[bcachefs-tools-debian] / libbcachefs / btree_update_interior.c

// SPDX-License-Identifier: GPL-2.0

#include "bcachefs.h"
#include "alloc_foreground.h"
#include "bkey_methods.h"
#include "btree_cache.h"
#include "btree_gc.h"
#include "btree_update.h"
#include "btree_update_interior.h"
#include "btree_io.h"
#include "btree_iter.h"
#include "btree_locking.h"
#include "buckets.h"
#include "extents.h"
#include "journal.h"
#include "journal_reclaim.h"
#include "keylist.h"
#include "replicas.h"
#include "super-io.h"

#include <linux/random.h>
#include <trace/events/bcachefs.h>

/* Debug code: */

/*
 * Verify that child nodes correctly span parent node's range:
 */
static void btree_node_interior_verify(struct bch_fs *c, struct btree *b)
{
#ifdef CONFIG_BCACHEFS_DEBUG
        struct bpos next_node = b->data->min_key;
        struct btree_node_iter iter;
        struct bkey_s_c k;
        struct bkey_s_c_btree_ptr_v2 bp;
        struct bkey unpacked;

        BUG_ON(!b->c.level);

        if (!test_bit(BCH_FS_BTREE_INTERIOR_REPLAY_DONE, &c->flags))
                return;

        bch2_btree_node_iter_init_from_start(&iter, b);

        while (1) {
                k = bch2_btree_node_iter_peek_unpack(&iter, b, &unpacked);
                if (k.k->type != KEY_TYPE_btree_ptr_v2)
                        break;
                bp = bkey_s_c_to_btree_ptr_v2(k);

                BUG_ON(bkey_cmp(next_node, bp.v->min_key));

                bch2_btree_node_iter_advance(&iter, b);

                if (bch2_btree_node_iter_end(&iter)) {
                        BUG_ON(bkey_cmp(k.k->p, b->key.k.p));
                        break;
                }

                next_node = bkey_successor(k.k->p);
        }
#endif
}

/* Calculate ideal packed bkey format for new btree nodes: */

void __bch2_btree_calc_format(struct bkey_format_state *s, struct btree *b)
{
        struct bkey_packed *k;
        struct bset_tree *t;
        struct bkey uk;

        bch2_bkey_format_add_pos(s, b->data->min_key);

        for_each_bset(b, t)
                bset_tree_for_each_key(b, t, k)
                        if (!bkey_whiteout(k)) {
                                uk = bkey_unpack_key(b, k);
                                bch2_bkey_format_add_key(s, &uk);
                        }
}

static struct bkey_format bch2_btree_calc_format(struct btree *b)
{
        struct bkey_format_state s;

        bch2_bkey_format_init(&s);
        __bch2_btree_calc_format(&s, b);

        return bch2_bkey_format_done(&s);
}

static size_t btree_node_u64s_with_format(struct btree *b,
                                          struct bkey_format *new_f)
{
        struct bkey_format *old_f = &b->format;

        /* stupid integer promotion rules */
        ssize_t delta =
            (((int) new_f->key_u64s - old_f->key_u64s) *
             (int) b->nr.packed_keys) +
            (((int) new_f->key_u64s - BKEY_U64s) *
             (int) b->nr.unpacked_keys);

        BUG_ON(delta + b->nr.live_u64s < 0);

        return b->nr.live_u64s + delta;
}

/**
 * btree_node_format_fits - check if we could rewrite node with a new format
 *
 * This assumes all keys can pack with the new format -- it just checks if
 * the re-packed keys would fit inside the node itself.
 */
bool bch2_btree_node_format_fits(struct bch_fs *c, struct btree *b,
                                 struct bkey_format *new_f)
{
        size_t u64s = btree_node_u64s_with_format(b, new_f);

        return __vstruct_bytes(struct btree_node, u64s) < btree_bytes(c);
}

/* Btree node freeing/allocation: */

static void __btree_node_free(struct bch_fs *c, struct btree *b)
{
        trace_btree_node_free(c, b);

        BUG_ON(btree_node_dirty(b));
        BUG_ON(btree_node_need_write(b));
        BUG_ON(b == btree_node_root(c, b));
        BUG_ON(b->ob.nr);
        BUG_ON(!list_empty(&b->write_blocked));
        BUG_ON(b->will_make_reachable);

        clear_btree_node_noevict(b);

        bch2_btree_node_hash_remove(&c->btree_cache, b);

        mutex_lock(&c->btree_cache.lock);
        list_move(&b->list, &c->btree_cache.freeable);
        mutex_unlock(&c->btree_cache.lock);
}

void bch2_btree_node_free_never_inserted(struct bch_fs *c, struct btree *b)
{
        struct open_buckets ob = b->ob;

        b->ob.nr = 0;

        clear_btree_node_dirty(b);

        btree_node_lock_type(c, b, SIX_LOCK_write);
        __btree_node_free(c, b);
        six_unlock_write(&b->c.lock);

        bch2_open_buckets_put(c, &ob);
}

void bch2_btree_node_free_inmem(struct bch_fs *c, struct btree *b,
                                struct btree_iter *iter)
{
        struct btree_iter *linked;

        trans_for_each_iter(iter->trans, linked)
                BUG_ON(linked->l[b->c.level].b == b);

        six_lock_write(&b->c.lock, NULL, NULL);
        __btree_node_free(c, b);
        six_unlock_write(&b->c.lock);
        six_unlock_intent(&b->c.lock);
}

static struct btree *__bch2_btree_node_alloc(struct bch_fs *c,
                                             struct disk_reservation *res,
                                             struct closure *cl,
                                             unsigned flags)
{
        struct write_point *wp;
        struct btree *b;
        BKEY_PADDED(k) tmp;
        struct open_buckets ob = { .nr = 0 };
        struct bch_devs_list devs_have = (struct bch_devs_list) { 0 };
        unsigned nr_reserve;
        enum alloc_reserve alloc_reserve;

