Btrfs: reduce stack usage in some crucial tree balancing functions

Many of the tree balancing functions follow the same pattern.

1) cow a block
2) do something to the result

This commit breaks them up into two functions so the variables and
code required for part two don't suck down stack during part one.

Signed-off-by: Chris Mason <chris.mason@oracle.com>

fs/btrfs/ctree.c

@@ -2266,66 +2266,27 @@ noinline int btrfs_leaf_free_space(struct btrfs_root *root,
 	return ret;
 }
 
-/*
+static noinline int __push_leaf_right(struct btrfs_trans_handle *trans,
- * push some data in the path leaf to the right, trying to free up at
+				      struct btrfs_root *root,
- * least data_size bytes.  returns zero if the push worked, nonzero otherwise
+				      struct btrfs_path *path,
- *
+				      int data_size, int empty,
- * returns 1 if the push failed because the other node didn't have enough
+				      struct extent_buffer *right,
- * room, 0 if everything worked out and < 0 if there were major errors.
+				      int free_space, u32 left_nritems)
- */
-static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
-			   *root, struct btrfs_path *path, int data_size,
-			   int empty)
 {
 	struct extent_buffer *left = path->nodes[0];
-	struct extent_buffer *right;
+	struct extent_buffer *upper = path->nodes[1];
-	struct extent_buffer *upper;
 	struct btrfs_disk_key disk_key;
 	int slot;
 	u32 i;
-	int free_space;
 	int push_space = 0;
 	int push_items = 0;
 	struct btrfs_item *item;
-	u32 left_nritems;
 	u32 nr;
 	u32 right_nritems;
 	u32 data_end;
 	u32 this_item_size;
 	int ret;
 
-	slot = path->slots[1];
-	if (!path->nodes[1])
-		return 1;
-
-	upper = path->nodes[1];
-	if (slot >= btrfs_header_nritems(upper) - 1)
-		return 1;
-
-	btrfs_assert_tree_locked(path->nodes[1]);
-
-	right = read_node_slot(root, upper, slot + 1);
-	btrfs_tree_lock(right);
-	btrfs_set_lock_blocking(right);
-
-	free_space = btrfs_leaf_free_space(root, right);
-	if (free_space < data_size)
-		goto out_unlock;
-
-	/* cow and double check */
-	ret = btrfs_cow_block(trans, root, right, upper,
-			      slot + 1, &right);
-	if (ret)
-		goto out_unlock;
-
-	free_space = btrfs_leaf_free_space(root, right);
-	if (free_space < data_size)
-		goto out_unlock;
-
-	left_nritems = btrfs_header_nritems(left);
-	if (left_nritems == 0)
-		goto out_unlock;
-
 	if (empty)
 		nr = 0;
 	else
@@ -2334,6 +2295,7 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 	if (path->slots[0] >= left_nritems)
 		push_space += data_size;
 
+	slot = path->slots[1];
 	i = left_nritems - 1;
 	while (i >= nr) {
 		item = btrfs_item_nr(left, i);
@@ -2464,25 +2426,83 @@ static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
 	return 1;
 }
 
