text: // SPDX-License-Identifier: GPL-2.0
  /*
   * Copyright (C) 2009 Oracle.  All rights reserved.
   */
  
  #include <linux/sched.h>
  #include <linux/slab.h>
  #include <linux/sort.h>
  #include "ctree.h"
  #include "delayed-ref.h"
  #include "transaction.h"
  #include "qgroup.h"
  #include "space-info.h"
  #include "tree-mod-log.h"
  
  struct kmem_cache *btrfs_delayed_ref_head_cachep;
  struct kmem_cache *btrfs_delayed_tree_ref_cachep;
  struct kmem_cache *btrfs_delayed_data_ref_cachep;
  struct kmem_cache *btrfs_delayed_extent_op_cachep;
  /*
   * delayed back reference update tracking.  For subvolume trees
   * we queue up extent allocations and backref maintenance for
   * delayed processing.   This avoids deep call chains where we
   * add extents in the middle of btrfs_search_slot, and it allows
   * us to buffer up frequently modified backrefs in an rb tree instead
   * of hammering updates on the extent allocation tree.
   */
  
  bool btrfs_check_space_for_delayed_refs(struct btrfs_fs_info *fs_info)
  {
  	struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
  	struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
  	bool ret = false;
  	u64 reserved;
  
  	spin_lock(&global_rsv->lock);
  	reserved = global_rsv->reserved;
  	spin_unlock(&global_rsv->lock);
  
  	/*
  	 * Since the global reserve is just kind of magic we don't really want
  	 * to rely on it to save our bacon, so if our size is more than the
  	 * delayed_refs_rsv and the global rsv then it's time to think about
  	 * bailing.
  	 */
  	spin_lock(&delayed_refs_rsv->lock);
  	reserved += delayed_refs_rsv->reserved;
  	if (delayed_refs_rsv->size >= reserved)
  		ret = true;
  	spin_unlock(&delayed_refs_rsv->lock);
  	return ret;
  }
  
  int btrfs_should_throttle_delayed_refs(struct btrfs_trans_handle *trans)
  {
  	u64 num_entries =
  		atomic_read(&trans->transaction->delayed_refs.num_entries);
  	u64 avg_runtime;
  	u64 val;
  
  	smp_mb();
  	avg_runtime = trans->fs_info->avg_delayed_ref_runtime;
  	val = num_entries * avg_runtime;
  	if (val >= NSEC_PER_SEC)
  		return 1;
  	if (val >= NSEC_PER_SEC / 2)
  		return 2;
  
  	return btrfs_check_space_for_delayed_refs(trans->fs_info);
  }
  
  /**
   * Release a ref head's reservation
   *
   * @fs_info:  the filesystem
   * @nr:       number of items to drop
   *
   * This drops the delayed ref head's count from the delayed refs rsv and frees
   * any excess reservation we had.
   */
  void btrfs_delayed_refs_rsv_release(struct btrfs_fs_info *fs_info, int nr)
  {
  	struct btrfs_block_rsv *block_rsv = &fs_info->delayed_refs_rsv;
  	u64 num_bytes = btrfs_calc_insert_metadata_size(fs_info, nr);
  	u64 released = 0;
  
  	released = btrfs_block_rsv_release(fs_info, block_rsv, num_bytes, NULL);
  	if (released)
  		trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",
  					      0, released, 0);
  }
  
  /*
   * btrfs_update_delayed_refs_rsv - adjust the size of the delayed refs rsv
   * @trans - the trans that may have generated delayed refs
   *
   * This is to be called anytime we may have adjusted trans->delayed_ref_updates,
   * it'll calculate the additional size and add it to the delayed_refs_rsv.
   */
  void btrfs_update_delayed_refs_rsv(struct btrfs_trans_handle *trans)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv;
  	u64 num_bytes;
  
  	if (!trans->delayed_ref_updates)
  		return;
  
  	num_bytes = btrfs_calc_insert_metadata_size(fs_info,
  						    trans->delayed_ref_updates);
  	spin_lock(&delayed_rsv->lock);
  	delayed_rsv->size += num_bytes;
  	delayed_rsv->full = 0;
  	spin_unlock(&delayed_rsv->lock);
  	trans->delayed_ref_updates = 0;
  }
  
  /**
   * Transfer bytes to our delayed refs rsv
   *
   * @fs_info:   the filesystem
   * @src:       source block rsv to transfer from
   * @num_bytes: number of bytes to transfer
   *
   * This transfers up to the num_bytes amount from the src rsv to the
   * delayed_refs_rsv.  Any extra bytes are returned to the space info.
   */
  void btrfs_migrate_to_delayed_refs_rsv(struct btrfs_fs_info *fs_info,
  				       struct btrfs_block_rsv *src,
  				       u64 num_bytes)
  {
  	struct btrfs_block_rsv *delayed_refs_rsv = &fs_info->delayed_refs_rsv;
  	u64 to_free = 0;
  
  	spin_lock(&src->lock);
  	src->reserved -= num_bytes;
  	src->size -= num_bytes;
  	spin_unlock(&src->lock);
  
  	spin_lock(&delayed_refs_rsv->lock);
  	if (delayed_refs_rsv->size > delayed_refs_rsv->reserved) {
  		u64 delta = delayed_refs_rsv->size -
  			delayed_refs_rsv->reserved;
  		if (num_bytes > delta) {
  			to_free = num_bytes - delta;
  			num_bytes = delta;
  		}
  	} else {
  		to_free = num_bytes;
  		num_bytes = 0;
  	}
  
  	if (num_bytes)
  		delayed_refs_rsv->reserved += num_bytes;
  	if (delayed_refs_rsv->reserved >= delayed_refs_rsv->size)
  		delayed_refs_rsv->full = 1;
  	spin_unlock(&delayed_refs_rsv->lock);
  
  	if (num_bytes)
  		trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",
  					      0, num_bytes, 1);
  	if (to_free)
  		btrfs_space_info_free_bytes_may_use(fs_info,
  				delayed_refs_rsv->space_info, to_free);
  }
  