        if (flags & BTREE_INSERT_USE_ALLOC_RESERVE) {
                nr_reserve      = 0;
                alloc_reserve   = RESERVE_ALLOC;
        } else if (flags & BTREE_INSERT_USE_RESERVE) {
                nr_reserve      = BTREE_NODE_RESERVE / 2;
                alloc_reserve   = RESERVE_BTREE;
        } else {
                nr_reserve      = BTREE_NODE_RESERVE;
                alloc_reserve   = RESERVE_NONE;
        }

        mutex_lock(&c->btree_reserve_cache_lock);
        if (c->btree_reserve_cache_nr > nr_reserve) {
                struct btree_alloc *a =
                        &c->btree_reserve_cache[--c->btree_reserve_cache_nr];

                ob = a->ob;
                bkey_copy(&tmp.k, &a->k);
                mutex_unlock(&c->btree_reserve_cache_lock);
                goto mem_alloc;
        }
        mutex_unlock(&c->btree_reserve_cache_lock);

retry:
        wp = bch2_alloc_sectors_start(c, c->opts.foreground_target, 0,
                                      writepoint_ptr(&c->btree_write_point),
                                      &devs_have,
                                      res->nr_replicas,
                                      c->opts.metadata_replicas_required,
                                      alloc_reserve, 0, cl);
        if (IS_ERR(wp))
                return ERR_CAST(wp);

        if (wp->sectors_free < c->opts.btree_node_size) {
                struct open_bucket *ob;
                unsigned i;

                open_bucket_for_each(c, &wp->ptrs, ob, i)
                        if (ob->sectors_free < c->opts.btree_node_size)
                                ob->sectors_free = 0;

                bch2_alloc_sectors_done(c, wp);
                goto retry;
        }

        if (c->sb.features & (1ULL << BCH_FEATURE_btree_ptr_v2))
                bkey_btree_ptr_v2_init(&tmp.k);
        else
                bkey_btree_ptr_init(&tmp.k);

        bch2_alloc_sectors_append_ptrs(c, wp, &tmp.k, c->opts.btree_node_size);

        bch2_open_bucket_get(c, wp, &ob);
        bch2_alloc_sectors_done(c, wp);
mem_alloc:
        b = bch2_btree_node_mem_alloc(c);

        /* we hold cannibalize_lock: */
        BUG_ON(IS_ERR(b));
        BUG_ON(b->ob.nr);

        bkey_copy(&b->key, &tmp.k);
        b->ob = ob;

        return b;
}

static struct btree *bch2_btree_node_alloc(struct btree_update *as, unsigned level)
{
        struct bch_fs *c = as->c;
        struct btree *b;
        int ret;

        BUG_ON(level >= BTREE_MAX_DEPTH);
        BUG_ON(!as->nr_prealloc_nodes);

        b = as->prealloc_nodes[--as->nr_prealloc_nodes];

        set_btree_node_accessed(b);
        set_btree_node_dirty(b);
        set_btree_node_need_write(b);

        bch2_bset_init_first(b, &b->data->keys);
        b->c.level      = level;
        b->c.btree_id   = as->btree_id;

        memset(&b->nr, 0, sizeof(b->nr));
        b->data->magic = cpu_to_le64(bset_magic(c));
        b->data->flags = 0;
        SET_BTREE_NODE_ID(b->data, as->btree_id);
        SET_BTREE_NODE_LEVEL(b->data, level);
        b->data->ptr = bch2_bkey_ptrs_c(bkey_i_to_s_c(&b->key)).start->ptr;

        if (b->key.k.type == KEY_TYPE_btree_ptr_v2) {
                struct bkey_i_btree_ptr_v2 *bp = bkey_i_to_btree_ptr_v2(&b->key);

                bp->v.mem_ptr           = 0;
                bp->v.seq               = b->data->keys.seq;
                bp->v.sectors_written   = 0;
                bp->v.sectors           = cpu_to_le16(c->opts.btree_node_size);
        }

        if (c->sb.features & (1ULL << BCH_FEATURE_new_extent_overwrite))
                SET_BTREE_NODE_NEW_EXTENT_OVERWRITE(b->data, true);

        if (btree_node_is_extents(b) &&
            !BTREE_NODE_NEW_EXTENT_OVERWRITE(b->data)) {
                set_btree_node_old_extent_overwrite(b);
                set_btree_node_need_rewrite(b);
        }

        bch2_btree_build_aux_trees(b);

        ret = bch2_btree_node_hash_insert(&c->btree_cache, b, level, as->btree_id);
        BUG_ON(ret);

        trace_btree_node_alloc(c, b);
        return b;
}

static void btree_set_min(struct btree *b, struct bpos pos)
{
        if (b->key.k.type == KEY_TYPE_btree_ptr_v2)
                bkey_i_to_btree_ptr_v2(&b->key)->v.min_key = pos;
        b->data->min_key = pos;
}

static void btree_set_max(struct btree *b, struct bpos pos)
{
        b->key.k.p = pos;
        b->data->max_key = pos;
}

struct btree *__bch2_btree_node_alloc_replacement(struct btree_update *as,
                                                  struct btree *b,
                                                  struct bkey_format format)
{
        struct btree *n;

        n = bch2_btree_node_alloc(as, b->c.level);

        SET_BTREE_NODE_SEQ(n->data, BTREE_NODE_SEQ(b->data) + 1);

        btree_set_min(n, b->data->min_key);
        btree_set_max(n, b->data->max_key);

        n->data->format         = format;
        btree_node_set_format(n, format);

        bch2_btree_sort_into(as->c, n, b);

        btree_node_reset_sib_u64s(n);

        n->key.k.p = b->key.k.p;
        return n;
}

static struct btree *bch2_btree_node_alloc_replacement(struct btree_update *as,
                                                       struct btree *b)
{
        struct bkey_format new_f = bch2_btree_calc_format(b);