+/*
+ * push some data in the path leaf to the right, trying to free up at
+ * least data_size bytes.  returns zero if the push worked, nonzero otherwise
+ *
+ * returns 1 if the push failed because the other node didn't have enough
+ * room, 0 if everything worked out and < 0 if there were major errors.
+ */
+static int push_leaf_right(struct btrfs_trans_handle *trans, struct btrfs_root
+			   *root, struct btrfs_path *path, int data_size,
+			   int empty)
+{
+	struct extent_buffer *left = path->nodes[0];
+	struct extent_buffer *right;
+	struct extent_buffer *upper;
+	int slot;
+	int free_space;
+	u32 left_nritems;
+	int ret;
+
+	if (!path->nodes[1])
+		return 1;
+
+	slot = path->slots[1];
+	upper = path->nodes[1];
+	if (slot >= btrfs_header_nritems(upper) - 1)
+		return 1;
+
+	btrfs_assert_tree_locked(path->nodes[1]);
+
+	right = read_node_slot(root, upper, slot + 1);
+	btrfs_tree_lock(right);
+	btrfs_set_lock_blocking(right);
+
+	free_space = btrfs_leaf_free_space(root, right);
+	if (free_space < data_size)
+		goto out_unlock;
+
+	/* cow and double check */
+	ret = btrfs_cow_block(trans, root, right, upper,
+			      slot + 1, &right);
+	if (ret)
+		goto out_unlock;
+
+	free_space = btrfs_leaf_free_space(root, right);
+	if (free_space < data_size)
+		goto out_unlock;
+
+	left_nritems = btrfs_header_nritems(left);
+	if (left_nritems == 0)
+		goto out_unlock;
+
+	return __push_leaf_right(trans, root, path, data_size, empty,
+				right, free_space, left_nritems);
+out_unlock:
+	btrfs_tree_unlock(right);
+	free_extent_buffer(right);
+	return 1;
+}
+
 /*
  * push some data in the path leaf to the left, trying to free up at
  * least data_size bytes.  returns zero if the push worked, nonzero otherwise
  */
-static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
+static noinline int __push_leaf_left(struct btrfs_trans_handle *trans,
-			  *root, struct btrfs_path *path, int data_size,
+				     struct btrfs_root *root,
-			  int empty)
+				     struct btrfs_path *path, int data_size,
+				     int empty, struct extent_buffer *left,
+				     int free_space, int right_nritems)
 {
 	struct btrfs_disk_key disk_key;
 	struct extent_buffer *right = path->nodes[0];
-	struct extent_buffer *left;
 	int slot;
 	int i;
-	int free_space;
 	int push_space = 0;
 	int push_items = 0;
 	struct btrfs_item *item;
 	u32 old_left_nritems;
-	u32 right_nritems;
 	u32 nr;
 	int ret = 0;
 	int wret;
@@ -2490,41 +2510,6 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	u32 old_left_item_size;
 
 	slot = path->slots[1];
-	if (slot == 0)
-		return 1;
-	if (!path->nodes[1])
-		return 1;
-
-	right_nritems = btrfs_header_nritems(right);
-	if (right_nritems == 0)
-		return 1;
-
-	btrfs_assert_tree_locked(path->nodes[1]);
-
-	left = read_node_slot(root, path->nodes[1], slot - 1);
-	btrfs_tree_lock(left);
-	btrfs_set_lock_blocking(left);
-
-	free_space = btrfs_leaf_free_space(root, left);
-	if (free_space < data_size) {
-		ret = 1;
-		goto out;
-	}
-
-	/* cow and double check */
-	ret = btrfs_cow_block(trans, root, left,
-			      path->nodes[1], slot - 1, &left);
-	if (ret) {
-		/* we hit -ENOSPC, but it isn't fatal here */
-		ret = 1;
-		goto out;
-	}
-
-	free_space = btrfs_leaf_free_space(root, left);
-	if (free_space < data_size) {
-		ret = 1;
-		goto out;
-	}
 
 	if (empty)
 		nr = right_nritems;
@@ -2691,146 +2676,86 @@ static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
 	return ret;
 }
 