  /**
   * Refill based on our delayed refs usage
   *
   * @fs_info: the filesystem
   * @flush:   control how we can flush for this reservation.
   *
   * This will refill the delayed block_rsv up to 1 items size worth of space and
   * will return -ENOSPC if we can't make the reservation.
   */
  int btrfs_delayed_refs_rsv_refill(struct btrfs_fs_info *fs_info,
  				  enum btrfs_reserve_flush_enum flush)
  {
  	struct btrfs_block_rsv *block_rsv = &fs_info->delayed_refs_rsv;
  	u64 limit = btrfs_calc_insert_metadata_size(fs_info, 1);
  	u64 num_bytes = 0;
  	int ret = -ENOSPC;
  
  	spin_lock(&block_rsv->lock);
  	if (block_rsv->reserved < block_rsv->size) {
  		num_bytes = block_rsv->size - block_rsv->reserved;
  		num_bytes = min(num_bytes, limit);
  	}
  	spin_unlock(&block_rsv->lock);
  
  	if (!num_bytes)
  		return 0;
  
  	ret = btrfs_reserve_metadata_bytes(fs_info->extent_root, block_rsv,
  					   num_bytes, flush);
  	if (ret)
  		return ret;
  	btrfs_block_rsv_add_bytes(block_rsv, num_bytes, 0);
  	trace_btrfs_space_reservation(fs_info, "delayed_refs_rsv",
  				      0, num_bytes, 1);
  	return 0;
  }
  
  /*
   * compare two delayed tree backrefs with same bytenr and type
   */
  static int comp_tree_refs(struct btrfs_delayed_tree_ref *ref1,
  			  struct btrfs_delayed_tree_ref *ref2)
  {
  	if (ref1->node.type == BTRFS_TREE_BLOCK_REF_KEY) {
  		if (ref1->root < ref2->root)
  			return -1;
  		if (ref1->root > ref2->root)
  			return 1;
  	} else {
  		if (ref1->parent < ref2->parent)
  			return -1;
  		if (ref1->parent > ref2->parent)
  			return 1;
  	}
  	return 0;
  }
  
  /*
   * compare two delayed data backrefs with same bytenr and type
   */
  static int comp_data_refs(struct btrfs_delayed_data_ref *ref1,
  			  struct btrfs_delayed_data_ref *ref2)
  {
  	if (ref1->node.type == BTRFS_EXTENT_DATA_REF_KEY) {
  		if (ref1->root < ref2->root)
  			return -1;
  		if (ref1->root > ref2->root)
  			return 1;
  		if (ref1->objectid < ref2->objectid)
  			return -1;
  		if (ref1->objectid > ref2->objectid)
  			return 1;
  		if (ref1->offset < ref2->offset)
  			return -1;
  		if (ref1->offset > ref2->offset)
  			return 1;
  	} else {
  		if (ref1->parent < ref2->parent)
  			return -1;
  		if (ref1->parent > ref2->parent)
  			return 1;
  	}
  	return 0;
  }
  
  static int comp_refs(struct btrfs_delayed_ref_node *ref1,
  		     struct btrfs_delayed_ref_node *ref2,
  		     bool check_seq)
  {
  	int ret = 0;
  
  	if (ref1->type < ref2->type)
  		return -1;
  	if (ref1->type > ref2->type)
  		return 1;
  	if (ref1->type == BTRFS_TREE_BLOCK_REF_KEY ||
  	    ref1->type == BTRFS_SHARED_BLOCK_REF_KEY)
  		ret = comp_tree_refs(btrfs_delayed_node_to_tree_ref(ref1),
  				     btrfs_delayed_node_to_tree_ref(ref2));
  	else
  		ret = comp_data_refs(btrfs_delayed_node_to_data_ref(ref1),
  				     btrfs_delayed_node_to_data_ref(ref2));
  	if (ret)
  		return ret;
  	if (check_seq) {
  		if (ref1->seq < ref2->seq)
  			return -1;
  		if (ref1->seq > ref2->seq)
  			return 1;
  	}
  	return 0;
  }
  
  /* insert a new ref to head ref rbtree */
  static struct btrfs_delayed_ref_head *htree_insert(struct rb_root_cached *root,
  						   struct rb_node *node)
  {
  	struct rb_node **p = &root->rb_root.rb_node;
  	struct rb_node *parent_node = NULL;
  	struct btrfs_delayed_ref_head *entry;
  	struct btrfs_delayed_ref_head *ins;
  	u64 bytenr;
  	bool leftmost = true;
  
  	ins = rb_entry(node, struct btrfs_delayed_ref_head, href_node);
  	bytenr = ins->bytenr;
  	while (*p) {
  		parent_node = *p;
  		entry = rb_entry(parent_node, struct btrfs_delayed_ref_head,
  				 href_node);
  
  		if (bytenr < entry->bytenr) {
  			p = &(*p)->rb_left;
  		} else if (bytenr > entry->bytenr) {
  			p = &(*p)->rb_right;
  			leftmost = false;
  		} else {
  			return entry;
  		}
  	}
  