        /*
         * The keys might expand with the new format - if they wouldn't fit in
         * the btree node anymore, use the old format for now:
         */
        if (!bch2_btree_node_format_fits(as->c, b, &new_f))
                new_f = b->format;

        return __bch2_btree_node_alloc_replacement(as, b, new_f);
}

static struct btree *__btree_root_alloc(struct btree_update *as, unsigned level)
{
        struct btree *b = bch2_btree_node_alloc(as, level);

        btree_set_min(b, POS_MIN);
        btree_set_max(b, POS_MAX);
        b->data->format = bch2_btree_calc_format(b);

        btree_node_set_format(b, b->data->format);
        bch2_btree_build_aux_trees(b);

        bch2_btree_update_add_new_node(as, b);
        six_unlock_write(&b->c.lock);

        return b;
}

static void bch2_btree_reserve_put(struct btree_update *as)
{
        struct bch_fs *c = as->c;

        mutex_lock(&c->btree_reserve_cache_lock);

        while (as->nr_prealloc_nodes) {
                struct btree *b = as->prealloc_nodes[--as->nr_prealloc_nodes];

                six_unlock_write(&b->c.lock);

                if (c->btree_reserve_cache_nr <
                    ARRAY_SIZE(c->btree_reserve_cache)) {
                        struct btree_alloc *a =
                                &c->btree_reserve_cache[c->btree_reserve_cache_nr++];

                        a->ob = b->ob;
                        b->ob.nr = 0;
                        bkey_copy(&a->k, &b->key);
                } else {
                        bch2_open_buckets_put(c, &b->ob);
                }

                btree_node_lock_type(c, b, SIX_LOCK_write);
                __btree_node_free(c, b);
                six_unlock_write(&b->c.lock);

                six_unlock_intent(&b->c.lock);
        }

        mutex_unlock(&c->btree_reserve_cache_lock);
}

static int bch2_btree_reserve_get(struct btree_update *as, unsigned nr_nodes,
                                  unsigned flags, struct closure *cl)
{
        struct bch_fs *c = as->c;
        struct btree *b;
        int ret;

        BUG_ON(nr_nodes > BTREE_RESERVE_MAX);

        /*
         * Protects reaping from the btree node cache and using the btree node
         * open bucket reserve:
         */
        ret = bch2_btree_cache_cannibalize_lock(c, cl);
        if (ret)
                return ret;

        while (as->nr_prealloc_nodes < nr_nodes) {
                b = __bch2_btree_node_alloc(c, &as->disk_res,
                                            flags & BTREE_INSERT_NOWAIT
                                            ? NULL : cl, flags);
                if (IS_ERR(b)) {
                        ret = PTR_ERR(b);
                        goto err_free;
                }

                ret = bch2_mark_bkey_replicas(c, bkey_i_to_s_c(&b->key));
                if (ret)
                        goto err_free;

                as->prealloc_nodes[as->nr_prealloc_nodes++] = b;
        }

        bch2_btree_cache_cannibalize_unlock(c);
        return 0;
err_free:
        bch2_btree_cache_cannibalize_unlock(c);
        trace_btree_reserve_get_fail(c, nr_nodes, cl);
        return ret;
}

/* Asynchronous interior node update machinery */

static void bch2_btree_update_free(struct btree_update *as)
{
        struct bch_fs *c = as->c;

        bch2_journal_preres_put(&c->journal, &as->journal_preres);

        bch2_journal_pin_drop(&c->journal, &as->journal);
        bch2_journal_pin_flush(&c->journal, &as->journal);
        bch2_disk_reservation_put(c, &as->disk_res);
        bch2_btree_reserve_put(as);

        mutex_lock(&c->btree_interior_update_lock);
        list_del(&as->unwritten_list);
        list_del(&as->list);
        mutex_unlock(&c->btree_interior_update_lock);

        closure_debug_destroy(&as->cl);
        mempool_free(as, &c->btree_interior_update_pool);

        closure_wake_up(&c->btree_interior_update_wait);
}

static void btree_update_will_delete_key(struct btree_update *as,
                                         struct bkey_i *k)
{
        BUG_ON(bch2_keylist_u64s(&as->old_keys) + k->k.u64s >
               ARRAY_SIZE(as->_old_keys));
        bch2_keylist_add(&as->old_keys, k);
}

static void btree_update_will_add_key(struct btree_update *as,
                                      struct bkey_i *k)
{
        BUG_ON(bch2_keylist_u64s(&as->new_keys) + k->k.u64s >
               ARRAY_SIZE(as->_new_keys));
        bch2_keylist_add(&as->new_keys, k);
}

/*
 * The transactional part of an interior btree node update, where we journal the
 * update we did to the interior node and update alloc info:
 */
static int btree_update_nodes_written_trans(struct btree_trans *trans,
                                            struct btree_update *as)
{
        struct bkey_i *k;
        int ret;

        trans->extra_journal_entries = (void *) &as->journal_entries[0];
        trans->extra_journal_entry_u64s = as->journal_u64s;
        trans->journal_pin = &as->journal;

        for_each_keylist_key(&as->new_keys, k) {
                ret = bch2_trans_mark_key(trans, bkey_i_to_s_c(k),
                                          0, 0, BTREE_TRIGGER_INSERT);
                if (ret)
                        return ret;
        }

        for_each_keylist_key(&as->old_keys, k) {
                ret = bch2_trans_mark_key(trans, bkey_i_to_s_c(k),
                                          0, 0, BTREE_TRIGGER_OVERWRITE);
                if (ret)
                        return ret;
        }

        return 0;
}

static void btree_update_nodes_written(struct btree_update *as)
{
        struct bch_fs *c = as->c;
        struct btree *b = as->b;
        u64 journal_seq = 0;
        unsigned i;
        int ret;

        /*
         * We did an update to a parent node where the pointers we added pointed
         * to child nodes that weren't written yet: now, the child nodes have
         * been written so we can write out the update to the interior node.
         */

