(&inode->vfs_inode);
 	if (end >= PAGE_SIZE && (end % 2) == 0 && end != isize - 1) {
 		btrfs_debug_rl(inode->root->fs_info,
@@ -79,13 +80,44 @@ static inline void __btrfs_debug_check_extent_io_range(const char *caller,
 #endif
 
 
+/*
+ * The only tree allowed to set the inode is IO_TREE_INODE_IO.
+ */
+static bool is_inode_io_tree(const struct extent_io_tree *tree)
+{
+	return tree->owner == IO_TREE_INODE_IO;
+}
+
+/* Return the inode if it's valid for the given tree, otherwise NULL. */
+struct btrfs_inode *extent_io_tree_to_inode(struct extent_io_tree *tree)
+{
+	if (tree->owner == IO_TREE_INODE_IO)
+		return tree->inode;
+	return NULL;
+}
+
+/* Read-only access to the inode. */
+const struct btrfs_inode *extent_io_tree_to_inode_const(const struct extent_io_tree *tree)
+{
+	if (tree->owner == IO_TREE_INODE_IO)
+		return tree->inode;
+	return NULL;
+}
+
+/* For read-only access to fs_info. */
+const struct btrfs_fs_info *extent_io_tree_to_fs_info(const struct extent_io_tree *tree)
+{
+	if (tree->owner == IO_TREE_INODE_IO)
+		return tree->inode->root->fs_info;
+	return tree->fs_info;
+}
+
 void extent_io_tree_init(struct btrfs_fs_info *fs_info,
 			 struct extent_io_tree *tree, unsigned int owner)
 {
-	tree->fs_info = fs_info;
 	tree->state = RB_ROOT;
 	spin_lock_init(&tree->lock);
-	tree->inode = NULL;
+	tree->fs_info = fs_info;
 	tree->owner = owner;
 }
 
@@ -318,7 +350,7 @@ static void extent_io_tree_panic(const struct extent_io_tree *tree,
 				 const char *opname,
 				 int err)
 {
-	btrfs_panic(tree->fs_info, err,
+	btrfs_panic(extent_io_tree_to_fs_info(tree), err,
 		    "extent io tree error on %s state start %llu end %llu",
 		    opname, state->start, state->end);
 }
@@ -329,8 +361,9 @@ static void merge_prev_state(struct extent_io_tree *tree, struct extent_state *s
 
 	prev = prev_state(state);
 	if (prev && prev->end == state->start - 1 && prev->state == state->state) {
-		if (tree->inode)
-			btrfs_merge_delalloc_extent(tree->inode, state, prev);
+		if (is_inode_io_tree(tree))
+			btrfs_merge_delalloc_extent(extent_io_tree_to_inode(tree),
+						    state, prev);
 		state->start = prev->start;
 		rb_erase(&prev->rb_node, &tree->state);
 		RB_CLEAR_NODE(&prev->rb_node);
@@ -344,8 +377,9 @@ static void merge_next_state(struct extent_io_tree *tree, struct extent_state *s
 
 	next = next_state(state);
 	if (next && next->start == state->end + 1 && next->state == state->state) {
-		if (tree->inode)
-			btrfs_merge_delalloc_extent(tree->inode, state, next);
+		if (is_inode_io_tree(tree))
+			btrfs_merge_delalloc_extent(extent_io_tree_to_inode(tree),
+						    state, next);
 		state->end = next->end;
 		rb_erase(&next->rb_node, &tree->state);
 		RB_CLEAR_NODE(&next->rb_node);
@@ -378,8 +412,8 @@ static void set_state_bits(struct extent_io_tree *tree,
 	u32 bits_to_set = bits & ~EXTENT_CTLBITS;
 	int ret;
 
-	if (tree->inode)
-		btrfs_set_delalloc_extent(tree->inode, state, bits);
+	if (is_inode_io_tree(tree))
+		btrfs_set_delalloc_extent(extent_io_tree_to_inode(tree), state, bits);
 
 	ret = add_extent_changeset(state, bits_to_set, changeset, 1);
 	BUG_ON(ret < 0);
@@ -424,9 +458,10 @@ static struct extent_state *insert_state(struct extent_io_tree *tree,
 		if (state->end < entry->start) {
 			if (try_merge && end == entry->start &&
 			    state->state == entry->state) {
-				if (tree->inode)
-					btrfs_merge_delalloc_extent(tree->inode,
-								    state, entry);
+				if (is_inode_io_tree(tree))
+					btrfs_merge_delalloc_extent(
+							extent_io_tree_to_inode(tree),
+							state, entry);
 				entry->start = state->start;
 				merge_prev_state(tree, entry);
 				state->state = 0;
@@ -436,9 +471,10 @@ static struct extent_state *insert_state(struct extent_io_tree *tree,
 		} else if (state->end > entry->end) {
 			if (try_merge && entry->end == start &&
 			    state->state == entry->state) {
-				if (tree->inode)
-					btrfs_merge_delalloc_extent(tree->inode,
-								    state, entry);
+				if (is_inode_io_tree(tree))
+					btrfs_merge_delalloc_extent(
+							extent_io_tree_to_inode(tree),
+							state, entry);
 				entry->end = state->end;
 				merge_next_state(tree, entry);
 				state->state = 0;
@@ -490,8 +526,9 @@ static int split_state(struct extent_io_tree *tree, struct extent_state *orig,
 	struct rb_node *parent = NULL;
 	struct rb_node **node;
 