  	rb_link_node(node, parent_node, p);
  	rb_insert_color_cached(node, root, leftmost);
  	return NULL;
  }
  
  static struct btrfs_delayed_ref_node* tree_insert(struct rb_root_cached *root,
  		struct btrfs_delayed_ref_node *ins)
  {
  	struct rb_node **p = &root->rb_root.rb_node;
  	struct rb_node *node = &ins->ref_node;
  	struct rb_node *parent_node = NULL;
  	struct btrfs_delayed_ref_node *entry;
  	bool leftmost = true;
  
  	while (*p) {
  		int comp;
  
  		parent_node = *p;
  		entry = rb_entry(parent_node, struct btrfs_delayed_ref_node,
  				 ref_node);
  		comp = comp_refs(ins, entry, true);
  		if (comp < 0) {
  			p = &(*p)->rb_left;
  		} else if (comp > 0) {
  			p = &(*p)->rb_right;
  			leftmost = false;
  		} else {
  			return entry;
  		}
  	}
  
  	rb_link_node(node, parent_node, p);
  	rb_insert_color_cached(node, root, leftmost);
  	return NULL;
  }
  
  static struct btrfs_delayed_ref_head *find_first_ref_head(
  		struct btrfs_delayed_ref_root *dr)
  {
  	struct rb_node *n;
  	struct btrfs_delayed_ref_head *entry;
  
  	n = rb_first_cached(&dr->href_root);
  	if (!n)
  		return NULL;
  
  	entry = rb_entry(n, struct btrfs_delayed_ref_head, href_node);
  
  	return entry;
  }
  
  /*
   * Find a head entry based on bytenr. This returns the delayed ref head if it
   * was able to find one, or NULL if nothing was in that spot.  If return_bigger
   * is given, the next bigger entry is returned if no exact match is found.
   */
  static struct btrfs_delayed_ref_head *find_ref_head(
  		struct btrfs_delayed_ref_root *dr, u64 bytenr,
  		bool return_bigger)
  {
  	struct rb_root *root = &dr->href_root.rb_root;
  	struct rb_node *n;
  	struct btrfs_delayed_ref_head *entry;
  
  	n = root->rb_node;
  	entry = NULL;
  	while (n) {
  		entry = rb_entry(n, struct btrfs_delayed_ref_head, href_node);
  
  		if (bytenr < entry->bytenr)
  			n = n->rb_left;
  		else if (bytenr > entry->bytenr)
  			n = n->rb_right;
  		else
  			return entry;
  	}
  	if (entry && return_bigger) {
  		if (bytenr > entry->bytenr) {
  			n = rb_next(&entry->href_node);
  			if (!n)
  				return NULL;
  			entry = rb_entry(n, struct btrfs_delayed_ref_head,
  					 href_node);
  		}
  		return entry;
  	}
  	return NULL;
  }
  
  int btrfs_delayed_ref_lock(struct btrfs_delayed_ref_root *delayed_refs,
  			   struct btrfs_delayed_ref_head *head)
  {
  	lockdep_assert_held(&delayed_refs->lock);
  	if (mutex_trylock(&head->mutex))
  		return 0;
  
  	refcount_inc(&head->refs);
  	spin_unlock(&delayed_refs->lock);
  
  	mutex_lock(&head->mutex);
  	spin_lock(&delayed_refs->lock);
  	if (RB_EMPTY_NODE(&head->href_node)) {
  		mutex_unlock(&head->mutex);
  		btrfs_put_delayed_ref_head(head);
  		return -EAGAIN;
  	}
  	btrfs_put_delayed_ref_head(head);
  	return 0;
  }
  
  static inline void drop_delayed_ref(struct btrfs_trans_handle *trans,
  				    struct btrfs_delayed_ref_root *delayed_refs,
  				    struct btrfs_delayed_ref_head *head,
  				    struct btrfs_delayed_ref_node *ref)
  {
  	lockdep_assert_held(&head->lock);
  	rb_erase_cached(&ref->ref_node, &head->ref_tree);
  	RB_CLEAR_NODE(&ref->ref_node);
  	if (!list_empty(&ref->add_list))
  		list_del(&ref->add_list);
  	ref->in_tree = 0;
  	btrfs_put_delayed_ref(ref);
  	atomic_dec(&delayed_refs->num_entries);
  }
  
  static bool merge_ref(struct btrfs_trans_handle *trans,
  		      struct btrfs_delayed_ref_root *delayed_refs,
  		      struct btrfs_delayed_ref_head *head,
  		      struct btrfs_delayed_ref_node *ref,
  		      u64 seq)
  {
  	struct btrfs_delayed_ref_node *next;
  	struct rb_node *node = rb_next(&ref->ref_node);
  	bool done = false;
  
  	while (!done && node) {
  		int mod;
  
  		next = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
  		node = rb_next(node);
  		if (seq && next->seq >= seq)
  			break;
  		if (comp_refs(ref, next, false))
  			break;
  
  		if (ref->action == next->action) {
  			mod = next->ref_mod;
  		} else {
  			if (ref->ref_mod < next->ref_mod) {
  				swap(ref, next);
  				done = true;
  			}
  			mod = -next->ref_mod;
  		}
  
  		drop_delayed_ref(trans, delayed_refs, head, next);
  		ref->ref_mod += mod;
  		if (ref->ref_mod == 0) {
  			drop_delayed_ref(trans, delayed_refs, head, ref);
  			done = true;
  		} else {
  			/*
  			 * Can't have multiples of the same ref on a tree block.
  			 */
  			WARN_ON(ref->type == BTRFS_TREE_BLOCK_REF_KEY ||
  				ref->type == BTRFS_SHARED_BLOCK_REF_KEY);
  		}
  	}
  
  	return done;
  }
  
  void btrfs_merge_delayed_refs(struct btrfs_trans_handle *trans,
  			      struct btrfs_delayed_ref_root *delayed_refs,
  			      struct btrfs_delayed_ref_head *head)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_delayed_ref_node *ref;
  	struct rb_node *node;
  	u64 seq = 0;
  
  	lockdep_assert_held(&head->lock);
  
  	if (RB_EMPTY_ROOT(&head->ref_tree.rb_root))
  		return;
  