        /*
         * We can't call into journal reclaim here: we'd block on the journal
         * reclaim lock, but we may need to release the open buckets we have
         * pinned in order for other btree updates to make forward progress, and
         * journal reclaim does btree updates when flushing bkey_cached entries,
         * which may require allocations as well.
         */
        ret = bch2_trans_do(c, &as->disk_res, &journal_seq,
                            BTREE_INSERT_NOFAIL|
                            BTREE_INSERT_USE_RESERVE|
                            BTREE_INSERT_USE_ALLOC_RESERVE|
                            BTREE_INSERT_NOCHECK_RW|
                            BTREE_INSERT_JOURNAL_RECLAIM|
                            BTREE_INSERT_JOURNAL_RESERVED,
                            btree_update_nodes_written_trans(&trans, as));
        BUG_ON(ret && !bch2_journal_error(&c->journal));

        if (b) {
                /*
                 * @b is the node we did the final insert into:
                 *
                 * On failure to get a journal reservation, we still have to
                 * unblock the write and allow most of the write path to happen
                 * so that shutdown works, but the i->journal_seq mechanism
                 * won't work to prevent the btree write from being visible (we
                 * didn't get a journal sequence number) - instead
                 * __bch2_btree_node_write() doesn't do the actual write if
                 * we're in journal error state:
                 */

                btree_node_lock_type(c, b, SIX_LOCK_intent);
                btree_node_lock_type(c, b, SIX_LOCK_write);
                mutex_lock(&c->btree_interior_update_lock);

                list_del(&as->write_blocked_list);

                if (!ret && as->b == b) {
                        struct bset *i = btree_bset_last(b);

                        BUG_ON(!b->c.level);
                        BUG_ON(!btree_node_dirty(b));

                        i->journal_seq = cpu_to_le64(
                                max(journal_seq,
                                    le64_to_cpu(i->journal_seq)));

                        bch2_btree_add_journal_pin(c, b, journal_seq);
                }

                mutex_unlock(&c->btree_interior_update_lock);
                six_unlock_write(&b->c.lock);

                btree_node_write_if_need(c, b, SIX_LOCK_intent);
                six_unlock_intent(&b->c.lock);
        }

        bch2_journal_pin_drop(&c->journal, &as->journal);

        bch2_journal_preres_put(&c->journal, &as->journal_preres);

        mutex_lock(&c->btree_interior_update_lock);
        for (i = 0; i < as->nr_new_nodes; i++) {
                b = as->new_nodes[i];

                BUG_ON(b->will_make_reachable != (unsigned long) as);
                b->will_make_reachable = 0;
        }
        mutex_unlock(&c->btree_interior_update_lock);

        for (i = 0; i < as->nr_new_nodes; i++) {
                b = as->new_nodes[i];

                btree_node_lock_type(c, b, SIX_LOCK_read);
                btree_node_write_if_need(c, b, SIX_LOCK_read);
                six_unlock_read(&b->c.lock);
        }

        for (i = 0; i < as->nr_open_buckets; i++)
                bch2_open_bucket_put(c, c->open_buckets + as->open_buckets[i]);

        bch2_btree_update_free(as);
}

static void btree_interior_update_work(struct work_struct *work)
{
        struct bch_fs *c =
                container_of(work, struct bch_fs, btree_interior_update_work);
        struct btree_update *as;

        while (1) {
                mutex_lock(&c->btree_interior_update_lock);
                as = list_first_entry_or_null(&c->btree_interior_updates_unwritten,
                                              struct btree_update, unwritten_list);
                if (as && !as->nodes_written)
                        as = NULL;
                mutex_unlock(&c->btree_interior_update_lock);

                if (!as)
                        break;

                btree_update_nodes_written(as);
        }
}

static void btree_update_set_nodes_written(struct closure *cl)
{
        struct btree_update *as = container_of(cl, struct btree_update, cl);
        struct bch_fs *c = as->c;

        mutex_lock(&c->btree_interior_update_lock);
        as->nodes_written = true;
        mutex_unlock(&c->btree_interior_update_lock);

        queue_work(c->btree_interior_update_worker, &c->btree_interior_update_work);
}

/*
 * We're updating @b with pointers to nodes that haven't finished writing yet:
 * block @b from being written until @as completes
 */
static void btree_update_updated_node(struct btree_update *as, struct btree *b)
{
        struct bch_fs *c = as->c;

        mutex_lock(&c->btree_interior_update_lock);
        list_add_tail(&as->unwritten_list, &c->btree_interior_updates_unwritten);

        BUG_ON(as->mode != BTREE_INTERIOR_NO_UPDATE);
        BUG_ON(!btree_node_dirty(b));

        as->mode        = BTREE_INTERIOR_UPDATING_NODE;
        as->b           = b;
        list_add(&as->write_blocked_list, &b->write_blocked);

        mutex_unlock(&c->btree_interior_update_lock);
}

static void btree_update_reparent(struct btree_update *as,
                                  struct btree_update *child)
{
        struct bch_fs *c = as->c;

        lockdep_assert_held(&c->btree_interior_update_lock);

        child->b = NULL;
        child->mode = BTREE_INTERIOR_UPDATING_AS;

        /*
         * When we write a new btree root, we have to drop our journal pin
         * _before_ the new nodes are technically reachable; see
         * btree_update_nodes_written().
         *
         * This goes for journal pins that are recursively blocked on us - so,
         * just transfer the journal pin to the new interior update so
         * btree_update_nodes_written() can drop it.
         */
        bch2_journal_pin_copy(&c->journal, &as->journal, &child->journal, NULL);
        bch2_journal_pin_drop(&c->journal, &child->journal);
}

static void btree_update_updated_root(struct btree_update *as, struct btree *b)
{
        struct bkey_i *insert = &b->key;
        struct bch_fs *c = as->c;

        BUG_ON(as->mode != BTREE_INTERIOR_NO_UPDATE);