+/*
+ * push some data in the path leaf to the left, trying to free up at
+ * least data_size bytes.  returns zero if the push worked, nonzero otherwise
+ */
+static int push_leaf_left(struct btrfs_trans_handle *trans, struct btrfs_root
+			  *root, struct btrfs_path *path, int data_size,
+			  int empty)
+{
+	struct extent_buffer *right = path->nodes[0];
+	struct extent_buffer *left;
+	int slot;
+	int free_space;
+	u32 right_nritems;
+	int ret = 0;
+
+	slot = path->slots[1];
+	if (slot == 0)
+		return 1;
+	if (!path->nodes[1])
+		return 1;
+
+	right_nritems = btrfs_header_nritems(right);
+	if (right_nritems == 0)
+		return 1;
+
+	btrfs_assert_tree_locked(path->nodes[1]);
+
+	left = read_node_slot(root, path->nodes[1], slot - 1);
+	btrfs_tree_lock(left);
+	btrfs_set_lock_blocking(left);
+
+	free_space = btrfs_leaf_free_space(root, left);
+	if (free_space < data_size) {
+		ret = 1;
+		goto out;
+	}
+
+	/* cow and double check */
+	ret = btrfs_cow_block(trans, root, left,
+			      path->nodes[1], slot - 1, &left);
+	if (ret) {
+		/* we hit -ENOSPC, but it isn't fatal here */
+		ret = 1;
+		goto out;
+	}
+
+	free_space = btrfs_leaf_free_space(root, left);
+	if (free_space < data_size) {
+		ret = 1;
+		goto out;
+	}
+
+	return __push_leaf_left(trans, root, path, data_size,
+			       empty, left, free_space, right_nritems);
+out:
+	btrfs_tree_unlock(left);
+	free_extent_buffer(left);
+	return ret;
+}
+
 /*
  * split the path's leaf in two, making sure there is at least data_size
  * available for the resulting leaf level of the path.
  *
  * returns 0 if all went well and < 0 on failure.
  */
-static noinline int split_leaf(struct btrfs_trans_handle *trans,
+static noinline int copy_for_split(struct btrfs_trans_handle *trans,
 			       struct btrfs_root *root,
-			       struct btrfs_key *ins_key,
+			       struct btrfs_path *path,
-			       struct btrfs_path *path, int data_size,
+			       struct extent_buffer *l,
-			       int extend)
+			       struct extent_buffer *right,
+			       int slot, int mid, int nritems)
 {
-	struct extent_buffer *l;
-	u32 nritems;
-	int mid;
-	int slot;
-	struct extent_buffer *right;
 	int data_copy_size;
 	int rt_data_off;
 	int i;
 	int ret = 0;
 	int wret;
-	int double_split;
-	int num_doubles = 0;
 	struct btrfs_disk_key disk_key;
 