  	/* We don't have too many refs to merge for data. */
  	if (head->is_data)
  		return;
  
  	seq = btrfs_tree_mod_log_lowest_seq(fs_info);
  again:
  	for (node = rb_first_cached(&head->ref_tree); node;
  	     node = rb_next(node)) {
  		ref = rb_entry(node, struct btrfs_delayed_ref_node, ref_node);
  		if (seq && ref->seq >= seq)
  			continue;
  		if (merge_ref(trans, delayed_refs, head, ref, seq))
  			goto again;
  	}
  }
  
  int btrfs_check_delayed_seq(struct btrfs_fs_info *fs_info, u64 seq)
  {
  	int ret = 0;
  	u64 min_seq = btrfs_tree_mod_log_lowest_seq(fs_info);
  
  	if (min_seq != 0 && seq >= min_seq) {
  		btrfs_debug(fs_info,
  			    "holding back delayed_ref %llu, lowest is %llu",
  			    seq, min_seq);
  		ret = 1;
  	}
  
  	return ret;
  }
  
  struct btrfs_delayed_ref_head *btrfs_select_ref_head(
  		struct btrfs_delayed_ref_root *delayed_refs)
  {
  	struct btrfs_delayed_ref_head *head;
  
  again:
  	head = find_ref_head(delayed_refs, delayed_refs->run_delayed_start,
  			     true);
  	if (!head && delayed_refs->run_delayed_start != 0) {
  		delayed_refs->run_delayed_start = 0;
  		head = find_first_ref_head(delayed_refs);
  	}
  	if (!head)
  		return NULL;
  
  	while (head->processing) {
  		struct rb_node *node;
  
  		node = rb_next(&head->href_node);
  		if (!node) {
  			if (delayed_refs->run_delayed_start == 0)
  				return NULL;
  			delayed_refs->run_delayed_start = 0;
  			goto again;
  		}
  		head = rb_entry(node, struct btrfs_delayed_ref_head,
  				href_node);
  	}
  
  	head->processing = 1;
  	WARN_ON(delayed_refs->num_heads_ready == 0);
  	delayed_refs->num_heads_ready--;
  	delayed_refs->run_delayed_start = head->bytenr +
  		head->num_bytes;
  	return head;
  }
  
  void btrfs_delete_ref_head(struct btrfs_delayed_ref_root *delayed_refs,
  			   struct btrfs_delayed_ref_head *head)
  {
  	lockdep_assert_held(&delayed_refs->lock);
  	lockdep_assert_held(&head->lock);
  
  	rb_erase_cached(&head->href_node, &delayed_refs->href_root);
  	RB_CLEAR_NODE(&head->href_node);
  	atomic_dec(&delayed_refs->num_entries);
  	delayed_refs->num_heads--;
  	if (head->processing == 0)
  		delayed_refs->num_heads_ready--;
  }
  
  /*
   * Helper to insert the ref_node to the tail or merge with tail.
   *
   * Return 0 for insert.
   * Return >0 for merge.
   */
  static int insert_delayed_ref(struct btrfs_trans_handle *trans,
  			      struct btrfs_delayed_ref_root *root,
  			      struct btrfs_delayed_ref_head *href,
  			      struct btrfs_delayed_ref_node *ref)
  {
  	struct btrfs_delayed_ref_node *exist;
  	int mod;
  	int ret = 0;
  
  	spin_lock(&href->lock);
  	exist = tree_insert(&href->ref_tree, ref);
  	if (!exist)
  		goto inserted;
  
  	/* Now we are sure we can merge */
  	ret = 1;
  	if (exist->action == ref->action) {
  		mod = ref->ref_mod;
  	} else {
  		/* Need to change action */
  		if (exist->ref_mod < ref->ref_mod) {
  			exist->action = ref->action;
  			mod = -exist->ref_mod;
  			exist->ref_mod = ref->ref_mod;
  			if (ref->action == BTRFS_ADD_DELAYED_REF)
  				list_add_tail(&exist->add_list,
  					      &href->ref_add_list);
  			else if (ref->action == BTRFS_DROP_DELAYED_REF) {
  				ASSERT(!list_empty(&exist->add_list));
  				list_del(&exist->add_list);
  			} else {
  				ASSERT(0);
  			}
  		} else
  			mod = -ref->ref_mod;
  	}
  	exist->ref_mod += mod;
  
  	/* remove existing tail if its ref_mod is zero */
  	if (exist->ref_mod == 0)
  		drop_delayed_ref(trans, root, href, exist);
  	spin_unlock(&href->lock);
  	return ret;
  inserted:
  	if (ref->action == BTRFS_ADD_DELAYED_REF)
  		list_add_tail(&ref->add_list, &href->ref_add_list);
  	atomic_inc(&root->num_entries);
  	spin_unlock(&href->lock);
  	return ret;
  }
  