        BUG_ON(as->journal_u64s + jset_u64s(insert->k.u64s) >
               ARRAY_SIZE(as->journal_entries));

        as->journal_u64s +=
                journal_entry_set((void *) &as->journal_entries[as->journal_u64s],
                                  BCH_JSET_ENTRY_btree_root,
                                  b->c.btree_id, b->c.level,
                                  insert, insert->k.u64s);

        mutex_lock(&c->btree_interior_update_lock);
        list_add_tail(&as->unwritten_list, &c->btree_interior_updates_unwritten);

        as->mode        = BTREE_INTERIOR_UPDATING_ROOT;
        mutex_unlock(&c->btree_interior_update_lock);
}

/*
 * bch2_btree_update_add_new_node:
 *
 * This causes @as to wait on @b to be written, before it gets to
 * bch2_btree_update_nodes_written
 *
 * Additionally, it sets b->will_make_reachable to prevent any additional writes
 * to @b from happening besides the first until @b is reachable on disk
 *
 * And it adds @b to the list of @as's new nodes, so that we can update sector
 * counts in bch2_btree_update_nodes_written:
 */
void bch2_btree_update_add_new_node(struct btree_update *as, struct btree *b)
{
        struct bch_fs *c = as->c;

        closure_get(&as->cl);

        mutex_lock(&c->btree_interior_update_lock);
        BUG_ON(as->nr_new_nodes >= ARRAY_SIZE(as->new_nodes));
        BUG_ON(b->will_make_reachable);

        as->new_nodes[as->nr_new_nodes++] = b;
        b->will_make_reachable = 1UL|(unsigned long) as;

        mutex_unlock(&c->btree_interior_update_lock);

        btree_update_will_add_key(as, &b->key);
}

/*
 * returns true if @b was a new node
 */
static void btree_update_drop_new_node(struct bch_fs *c, struct btree *b)
{
        struct btree_update *as;
        unsigned long v;
        unsigned i;

        mutex_lock(&c->btree_interior_update_lock);
        /*
         * When b->will_make_reachable != 0, it owns a ref on as->cl that's
         * dropped when it gets written by bch2_btree_complete_write - the
         * xchg() is for synchronization with bch2_btree_complete_write:
         */
        v = xchg(&b->will_make_reachable, 0);
        as = (struct btree_update *) (v & ~1UL);

        if (!as) {
                mutex_unlock(&c->btree_interior_update_lock);
                return;
        }

        for (i = 0; i < as->nr_new_nodes; i++)
                if (as->new_nodes[i] == b)
                        goto found;

        BUG();
found:
        array_remove_item(as->new_nodes, as->nr_new_nodes, i);
        mutex_unlock(&c->btree_interior_update_lock);

        if (v & 1)
                closure_put(&as->cl);
}

void bch2_btree_update_get_open_buckets(struct btree_update *as, struct btree *b)
{
        while (b->ob.nr)
                as->open_buckets[as->nr_open_buckets++] =
                        b->ob.v[--b->ob.nr];
}

/*
 * @b is being split/rewritten: it may have pointers to not-yet-written btree
 * nodes and thus outstanding btree_updates - redirect @b's
 * btree_updates to point to this btree_update:
 */
void bch2_btree_interior_update_will_free_node(struct btree_update *as,
                                               struct btree *b)
{
        struct bch_fs *c = as->c;
        struct btree_update *p, *n;
        struct btree_write *w;

        set_btree_node_dying(b);

        if (btree_node_fake(b))
                return;

        mutex_lock(&c->btree_interior_update_lock);

        /*
         * Does this node have any btree_update operations preventing
         * it from being written?
         *
         * If so, redirect them to point to this btree_update: we can
         * write out our new nodes, but we won't make them visible until those
         * operations complete
         */
        list_for_each_entry_safe(p, n, &b->write_blocked, write_blocked_list) {
                list_del_init(&p->write_blocked_list);
                btree_update_reparent(as, p);

                /*
                 * for flush_held_btree_writes() waiting on updates to flush or
                 * nodes to be writeable:
                 */
                closure_wake_up(&c->btree_interior_update_wait);
        }

        clear_btree_node_dirty(b);
        clear_btree_node_need_write(b);

        /*
         * Does this node have unwritten data that has a pin on the journal?
         *
         * If so, transfer that pin to the btree_update operation -
         * note that if we're freeing multiple nodes, we only need to keep the
         * oldest pin of any of the nodes we're freeing. We'll release the pin
         * when the new nodes are persistent and reachable on disk:
         */
        w = btree_current_write(b);
        bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal, NULL);
        bch2_journal_pin_drop(&c->journal, &w->journal);

        w = btree_prev_write(b);
        bch2_journal_pin_copy(&c->journal, &as->journal, &w->journal, NULL);
        bch2_journal_pin_drop(&c->journal, &w->journal);

        mutex_unlock(&c->btree_interior_update_lock);

        /*
         * Is this a node that isn't reachable on disk yet?
         *
         * Nodes that aren't reachable yet have writes blocked until they're
         * reachable - now that we've cancelled any pending writes and moved
         * things waiting on that write to wait on this update, we can drop this
         * node from the list of nodes that the other update is making
         * reachable, prior to freeing it:
         */
        btree_update_drop_new_node(c, b);

        btree_update_will_delete_key(as, &b->key);
}

void bch2_btree_update_done(struct btree_update *as)
{
        BUG_ON(as->mode == BTREE_INTERIOR_NO_UPDATE);

        bch2_btree_reserve_put(as);

        continue_at(&as->cl, btree_update_set_nodes_written, system_freezable_wq);
}

struct btree_update *
bch2_btree_update_start(struct btree_trans *trans, enum btree_id id,
                        unsigned nr_nodes, unsigned flags,
                        struct closure *cl)
{
        struct bch_fs *c = trans->c;
        struct btree_update *as;
        int disk_res_flags = (flags & BTREE_INSERT_NOFAIL)
                ? BCH_DISK_RESERVATION_NOFAIL : 0;
        int journal_flags = (flags & BTREE_INSERT_JOURNAL_RESERVED)
                ? JOURNAL_RES_GET_RECLAIM : 0;
        int ret = 0;