-	if (tree->inode)
-		btrfs_split_delalloc_extent(tree->inode, orig, split);
+	if (is_inode_io_tree(tree))
+		btrfs_split_delalloc_extent(extent_io_tree_to_inode(tree), orig,
+					    split);
 
 	prealloc->start = orig->start;
 	prealloc->end = split - 1;
@@ -538,8 +575,9 @@ static struct extent_state *clear_state_bit(struct extent_io_tree *tree,
 	u32 bits_to_clear = bits & ~EXTENT_CTLBITS;
 	int ret;
 
-	if (tree->inode)
-		btrfs_clear_delalloc_extent(tree->inode, state, bits);
+	if (is_inode_io_tree(tree))
+		btrfs_clear_delalloc_extent(extent_io_tree_to_inode(tree), state,
+					    bits);
 
 	ret = add_extent_changeset(state, bits_to_clear, changeset, 0);
 	BUG_ON(ret < 0);

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);

fs/btrfs/inode.c

@@ -8511,8 +8511,11 @@ struct inode *btrfs_alloc_inode(struct super_block *sb)
 
 	inode = &ei->vfs_inode;
 	extent_map_tree_init(&ei->extent_tree);
+
+	/* This io tree sets the valid inode. */
 	extent_io_tree_init(fs_info, &ei->io_tree, IO_TREE_INODE_IO);
 	ei->io_tree.inode = ei;
+
 	extent_io_tree_init(fs_info, &ei->file_extent_tree,
 			    IO_TREE_INODE_FILE_EXTENT);
 	/* Lockdep class is set only for the file extent tree. */

fs/btrfs/tests/btrfs-tests.c

@@ -103,7 +103,7 @@ struct btrfs_device *btrfs_alloc_dummy_device(struct btrfs_fs_info *fs_info)
 	if (!dev)
 		return ERR_PTR(-ENOMEM);
 
-	extent_io_tree_init(NULL, &dev->alloc_state, 0);
+	extent_io_tree_init(fs_info, &dev->alloc_state, 0);
 	INIT_LIST_HEAD(&dev->dev_list);
 	list_add(&dev->dev_list, &fs_info->fs_devices->devices);
 

include/trace/events/btrfs.h

@@ -2098,17 +2098,12 @@ TRACE_EVENT(btrfs_set_extent_bit,
 		__field(	unsigned,	set_bits)
 	),
 
-	TP_fast_assign_btrfs(tree->fs_info,
-		__entry->owner = tree->owner;
-		if (tree->inode) {
-			const struct btrfs_inode *inode = tree->inode;
-
-			__entry->ino	= btrfs_ino(inode);
-			__entry->rootid	= inode->root->root_key.objectid;
-		} else {
-			__entry->ino	= 0;
-			__entry->rootid	= 0;
-		}
+	TP_fast_assign_btrfs(extent_io_tree_to_fs_info(tree),
+		const struct btrfs_inode *inode = extent_io_tree_to_inode_const(tree);
+
+		__entry->owner		= tree->owner;
+		__entry->ino		= inode ? btrfs_ino(inode) : 0;
+		__entry->rootid		= inode ? inode->root->root_key.objectid : 0;
 		__entry->start		= start;
 		__entry->len		= len;
 		__entry->set_bits	= set_bits;
@@ -2136,17 +2131,12 @@ TRACE_EVENT(btrfs_clear_extent_bit,
 		__field(	unsigned,	clear_bits)
 	),
 
-	TP_fast_assign_btrfs(tree->fs_info,
-		__entry->owner = tree->owner;
-		if (tree->inode) {
-			const struct btrfs_inode *inode = tree->inode;
+	TP_fast_assign_btrfs(extent_io_tree_to_fs_info(tree),
+		const struct btrfs_inode *inode = extent_io_tree_to_inode_const(tree);
 
-			__entry->ino	= btrfs_ino(inode);
-			__entry->rootid	= inode->root->root_key.objectid;
-		} else {
-			__entry->ino	= 0;
-			__entry->rootid	= 0;
-		}
+		__entry->owner		= tree->owner;
+		__entry->ino		= inode ? btrfs_ino(inode) : 0;
+		__entry->rootid		= inode ? inode->root->root_key.objectid : 0;
 		__entry->start		= start;
 		__entry->len		= len;
 		__entry->clear_bits	= clear_bits;
@@ -2175,17 +2165,12 @@ TRACE_EVENT(btrfs_convert_extent_bit,
 		__field(	unsigned,	clear_bits)
 	),
 
-	TP_fast_assign_btrfs(tree->fs_info,
-		__entry->owner = tree->owner;
-		if (tree->inode) {
-			const struct btrfs_inode *inode = tree->inode;
+	TP_fast_assign_btrfs(extent_io_tree_to_fs_info(tree),
+		const struct btrfs_inode *inode = extent_io_tree_to_inode_const(tree);
 
-			__entry->ino	= btrfs_ino(inode);
-			__entry->rootid	= inode->root->root_key.objectid;
-		} else {
-			__entry->ino	= 0;
-			__entry->rootid	= 0;
-		}
+		__entry->owner		= tree->owner;
+		__entry->ino		= inode ? btrfs_ino(inode) : 0;
+		__entry->rootid		= inode ? inode->root->root_key.objectid : 0;
 		__entry->start		= start;
 		__entry->len		= len;
 		__entry->set_bits	= set_bits;