  /*
   * helper function to update the accounting in the head ref
   * existing and update must have the same bytenr
   */
  static noinline void update_existing_head_ref(struct btrfs_trans_handle *trans,
  			 struct btrfs_delayed_ref_head *existing,
  			 struct btrfs_delayed_ref_head *update)
  {
  	struct btrfs_delayed_ref_root *delayed_refs =
  		&trans->transaction->delayed_refs;
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	u64 flags = btrfs_ref_head_to_space_flags(existing);
  	int old_ref_mod;
  
  	BUG_ON(existing->is_data != update->is_data);
  
  	spin_lock(&existing->lock);
  	if (update->must_insert_reserved) {
  		/* if the extent was freed and then
  		 * reallocated before the delayed ref
  		 * entries were processed, we can end up
  		 * with an existing head ref without
  		 * the must_insert_reserved flag set.
  		 * Set it again here
  		 */
  		existing->must_insert_reserved = update->must_insert_reserved;
  
  		/*
  		 * update the num_bytes so we make sure the accounting
  		 * is done correctly
  		 */
  		existing->num_bytes = update->num_bytes;
  
  	}
  
  	if (update->extent_op) {
  		if (!existing->extent_op) {
  			existing->extent_op = update->extent_op;
  		} else {
  			if (update->extent_op->update_key) {
  				memcpy(&existing->extent_op->key,
  				       &update->extent_op->key,
  				       sizeof(update->extent_op->key));
  				existing->extent_op->update_key = true;
  			}
  			if (update->extent_op->update_flags) {
  				existing->extent_op->flags_to_set |=
  					update->extent_op->flags_to_set;
  				existing->extent_op->update_flags = true;
  			}
  			btrfs_free_delayed_extent_op(update->extent_op);
  		}
  	}
  	/*
  	 * update the reference mod on the head to reflect this new operation,
  	 * only need the lock for this case cause we could be processing it
  	 * currently, for refs we just added we know we're a-ok.
  	 */
  	old_ref_mod = existing->total_ref_mod;
  	existing->ref_mod += update->ref_mod;
  	existing->total_ref_mod += update->ref_mod;
  
  	/*
  	 * If we are going to from a positive ref mod to a negative or vice
  	 * versa we need to make sure to adjust pending_csums accordingly.
  	 */
  	if (existing->is_data) {
  		u64 csum_leaves =
  			btrfs_csum_bytes_to_leaves(fs_info,
  						   existing->num_bytes);
  
  		if (existing->total_ref_mod >= 0 && old_ref_mod < 0) {
  			delayed_refs->pending_csums -= existing->num_bytes;
  			btrfs_delayed_refs_rsv_release(fs_info, csum_leaves);
  		}
  		if (existing->total_ref_mod < 0 && old_ref_mod >= 0) {
  			delayed_refs->pending_csums += existing->num_bytes;
  			trans->delayed_ref_updates += csum_leaves;
  		}
  	}
  
  	/*
  	 * This handles the following conditions:
  	 *
  	 * 1. We had a ref mod of 0 or more and went negative, indicating that
  	 *    we may be freeing space, so add our space to the
  	 *    total_bytes_pinned counter.
  	 * 2. We were negative and went to 0 or positive, so no longer can say
  	 *    that the space would be pinned, decrement our counter from the
  	 *    total_bytes_pinned counter.
  	 * 3. We are now at 0 and have ->must_insert_reserved set, which means
  	 *    this was a new allocation and then we dropped it, and thus must
  	 *    add our space to the total_bytes_pinned counter.
  	 */
  	if (existing->total_ref_mod < 0 && old_ref_mod >= 0)
  		btrfs_mod_total_bytes_pinned(fs_info, flags, existing->num_bytes);
  	else if (existing->total_ref_mod >= 0 && old_ref_mod < 0)
  		btrfs_mod_total_bytes_pinned(fs_info, flags, -existing->num_bytes);
  	else if (existing->total_ref_mod == 0 && existing->must_insert_reserved)
  		btrfs_mod_total_bytes_pinned(fs_info, flags, existing->num_bytes);
  
  	spin_unlock(&existing->lock);
  }
  
  static void init_delayed_ref_head(struct btrfs_delayed_ref_head *head_ref,
  				  struct btrfs_qgroup_extent_record *qrecord,
  				  u64 bytenr, u64 num_bytes, u64 ref_root,
  				  u64 reserved, int action, bool is_data,
  				  bool is_system)
  {
  	int count_mod = 1;
  	int must_insert_reserved = 0;
  
  	/* If reserved is provided, it must be a data extent. */
  	BUG_ON(!is_data && reserved);
  
  	/*
  	 * The head node stores the sum of all the mods, so dropping a ref
  	 * should drop the sum in the head node by one.
  	 */
  	if (action == BTRFS_UPDATE_DELAYED_HEAD)
  		count_mod = 0;
  	else if (action == BTRFS_DROP_DELAYED_REF)
  		count_mod = -1;
  