        /*
         * This check isn't necessary for correctness - it's just to potentially
         * prevent us from doing a lot of work that'll end up being wasted:
         */
        ret = bch2_journal_error(&c->journal);
        if (ret)
                return ERR_PTR(ret);

        as = mempool_alloc(&c->btree_interior_update_pool, GFP_NOIO);
        memset(as, 0, sizeof(*as));
        closure_init(&as->cl, NULL);
        as->c           = c;
        as->mode        = BTREE_INTERIOR_NO_UPDATE;
        as->btree_id    = id;
        INIT_LIST_HEAD(&as->list);
        INIT_LIST_HEAD(&as->unwritten_list);
        INIT_LIST_HEAD(&as->write_blocked_list);
        bch2_keylist_init(&as->old_keys, as->_old_keys);
        bch2_keylist_init(&as->new_keys, as->_new_keys);
        bch2_keylist_init(&as->parent_keys, as->inline_keys);

        ret = bch2_journal_preres_get(&c->journal, &as->journal_preres,
                                      BTREE_UPDATE_JOURNAL_RES,
                                      journal_flags|JOURNAL_RES_GET_NONBLOCK);
        if (ret == -EAGAIN) {
                if (flags & BTREE_INSERT_NOUNLOCK)
                        return ERR_PTR(-EINTR);

                bch2_trans_unlock(trans);

                ret = bch2_journal_preres_get(&c->journal, &as->journal_preres,
                                BTREE_UPDATE_JOURNAL_RES,
                                journal_flags);
                if (ret)
                        return ERR_PTR(ret);

                if (!bch2_trans_relock(trans)) {
                        ret = -EINTR;
                        goto err;
                }
        }

        ret = bch2_disk_reservation_get(c, &as->disk_res,
                        nr_nodes * c->opts.btree_node_size,
                        c->opts.metadata_replicas,
                        disk_res_flags);
        if (ret)
                goto err;

        ret = bch2_btree_reserve_get(as, nr_nodes, flags, cl);
        if (ret)
                goto err;

        mutex_lock(&c->btree_interior_update_lock);
        list_add_tail(&as->list, &c->btree_interior_update_list);
        mutex_unlock(&c->btree_interior_update_lock);

        return as;
err:
        bch2_btree_update_free(as);
        return ERR_PTR(ret);
}

/* Btree root updates: */

static void bch2_btree_set_root_inmem(struct bch_fs *c, struct btree *b)
{
        /* Root nodes cannot be reaped */
        mutex_lock(&c->btree_cache.lock);
        list_del_init(&b->list);
        mutex_unlock(&c->btree_cache.lock);

        mutex_lock(&c->btree_root_lock);
        BUG_ON(btree_node_root(c, b) &&
               (b->c.level < btree_node_root(c, b)->c.level ||
                !btree_node_dying(btree_node_root(c, b))));

        btree_node_root(c, b) = b;
        mutex_unlock(&c->btree_root_lock);

        bch2_recalc_btree_reserve(c);
}

/**
 * bch_btree_set_root - update the root in memory and on disk
 *
 * To ensure forward progress, the current task must not be holding any
 * btree node write locks. However, you must hold an intent lock on the
 * old root.
 *
 * Note: This allocates a journal entry but doesn't add any keys to
 * it.  All the btree roots are part of every journal write, so there
 * is nothing new to be done.  This just guarantees that there is a
 * journal write.
 */
static void bch2_btree_set_root(struct btree_update *as, struct btree *b,
                                struct btree_iter *iter)
{
        struct bch_fs *c = as->c;
        struct btree *old;

        trace_btree_set_root(c, b);
        BUG_ON(!b->written &&
               !test_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags));

        old = btree_node_root(c, b);

        /*
         * Ensure no one is using the old root while we switch to the
         * new root:
         */
        bch2_btree_node_lock_write(old, iter);

        bch2_btree_set_root_inmem(c, b);

        btree_update_updated_root(as, b);

        /*
         * Unlock old root after new root is visible:
         *
         * The new root isn't persistent, but that's ok: we still have
         * an intent lock on the new root, and any updates that would
         * depend on the new root would have to update the new root.
         */
        bch2_btree_node_unlock_write(old, iter);
}

/* Interior node updates: */

static void bch2_insert_fixup_btree_ptr(struct btree_update *as, struct btree *b,
                                        struct btree_iter *iter,
                                        struct bkey_i *insert,
                                        struct btree_node_iter *node_iter)
{
        struct bkey_packed *k;

        BUG_ON(as->journal_u64s + jset_u64s(insert->k.u64s) >
               ARRAY_SIZE(as->journal_entries));

        as->journal_u64s +=
                journal_entry_set((void *) &as->journal_entries[as->journal_u64s],
                                  BCH_JSET_ENTRY_btree_keys,
                                  b->c.btree_id, b->c.level,
                                  insert, insert->k.u64s);

        while ((k = bch2_btree_node_iter_peek_all(node_iter, b)) &&
               bkey_iter_pos_cmp(b, k, &insert->k.p) < 0)
                bch2_btree_node_iter_advance(node_iter, b);

        bch2_btree_bset_insert_key(iter, b, node_iter, insert);
        set_btree_node_dirty(b);
        set_btree_node_need_write(b);
}

/*
 * Move keys from n1 (original replacement node, now lower node) to n2 (higher
 * node)
 */
static struct btree *__btree_split_node(struct btree_update *as,
                                        struct btree *n1,
                                        struct btree_iter *iter)
{
        size_t nr_packed = 0, nr_unpacked = 0;
        struct btree *n2;
        struct bset *set1, *set2;
        struct bkey_packed *k, *prev = NULL;

        n2 = bch2_btree_node_alloc(as, n1->c.level);
        bch2_btree_update_add_new_node(as, n2);

        n2->data->max_key       = n1->data->max_key;
        n2->data->format        = n1->format;
        SET_BTREE_NODE_SEQ(n2->data, BTREE_NODE_SEQ(n1->data));
        n2->key.k.p = n1->key.k.p;

        btree_node_set_format(n2, n2->data->format);

        set1 = btree_bset_first(n1);
        set2 = btree_bset_first(n2);