-	/* first try to make some room by pushing left and right */
-	if (data_size && ins_key->type != BTRFS_DIR_ITEM_KEY) {
-		wret = push_leaf_right(trans, root, path, data_size, 0);
-		if (wret < 0)
-			return wret;
-		if (wret) {
-			wret = push_leaf_left(trans, root, path, data_size, 0);
-			if (wret < 0)
-				return wret;
-		}
-		l = path->nodes[0];
-
-		/* did the pushes work? */
-		if (btrfs_leaf_free_space(root, l) >= data_size)
-			return 0;
-	}
-
-	if (!path->nodes[1]) {
-		ret = insert_new_root(trans, root, path, 1);
-		if (ret)
-			return ret;
-	}
-again:
-	double_split = 0;
-	l = path->nodes[0];
-	slot = path->slots[0];
-	nritems = btrfs_header_nritems(l);
-	mid = (nritems + 1) / 2;
-
-	right = btrfs_alloc_free_block(trans, root, root->leafsize,
-					path->nodes[1]->start,
-					root->root_key.objectid,
-					trans->transid, 0, l->start, 0);
-	if (IS_ERR(right)) {
-		BUG_ON(1);
-		return PTR_ERR(right);
-	}
-
-	memset_extent_buffer(right, 0, 0, sizeof(struct btrfs_header));
-	btrfs_set_header_bytenr(right, right->start);
-	btrfs_set_header_generation(right, trans->transid);
-	btrfs_set_header_owner(right, root->root_key.objectid);
-	btrfs_set_header_level(right, 0);
-	write_extent_buffer(right, root->fs_info->fsid,
-			    (unsigned long)btrfs_header_fsid(right),
-			    BTRFS_FSID_SIZE);
-
-	write_extent_buffer(right, root->fs_info->chunk_tree_uuid,
-			    (unsigned long)btrfs_header_chunk_tree_uuid(right),
-			    BTRFS_UUID_SIZE);
-	if (mid <= slot) {
-		if (nritems == 1 ||
-		    leaf_space_used(l, mid, nritems - mid) + data_size >
-			BTRFS_LEAF_DATA_SIZE(root)) {
-			if (slot >= nritems) {
-				btrfs_cpu_key_to_disk(&disk_key, ins_key);
-				btrfs_set_header_nritems(right, 0);
-				wret = insert_ptr(trans, root, path,
-						  &disk_key, right->start,
-						  path->slots[1] + 1, 1);
-				if (wret)
-					ret = wret;
-
-				btrfs_tree_unlock(path->nodes[0]);
-				free_extent_buffer(path->nodes[0]);
-				path->nodes[0] = right;
-				path->slots[0] = 0;
-				path->slots[1] += 1;
-				btrfs_mark_buffer_dirty(right);
-				return ret;
-			}
-			mid = slot;
-			if (mid != nritems &&
-			    leaf_space_used(l, mid, nritems - mid) +
-			    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
-				double_split = 1;
-			}
-		}
-	} else {
-		if (leaf_space_used(l, 0, mid) + data_size >
-			BTRFS_LEAF_DATA_SIZE(root)) {
-			if (!extend && data_size && slot == 0) {
-				btrfs_cpu_key_to_disk(&disk_key, ins_key);
-				btrfs_set_header_nritems(right, 0);
-				wret = insert_ptr(trans, root, path,
-						  &disk_key,
-						  right->start,
-						  path->slots[1], 1);
-				if (wret)
-					ret = wret;
-				btrfs_tree_unlock(path->nodes[0]);
-				free_extent_buffer(path->nodes[0]);
-				path->nodes[0] = right;
-				path->slots[0] = 0;
-				if (path->slots[1] == 0) {
-					wret = fixup_low_keys(trans, root,
-						      path, &disk_key, 1);
-					if (wret)
-						ret = wret;
-				}
-				btrfs_mark_buffer_dirty(right);
-				return ret;
-			} else if ((extend || !data_size) && slot == 0) {
-				mid = 1;
-			} else {
-				mid = slot;
-				if (mid != nritems &&
-				    leaf_space_used(l, mid, nritems - mid) +
-				    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
-					double_split = 1;
-				}
-			}
-		}
-	}
 	nritems = nritems - mid;
 	btrfs_set_header_nritems(right, nritems);
 	data_copy_size = btrfs_item_end_nr(l, mid) - leaf_data_end(root, l);
@@ -2896,11 +2821,160 @@ static noinline int split_leaf(struct btrfs_trans_handle *trans,
 
 	BUG_ON(path->slots[0] < 0);
 