  	/*
  	 * BTRFS_ADD_DELAYED_EXTENT means that we need to update the reserved
  	 * accounting when the extent is finally added, or if a later
  	 * modification deletes the delayed ref without ever inserting the
  	 * extent into the extent allocation tree.  ref->must_insert_reserved
  	 * is the flag used to record that accounting mods are required.
  	 *
  	 * Once we record must_insert_reserved, switch the action to
  	 * BTRFS_ADD_DELAYED_REF because other special casing is not required.
  	 */
  	if (action == BTRFS_ADD_DELAYED_EXTENT)
  		must_insert_reserved = 1;
  	else
  		must_insert_reserved = 0;
  
  	refcount_set(&head_ref->refs, 1);
  	head_ref->bytenr = bytenr;
  	head_ref->num_bytes = num_bytes;
  	head_ref->ref_mod = count_mod;
  	head_ref->must_insert_reserved = must_insert_reserved;
  	head_ref->is_data = is_data;
  	head_ref->is_system = is_system;
  	head_ref->ref_tree = RB_ROOT_CACHED;
  	INIT_LIST_HEAD(&head_ref->ref_add_list);
  	RB_CLEAR_NODE(&head_ref->href_node);
  	head_ref->processing = 0;
  	head_ref->total_ref_mod = count_mod;
  	spin_lock_init(&head_ref->lock);
  	mutex_init(&head_ref->mutex);
  
  	if (qrecord) {
  		if (ref_root && reserved) {
  			qrecord->data_rsv = reserved;
  			qrecord->data_rsv_refroot = ref_root;
  		}
  		qrecord->bytenr = bytenr;
  		qrecord->num_bytes = num_bytes;
  		qrecord->old_roots = NULL;
  	}
  }
  
  /*
   * helper function to actually insert a head node into the rbtree.
   * this does all the dirty work in terms of maintaining the correct
   * overall modification count.
   */
  static noinline struct btrfs_delayed_ref_head *
  add_delayed_ref_head(struct btrfs_trans_handle *trans,
  		     struct btrfs_delayed_ref_head *head_ref,
  		     struct btrfs_qgroup_extent_record *qrecord,
  		     int action, int *qrecord_inserted_ret)
  {
  	struct btrfs_delayed_ref_head *existing;
  	struct btrfs_delayed_ref_root *delayed_refs;
  	int qrecord_inserted = 0;
  
  	delayed_refs = &trans->transaction->delayed_refs;
  
  	/* Record qgroup extent info if provided */
  	if (qrecord) {
  		if (btrfs_qgroup_trace_extent_nolock(trans->fs_info,
  					delayed_refs, qrecord))
  			kfree(qrecord);
  		else
  			qrecord_inserted = 1;
  	}
  
  	trace_add_delayed_ref_head(trans->fs_info, head_ref, action);
  
  	existing = htree_insert(&delayed_refs->href_root,
  				&head_ref->href_node);
  	if (existing) {
  		update_existing_head_ref(trans, existing, head_ref);
  		/*
  		 * we've updated the existing ref, free the newly
  		 * allocated ref
  		 */
  		kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
  		head_ref = existing;
  	} else {
  		u64 flags = btrfs_ref_head_to_space_flags(head_ref);
  
  		if (head_ref->is_data && head_ref->ref_mod < 0) {
  			delayed_refs->pending_csums += head_ref->num_bytes;
  			trans->delayed_ref_updates +=
  				btrfs_csum_bytes_to_leaves(trans->fs_info,
  							   head_ref->num_bytes);
  		}
  		if (head_ref->ref_mod < 0)
  			btrfs_mod_total_bytes_pinned(trans->fs_info, flags,
  						     head_ref->num_bytes);
  		delayed_refs->num_heads++;
  		delayed_refs->num_heads_ready++;
  		atomic_inc(&delayed_refs->num_entries);
  		trans->delayed_ref_updates++;
  	}
  	if (qrecord_inserted_ret)
  		*qrecord_inserted_ret = qrecord_inserted;
  
  	return head_ref;
  }
  
  /*
   * init_delayed_ref_common - Initialize the structure which represents a
   *			     modification to a an extent.
   *
   * @fs_info:    Internal to the mounted filesystem mount structure.
   *
   * @ref:	The structure which is going to be initialized.
   *
   * @bytenr:	The logical address of the extent for which a modification is
   *		going to be recorded.
   *
   * @num_bytes:  Size of the extent whose modification is being recorded.
   *
   * @ref_root:	The id of the root where this modification has originated, this
   *		can be either one of the well-known metadata trees or the
   *		subvolume id which references this extent.
   *
   * @action:	Can be one of BTRFS_ADD_DELAYED_REF/BTRFS_DROP_DELAYED_REF or
   *		BTRFS_ADD_DELAYED_EXTENT
   *
   * @ref_type:	Holds the type of the extent which is being recorded, can be
   *		one of BTRFS_SHARED_BLOCK_REF_KEY/BTRFS_TREE_BLOCK_REF_KEY
   *		when recording a metadata extent or BTRFS_SHARED_DATA_REF_KEY/
   *		BTRFS_EXTENT_DATA_REF_KEY when recording data extent
   */
  static void init_delayed_ref_common(struct btrfs_fs_info *fs_info,
  				    struct btrfs_delayed_ref_node *ref,
  				    u64 bytenr, u64 num_bytes, u64 ref_root,
  				    int action, u8 ref_type)
  {
  	u64 seq = 0;
  
  	if (action == BTRFS_ADD_DELAYED_EXTENT)
  		action = BTRFS_ADD_DELAYED_REF;
  
  	if (is_fstree(ref_root))
  		seq = atomic64_read(&fs_info->tree_mod_seq);
  
  	refcount_set(&ref->refs, 1);
  	ref->bytenr = bytenr;
  	ref->num_bytes = num_bytes;
  	ref->ref_mod = 1;
  	ref->action = action;
  	ref->is_head = 0;
  	ref->in_tree = 1;
  	ref->seq = seq;
  	ref->type = ref_type;
  	RB_CLEAR_NODE(&ref->ref_node);
  	INIT_LIST_HEAD(&ref->add_list);
  }
  