        /*
         * Has to be a linear search because we don't have an auxiliary
         * search tree yet
         */
        k = set1->start;
        while (1) {
                struct bkey_packed *n = bkey_next_skip_noops(k, vstruct_last(set1));

                if (n == vstruct_last(set1))
                        break;
                if (k->_data - set1->_data >= (le16_to_cpu(set1->u64s) * 3) / 5)
                        break;

                if (bkey_packed(k))
                        nr_packed++;
                else
                        nr_unpacked++;

                prev = k;
                k = n;
        }

        BUG_ON(!prev);

        btree_set_max(n1, bkey_unpack_pos(n1, prev));
        btree_set_min(n2, bkey_successor(n1->key.k.p));

        set2->u64s = cpu_to_le16((u64 *) vstruct_end(set1) - (u64 *) k);
        set1->u64s = cpu_to_le16(le16_to_cpu(set1->u64s) - le16_to_cpu(set2->u64s));

        set_btree_bset_end(n1, n1->set);
        set_btree_bset_end(n2, n2->set);

        n2->nr.live_u64s        = le16_to_cpu(set2->u64s);
        n2->nr.bset_u64s[0]     = le16_to_cpu(set2->u64s);
        n2->nr.packed_keys      = n1->nr.packed_keys - nr_packed;
        n2->nr.unpacked_keys    = n1->nr.unpacked_keys - nr_unpacked;

        n1->nr.live_u64s        = le16_to_cpu(set1->u64s);
        n1->nr.bset_u64s[0]     = le16_to_cpu(set1->u64s);
        n1->nr.packed_keys      = nr_packed;
        n1->nr.unpacked_keys    = nr_unpacked;

        BUG_ON(!set1->u64s);
        BUG_ON(!set2->u64s);

        memcpy_u64s(set2->start,
                    vstruct_end(set1),
                    le16_to_cpu(set2->u64s));

        btree_node_reset_sib_u64s(n1);
        btree_node_reset_sib_u64s(n2);

        bch2_verify_btree_nr_keys(n1);
        bch2_verify_btree_nr_keys(n2);

        if (n1->c.level) {
                btree_node_interior_verify(as->c, n1);
                btree_node_interior_verify(as->c, n2);
        }

        return n2;
}

/*
 * For updates to interior nodes, we've got to do the insert before we split
 * because the stuff we're inserting has to be inserted atomically. Post split,
 * the keys might have to go in different nodes and the split would no longer be
 * atomic.
 *
 * Worse, if the insert is from btree node coalescing, if we do the insert after
 * we do the split (and pick the pivot) - the pivot we pick might be between
 * nodes that were coalesced, and thus in the middle of a child node post
 * coalescing:
 */
static void btree_split_insert_keys(struct btree_update *as, struct btree *b,
                                    struct btree_iter *iter,
                                    struct keylist *keys)
{
        struct btree_node_iter node_iter;
        struct bkey_i *k = bch2_keylist_front(keys);
        struct bkey_packed *src, *dst, *n;
        struct bset *i;

        BUG_ON(btree_node_type(b) != BKEY_TYPE_BTREE);

        bch2_btree_node_iter_init(&node_iter, b, &k->k.p);

        while (!bch2_keylist_empty(keys)) {
                k = bch2_keylist_front(keys);

                bch2_insert_fixup_btree_ptr(as, b, iter, k, &node_iter);
                bch2_keylist_pop_front(keys);
        }

        /*
         * We can't tolerate whiteouts here - with whiteouts there can be
         * duplicate keys, and it would be rather bad if we picked a duplicate
         * for the pivot:
         */
        i = btree_bset_first(b);
        src = dst = i->start;
        while (src != vstruct_last(i)) {
                n = bkey_next_skip_noops(src, vstruct_last(i));
                if (!bkey_deleted(src)) {
                        memmove_u64s_down(dst, src, src->u64s);
                        dst = bkey_next(dst);
                }
                src = n;
        }

        i->u64s = cpu_to_le16((u64 *) dst - i->_data);
        set_btree_bset_end(b, b->set);

        BUG_ON(b->nsets != 1 ||
               b->nr.live_u64s != le16_to_cpu(btree_bset_first(b)->u64s));

        btree_node_interior_verify(as->c, b);
}

static void btree_split(struct btree_update *as, struct btree *b,
                        struct btree_iter *iter, struct keylist *keys,
                        unsigned flags)
{
        struct bch_fs *c = as->c;
        struct btree *parent = btree_node_parent(iter, b);
        struct btree *n1, *n2 = NULL, *n3 = NULL;
        u64 start_time = local_clock();

        BUG_ON(!parent && (b != btree_node_root(c, b)));
        BUG_ON(!btree_node_intent_locked(iter, btree_node_root(c, b)->c.level));

        bch2_btree_interior_update_will_free_node(as, b);

        n1 = bch2_btree_node_alloc_replacement(as, b);
        bch2_btree_update_add_new_node(as, n1);

        if (keys)
                btree_split_insert_keys(as, n1, iter, keys);

        if (bset_u64s(&n1->set[0]) > BTREE_SPLIT_THRESHOLD(c)) {
                trace_btree_split(c, b);

                n2 = __btree_split_node(as, n1, iter);

                bch2_btree_build_aux_trees(n2);
                bch2_btree_build_aux_trees(n1);
                six_unlock_write(&n2->c.lock);
                six_unlock_write(&n1->c.lock);

                bch2_btree_node_write(c, n2, SIX_LOCK_intent);