+	return ret;
+}
+
+/*
+ * split the path's leaf in two, making sure there is at least data_size
+ * available for the resulting leaf level of the path.
+ *
+ * returns 0 if all went well and < 0 on failure.
+ */
+static noinline int split_leaf(struct btrfs_trans_handle *trans,
+			       struct btrfs_root *root,
+			       struct btrfs_key *ins_key,
+			       struct btrfs_path *path, int data_size,
+			       int extend)
+{
+	struct extent_buffer *l;
+	u32 nritems;
+	int mid;
+	int slot;
+	struct extent_buffer *right;
+	int ret = 0;
+	int wret;
+	int double_split;
+	int num_doubles = 0;
+
+	/* first try to make some room by pushing left and right */
+	if (data_size && ins_key->type != BTRFS_DIR_ITEM_KEY) {
+		wret = push_leaf_right(trans, root, path, data_size, 0);
+		if (wret < 0)
+			return wret;
+		if (wret) {
+			wret = push_leaf_left(trans, root, path, data_size, 0);
+			if (wret < 0)
+				return wret;
+		}
+		l = path->nodes[0];
+
+		/* did the pushes work? */
+		if (btrfs_leaf_free_space(root, l) >= data_size)
+			return 0;
+	}
+
+	if (!path->nodes[1]) {
+		ret = insert_new_root(trans, root, path, 1);
+		if (ret)
+			return ret;
+	}
+again:
+	double_split = 0;
+	l = path->nodes[0];
+	slot = path->slots[0];
+	nritems = btrfs_header_nritems(l);
+	mid = (nritems + 1) / 2;
+
+	right = btrfs_alloc_free_block(trans, root, root->leafsize,
+					path->nodes[1]->start,
+					root->root_key.objectid,
+					trans->transid, 0, l->start, 0);
+	if (IS_ERR(right)) {
+		BUG_ON(1);
+		return PTR_ERR(right);
+	}
+
+	memset_extent_buffer(right, 0, 0, sizeof(struct btrfs_header));
+	btrfs_set_header_bytenr(right, right->start);
+	btrfs_set_header_generation(right, trans->transid);
+	btrfs_set_header_owner(right, root->root_key.objectid);
+	btrfs_set_header_level(right, 0);
+	write_extent_buffer(right, root->fs_info->fsid,
+			    (unsigned long)btrfs_header_fsid(right),
+			    BTRFS_FSID_SIZE);
+
+	write_extent_buffer(right, root->fs_info->chunk_tree_uuid,
+			    (unsigned long)btrfs_header_chunk_tree_uuid(right),
+			    BTRFS_UUID_SIZE);
+
+	if (mid <= slot) {
+		if (nritems == 1 ||
+		    leaf_space_used(l, mid, nritems - mid) + data_size >
+			BTRFS_LEAF_DATA_SIZE(root)) {
+			if (slot >= nritems) {
+				struct btrfs_disk_key disk_key;
+
+				btrfs_cpu_key_to_disk(&disk_key, ins_key);
+				btrfs_set_header_nritems(right, 0);
+				wret = insert_ptr(trans, root, path,
+						  &disk_key, right->start,
+						  path->slots[1] + 1, 1);
+				if (wret)
+					ret = wret;
+
+				btrfs_tree_unlock(path->nodes[0]);
+				free_extent_buffer(path->nodes[0]);
+				path->nodes[0] = right;
+				path->slots[0] = 0;
+				path->slots[1] += 1;
+				btrfs_mark_buffer_dirty(right);
+				return ret;
+			}
+			mid = slot;
+			if (mid != nritems &&
+			    leaf_space_used(l, mid, nritems - mid) +
+			    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
+				double_split = 1;
+			}
+		}
+	} else {
+		if (leaf_space_used(l, 0, mid) + data_size >
+			BTRFS_LEAF_DATA_SIZE(root)) {
+			if (!extend && data_size && slot == 0) {
+				struct btrfs_disk_key disk_key;
+
+				btrfs_cpu_key_to_disk(&disk_key, ins_key);
+				btrfs_set_header_nritems(right, 0);
+				wret = insert_ptr(trans, root, path,
+						  &disk_key,
+						  right->start,
+						  path->slots[1], 1);
+				if (wret)
+					ret = wret;
+				btrfs_tree_unlock(path->nodes[0]);
+				free_extent_buffer(path->nodes[0]);
+				path->nodes[0] = right;
+				path->slots[0] = 0;
+				if (path->slots[1] == 0) {
+					wret = fixup_low_keys(trans, root,
+						      path, &disk_key, 1);
+					if (wret)
+						ret = wret;
+				}
+				btrfs_mark_buffer_dirty(right);
+				return ret;
+			} else if ((extend || !data_size) && slot == 0) {
+				mid = 1;
+			} else {
+				mid = slot;
+				if (mid != nritems &&
+				    leaf_space_used(l, mid, nritems - mid) +
+				    data_size > BTRFS_LEAF_DATA_SIZE(root)) {
+					double_split = 1;
+				}
+			}
+		}
+	}
+
+	ret = copy_for_split(trans, root, path, l, right, slot, mid, nritems);
+	BUG_ON(ret);
+
 	if (double_split) {
 		BUG_ON(num_doubles != 0);
 		num_doubles++;
 		goto again;
 	}
+
 	return ret;
 }
 