  /*
   * add a delayed tree ref.  This does all of the accounting required
   * to make sure the delayed ref is eventually processed before this
   * transaction commits.
   */
  int btrfs_add_delayed_tree_ref(struct btrfs_trans_handle *trans,
  			       struct btrfs_ref *generic_ref,
  			       struct btrfs_delayed_extent_op *extent_op)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_delayed_tree_ref *ref;
  	struct btrfs_delayed_ref_head *head_ref;
  	struct btrfs_delayed_ref_root *delayed_refs;
  	struct btrfs_qgroup_extent_record *record = NULL;
  	int qrecord_inserted;
  	bool is_system;
  	int action = generic_ref->action;
  	int level = generic_ref->tree_ref.level;
  	int ret;
  	u64 bytenr = generic_ref->bytenr;
  	u64 num_bytes = generic_ref->len;
  	u64 parent = generic_ref->parent;
  	u8 ref_type;
  
  	is_system = (generic_ref->real_root == BTRFS_CHUNK_TREE_OBJECTID);
  
  	ASSERT(generic_ref->type == BTRFS_REF_METADATA && generic_ref->action);
  	BUG_ON(extent_op && extent_op->is_data);
  	ref = kmem_cache_alloc(btrfs_delayed_tree_ref_cachep, GFP_NOFS);
  	if (!ref)
  		return -ENOMEM;
  
  	head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep, GFP_NOFS);
  	if (!head_ref) {
  		kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
  		return -ENOMEM;
  	}
  
  	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags) &&
  	    is_fstree(generic_ref->real_root) &&
  	    is_fstree(generic_ref->tree_ref.root) &&
  	    !generic_ref->skip_qgroup) {
  		record = kzalloc(sizeof(*record), GFP_NOFS);
  		if (!record) {
  			kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
  			kmem_cache_free(btrfs_delayed_ref_head_cachep, head_ref);
  			return -ENOMEM;
  		}
  	}
  
  	if (parent)
  		ref_type = BTRFS_SHARED_BLOCK_REF_KEY;
  	else
  		ref_type = BTRFS_TREE_BLOCK_REF_KEY;
  
  	init_delayed_ref_common(fs_info, &ref->node, bytenr, num_bytes,
  				generic_ref->tree_ref.root, action, ref_type);
  	ref->root = generic_ref->tree_ref.root;
  	ref->parent = parent;
  	ref->level = level;
  
  	init_delayed_ref_head(head_ref, record, bytenr, num_bytes,
  			      generic_ref->tree_ref.root, 0, action, false,
  			      is_system);
  	head_ref->extent_op = extent_op;
  
  	delayed_refs = &trans->transaction->delayed_refs;
  	spin_lock(&delayed_refs->lock);
  
  	/*
  	 * insert both the head node and the new ref without dropping
  	 * the spin lock
  	 */
  	head_ref = add_delayed_ref_head(trans, head_ref, record,
  					action, &qrecord_inserted);
  
  	ret = insert_delayed_ref(trans, delayed_refs, head_ref, &ref->node);
  	spin_unlock(&delayed_refs->lock);
  
  	/*
  	 * Need to update the delayed_refs_rsv with any changes we may have
  	 * made.
  	 */
  	btrfs_update_delayed_refs_rsv(trans);
  
  	trace_add_delayed_tree_ref(fs_info, &ref->node, ref,
  				   action == BTRFS_ADD_DELAYED_EXTENT ?
  				   BTRFS_ADD_DELAYED_REF : action);
  	if (ret > 0)
  		kmem_cache_free(btrfs_delayed_tree_ref_cachep, ref);
  
  	if (qrecord_inserted)
  		btrfs_qgroup_trace_extent_post(trans, record);
  
  	return 0;
  }
  
  /*
   * add a delayed data ref. it's similar to btrfs_add_delayed_tree_ref.
   */
  int btrfs_add_delayed_data_ref(struct btrfs_trans_handle *trans,
  			       struct btrfs_ref *generic_ref,
  			       u64 reserved)
  {
  	struct btrfs_fs_info *fs_info = trans->fs_info;
  	struct btrfs_delayed_data_ref *ref;
  	struct btrfs_delayed_ref_head *head_ref;
  	struct btrfs_delayed_ref_root *delayed_refs;
  	struct btrfs_qgroup_extent_record *record = NULL;
  	int qrecord_inserted;
  	int action = generic_ref->action;
  	int ret;
  	u64 bytenr = generic_ref->bytenr;
  	u64 num_bytes = generic_ref->len;
  	u64 parent = generic_ref->parent;
  	u64 ref_root = generic_ref->data_ref.ref_root;
  	u64 owner = generic_ref->data_ref.ino;
  	u64 offset = generic_ref->data_ref.offset;
  	u8 ref_type;
  
