jbd2: fast commit recovery path

[mirror_ubuntu-jammy-kernel.git] / fs / btrfs / delayed-ref.c

// 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"

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);
}

/**
 * btrfs_delayed_refs_rsv_release - release a ref head's reservation.
 * @fs_info - the fs_info for our fs.
 * @nr - the 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;
}

/**
 * btrfs_migrate_to_delayed_refs_rsv - transfer bytes to our delayed refs rsv.
 * @fs_info - the fs info for our fs.
 * @src - the source block rsv to transfer from.
 * @num_bytes - the 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);
}

/**
 * btrfs_delayed_refs_rsv_refill - refill based on our delayed refs usage.
 * @fs_info - the fs_info for our fs.
 * @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;

        read_lock(&fs_info->tree_mod_log_lock);
        if (!list_empty(&fs_info->tree_mod_seq_list)) {
                struct seq_list *elem;

                elem = list_first_entry(&fs_info->tree_mod_seq_list,
                                        struct seq_list, list);
                seq = elem->seq;
        }
        read_unlock(&fs_info->tree_mod_log_lock);

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)
{
        struct seq_list *elem;
        int ret = 0;

        read_lock(&fs_info->tree_mod_log_lock);
        if (!list_empty(&fs_info->tree_mod_seq_list)) {
                elem = list_first_entry(&fs_info->tree_mod_seq_list,
                                        struct seq_list, list);
                if (seq >= elem->seq) {
                        btrfs_debug(fs_info,
                                "holding back delayed_ref %#x.%x, lowest is %#x.%x",
                                (u32)(seq >> 32), (u32)seq,
                                (u32)(elem->seq >> 32), (u32)elem->seq);
                        ret = 1;
                }
        }

        read_unlock(&fs_info->tree_mod_log_lock);
        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,
                         int *old_ref_mod_ret)
{
        struct btrfs_delayed_ref_root *delayed_refs =
                &trans->transaction->delayed_refs;
        struct btrfs_fs_info *fs_info = trans->fs_info;
        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;
        if (old_ref_mod_ret)
                *old_ref_mod_ret = old_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;
                }
        }
        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,
                     int *old_ref_mod, int *new_ref_mod)
{
        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,
                                         old_ref_mod);
                /*
                 * 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 {
                if (old_ref_mod)
                        *old_ref_mod = 0;
                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);
                }
                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;
        if (new_ref_mod)
                *new_ref_mod = head_ref->total_ref_mod;

        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,
                               int *old_ref_mod, int *new_ref_mod)
{
        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,
                                        old_ref_mod, new_ref_mod);

        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(fs_info, 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, int *old_ref_mod,
                               int *new_ref_mod)
{
        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,
                                        old_ref_mod, new_ref_mod);

        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(fs_info, 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, NULL, 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;
}