@@ -3382,39 +3456,27 @@ int btrfs_insert_some_items(struct btrfs_trans_handle *trans,
 }
 
 /*
- * Given a key and some data, insert items into the tree.
+ * this is a helper for btrfs_insert_empty_items, the main goal here is
- * This does all the path init required, making room in the tree if needed.
+ * to save stack depth by doing the bulk of the work in a function
+ * that doesn't call btrfs_search_slot
  */
-int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
+static noinline_for_stack int
-			    struct btrfs_root *root,
+setup_items_for_insert(struct btrfs_trans_handle *trans,
-			    struct btrfs_path *path,
+		      struct btrfs_root *root, struct btrfs_path *path,
-			    struct btrfs_key *cpu_key, u32 *data_size,
+		      struct btrfs_key *cpu_key, u32 *data_size,
-			    int nr)
+		      u32 total_data, u32 total_size, int nr)
 {
-	struct extent_buffer *leaf;
 	struct btrfs_item *item;
-	int ret = 0;
-	int slot;
-	int slot_orig;
 	int i;
 	u32 nritems;
-	u32 total_size = 0;
-	u32 total_data = 0;
 	unsigned int data_end;
 	struct btrfs_disk_key disk_key;
+	int ret;
+	struct extent_buffer *leaf;
+	int slot;
 
-	for (i = 0; i < nr; i++)
-		total_data += data_size[i];
-
-	total_size = total_data + (nr * sizeof(struct btrfs_item));
-	ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
-	if (ret == 0)
-		return -EEXIST;
-	if (ret < 0)
-		goto out;
-
-	slot_orig = path->slots[0];
 	leaf = path->nodes[0];
+	slot = path->slots[0];
 
 	nritems = btrfs_header_nritems(leaf);
 	data_end = leaf_data_end(root, leaf);
@@ -3426,9 +3488,6 @@ int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
 		BUG();
 	}
 
-	slot = path->slots[0];
-	BUG_ON(slot < 0);
-
 	if (slot != nritems) {
 		unsigned int old_data = btrfs_item_end_nr(leaf, slot);
 
@@ -3484,11 +3543,13 @@ int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
 		data_end -= data_size[i];
 		btrfs_set_item_size(leaf, item, data_size[i]);
 	}
+
 	btrfs_set_header_nritems(leaf, nritems + nr);
 	btrfs_mark_buffer_dirty(leaf);
 
 	ret = 0;
 	if (slot == 0) {
+		struct btrfs_disk_key disk_key;
 		btrfs_cpu_key_to_disk(&disk_key, cpu_key);
 		ret = fixup_low_keys(trans, root, path, &disk_key, 1);
 	}
@@ -3497,6 +3558,43 @@ int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
 		btrfs_print_leaf(root, leaf);
 		BUG();
 	}
+	return ret;
+}
+
+/*
+ * Given a key and some data, insert items into the tree.
+ * This does all the path init required, making room in the tree if needed.
+ */
+int btrfs_insert_empty_items(struct btrfs_trans_handle *trans,
+			    struct btrfs_root *root,
+			    struct btrfs_path *path,
+			    struct btrfs_key *cpu_key, u32 *data_size,
+			    int nr)
+{
+	struct extent_buffer *leaf;
+	int ret = 0;
+	int slot;
+	int i;
+	u32 total_size = 0;
+	u32 total_data = 0;
+
+	for (i = 0; i < nr; i++)
+		total_data += data_size[i];
+
+	total_size = total_data + (nr * sizeof(struct btrfs_item));
+	ret = btrfs_search_slot(trans, root, cpu_key, path, total_size, 1);
+	if (ret == 0)
+		return -EEXIST;
+	if (ret < 0)
+		goto out;
+
+	leaf = path->nodes[0];
+	slot = path->slots[0];
+	BUG_ON(slot < 0);
+
+	ret = setup_items_for_insert(trans, root, path, cpu_key, data_size,
+			       total_data, total_size, nr);
+
 out:
 	btrfs_unlock_up_safe(path, 1);
 	return ret;