  	ASSERT(generic_ref->type == BTRFS_REF_DATA && action);
  	ref = kmem_cache_alloc(btrfs_delayed_data_ref_cachep, GFP_NOFS);
  	if (!ref)
  		return -ENOMEM;
  
  	if (parent)
  	        ref_type = BTRFS_SHARED_DATA_REF_KEY;
  	else
  	        ref_type = BTRFS_EXTENT_DATA_REF_KEY;
  	init_delayed_ref_common(fs_info, &ref->node, bytenr, num_bytes,
  				ref_root, action, ref_type);
  	ref->root = ref_root;
  	ref->parent = parent;
  	ref->objectid = owner;
  	ref->offset = offset;
  
  
  	head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep, GFP_NOFS);
  	if (!head_ref) {
  		kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
  		return -ENOMEM;
  	}
  
  	if (test_bit(BTRFS_FS_QUOTA_ENABLED, &fs_info->flags) &&
  	    is_fstree(ref_root) &&
  	    is_fstree(generic_ref->real_root) &&
  	    !generic_ref->skip_qgroup) {
  		record = kzalloc(sizeof(*record), GFP_NOFS);
  		if (!record) {
  			kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
  			kmem_cache_free(btrfs_delayed_ref_head_cachep,
  					head_ref);
  			return -ENOMEM;
  		}
  	}
  
  	init_delayed_ref_head(head_ref, record, bytenr, num_bytes, ref_root,
  			      reserved, action, true, false);
  	head_ref->extent_op = NULL;
  
  	delayed_refs = &trans->transaction->delayed_refs;
  	spin_lock(&delayed_refs->lock);
  
  	/*
  	 * insert both the head node and the new ref without dropping
  	 * the spin lock
  	 */
  	head_ref = add_delayed_ref_head(trans, head_ref, record,
  					action, &qrecord_inserted);
  
  	ret = insert_delayed_ref(trans, delayed_refs, head_ref, &ref->node);
  	spin_unlock(&delayed_refs->lock);
  
  	/*
  	 * Need to update the delayed_refs_rsv with any changes we may have
  	 * made.
  	 */
  	btrfs_update_delayed_refs_rsv(trans);
  
  	trace_add_delayed_data_ref(trans->fs_info, &ref->node, ref,
  				   action == BTRFS_ADD_DELAYED_EXTENT ?
  				   BTRFS_ADD_DELAYED_REF : action);
  	if (ret > 0)
  		kmem_cache_free(btrfs_delayed_data_ref_cachep, ref);
  
  
  	if (qrecord_inserted)
  		return btrfs_qgroup_trace_extent_post(trans, record);
  	return 0;
  }
  
  int btrfs_add_delayed_extent_op(struct btrfs_trans_handle *trans,
  				u64 bytenr, u64 num_bytes,
  				struct btrfs_delayed_extent_op *extent_op)
  {
  	struct btrfs_delayed_ref_head *head_ref;
  	struct btrfs_delayed_ref_root *delayed_refs;
  
  	head_ref = kmem_cache_alloc(btrfs_delayed_ref_head_cachep, GFP_NOFS);
  	if (!head_ref)
  		return -ENOMEM;
  
  	init_delayed_ref_head(head_ref, NULL, bytenr, num_bytes, 0, 0,
  			      BTRFS_UPDATE_DELAYED_HEAD, extent_op->is_data,
  			      false);
  	head_ref->extent_op = extent_op;
  
  	delayed_refs = &trans->transaction->delayed_refs;
  	spin_lock(&delayed_refs->lock);
  
  	add_delayed_ref_head(trans, head_ref, NULL, BTRFS_UPDATE_DELAYED_HEAD,
  			     NULL);
  
  	spin_unlock(&delayed_refs->lock);
  
  	/*
  	 * Need to update the delayed_refs_rsv with any changes we may have
  	 * made.
  	 */
  	btrfs_update_delayed_refs_rsv(trans);
  	return 0;
  }
  
  /*
   * This does a simple search for the head node for a given extent.  Returns the
   * head node if found, or NULL if not.
   */
  struct btrfs_delayed_ref_head *
  btrfs_find_delayed_ref_head(struct btrfs_delayed_ref_root *delayed_refs, u64 bytenr)
  {
  	lockdep_assert_held(&delayed_refs->lock);
  
  	return find_ref_head(delayed_refs, bytenr, false);
  }
  
  void __cold btrfs_delayed_ref_exit(void)
  {
  	kmem_cache_destroy(btrfs_delayed_ref_head_cachep);
  	kmem_cache_destroy(btrfs_delayed_tree_ref_cachep);
  	kmem_cache_destroy(btrfs_delayed_data_ref_cachep);
  	kmem_cache_destroy(btrfs_delayed_extent_op_cachep);
  }
  
  int __init btrfs_delayed_ref_init(void)
  {
  	btrfs_delayed_ref_head_cachep = kmem_cache_create(
  				"btrfs_delayed_ref_head",
  				sizeof(struct btrfs_delayed_ref_head), 0,
  				SLAB_MEM_SPREAD, NULL);
  	if (!btrfs_delayed_ref_head_cachep)
  		goto fail;
  
  	btrfs_delayed_tree_ref_cachep = kmem_cache_create(
  				"btrfs_delayed_tree_ref",
  				sizeof(struct btrfs_delayed_tree_ref), 0,
  				SLAB_MEM_SPREAD, NULL);
  	if (!btrfs_delayed_tree_ref_cachep)
  		goto fail;
  
  	btrfs_delayed_data_ref_cachep = kmem_cache_create(
  				"btrfs_delayed_data_ref",
  				sizeof(struct btrfs_delayed_data_ref), 0,
  				SLAB_MEM_SPREAD, NULL);
  	if (!btrfs_delayed_data_ref_cachep)
  		goto fail;
  
  	btrfs_delayed_extent_op_cachep = kmem_cache_create(
  				"btrfs_delayed_extent_op",
  				sizeof(struct btrfs_delayed_extent_op), 0,
  				SLAB_MEM_SPREAD, NULL);
  	if (!btrfs_delayed_extent_op_cachep)
  		goto fail;
  
  	return 0;
  fail:
  	btrfs_delayed_ref_exit();
  	return -ENOMEM;
  }
  