                /*
                 * Note that on recursive parent_keys == keys, so we
                 * can't start adding new keys to parent_keys before emptying it
                 * out (which we did with btree_split_insert_keys() above)
                 */
                bch2_keylist_add(&as->parent_keys, &n1->key);
                bch2_keylist_add(&as->parent_keys, &n2->key);

                if (!parent) {
                        /* Depth increases, make a new root */
                        n3 = __btree_root_alloc(as, b->c.level + 1);

                        n3->sib_u64s[0] = U16_MAX;
                        n3->sib_u64s[1] = U16_MAX;

                        btree_split_insert_keys(as, n3, iter, &as->parent_keys);

                        bch2_btree_node_write(c, n3, SIX_LOCK_intent);
                }
        } else {
                trace_btree_compact(c, b);

                bch2_btree_build_aux_trees(n1);
                six_unlock_write(&n1->c.lock);

                if (parent)
                        bch2_keylist_add(&as->parent_keys, &n1->key);
        }

        bch2_btree_node_write(c, n1, SIX_LOCK_intent);

        /* New nodes all written, now make them visible: */

        if (parent) {
                /* Split a non root node */
                bch2_btree_insert_node(as, parent, iter, &as->parent_keys, flags);
        } else if (n3) {
                bch2_btree_set_root(as, n3, iter);
        } else {
                /* Root filled up but didn't need to be split */
                bch2_btree_set_root(as, n1, iter);
        }

        bch2_btree_update_get_open_buckets(as, n1);
        if (n2)
                bch2_btree_update_get_open_buckets(as, n2);
        if (n3)
                bch2_btree_update_get_open_buckets(as, n3);

        /* Successful split, update the iterator to point to the new nodes: */

        six_lock_increment(&b->c.lock, SIX_LOCK_intent);
        bch2_btree_iter_node_drop(iter, b);
        if (n3)
                bch2_btree_iter_node_replace(iter, n3);
        if (n2)
                bch2_btree_iter_node_replace(iter, n2);
        bch2_btree_iter_node_replace(iter, n1);

        /*
         * The old node must be freed (in memory) _before_ unlocking the new
         * nodes - else another thread could re-acquire a read lock on the old
         * node after another thread has locked and updated the new node, thus
         * seeing stale data:
         */
        bch2_btree_node_free_inmem(c, b, iter);

        if (n3)
                six_unlock_intent(&n3->c.lock);
        if (n2)
                six_unlock_intent(&n2->c.lock);
        six_unlock_intent(&n1->c.lock);

        bch2_btree_trans_verify_locks(iter->trans);

        bch2_time_stats_update(&c->times[BCH_TIME_btree_node_split],
                               start_time);
}

static void
bch2_btree_insert_keys_interior(struct btree_update *as, struct btree *b,
                                struct btree_iter *iter, struct keylist *keys)
{
        struct btree_iter *linked;
        struct btree_node_iter node_iter;
        struct bkey_i *insert = bch2_keylist_front(keys);
        struct bkey_packed *k;

        /* Don't screw up @iter's position: */
        node_iter = iter->l[b->c.level].iter;

        /*
         * btree_split(), btree_gc_coalesce() will insert keys before
         * the iterator's current position - they know the keys go in
         * the node the iterator points to:
         */
        while ((k = bch2_btree_node_iter_prev_all(&node_iter, b)) &&
               (bkey_cmp_packed(b, k, &insert->k) >= 0))
                ;

        for_each_keylist_key(keys, insert)
                bch2_insert_fixup_btree_ptr(as, b, iter, insert, &node_iter);

        btree_update_updated_node(as, b);

        trans_for_each_iter_with_node(iter->trans, b, linked)
                bch2_btree_node_iter_peek(&linked->l[b->c.level].iter, b);

        bch2_btree_trans_verify_iters(iter->trans, b);
}

/**
 * bch_btree_insert_node - insert bkeys into a given btree node
 *
 * @iter:               btree iterator
 * @keys:               list of keys to insert
 * @hook:               insert callback
 * @persistent:         if not null, @persistent will wait on journal write
 *
 * Inserts as many keys as it can into a given btree node, splitting it if full.
 * If a split occurred, this function will return early. This can only happen
 * for leaf nodes -- inserts into interior nodes have to be atomic.
 */
void bch2_btree_insert_node(struct btree_update *as, struct btree *b,
                            struct btree_iter *iter, struct keylist *keys,
                            unsigned flags)
{
        struct bch_fs *c = as->c;
        int old_u64s = le16_to_cpu(btree_bset_last(b)->u64s);
        int old_live_u64s = b->nr.live_u64s;
        int live_u64s_added, u64s_added;

        BUG_ON(!btree_node_intent_locked(iter, btree_node_root(c, b)->c.level));
        BUG_ON(!b->c.level);
        BUG_ON(!as || as->b);
        bch2_verify_keylist_sorted(keys);

        if (as->must_rewrite)
                goto split;

        bch2_btree_node_lock_for_insert(c, b, iter);

        if (!bch2_btree_node_insert_fits(c, b, bch2_keylist_u64s(keys))) {
                bch2_btree_node_unlock_write(b, iter);
                goto split;
        }

        bch2_btree_insert_keys_interior(as, b, iter, keys);

        live_u64s_added = (int) b->nr.live_u64s - old_live_u64s;
        u64s_added = (int) le16_to_cpu(btree_bset_last(b)->u64s) - old_u64s;

        if (b->sib_u64s[0] != U16_MAX && live_u64s_added < 0)
                b->sib_u64s[0] = max(0, (int) b->sib_u64s[0] + live_u64s_added);
        if (b->sib_u64s[1] != U16_MAX && live_u64s_added < 0)
                b->sib_u64s[1] = max(0, (int) b->sib_u64s[1] + live_u64s_added);

        if (u64s_added > live_u64s_added &&
            bch2_maybe_compact_whiteouts(c, b))
                bch2_btree_iter_reinit_node(iter, b);

        bch2_btree_node_unlock_write(b, iter);

        btree_node_interior_verify(c, b);

        /*
         * when called from the btree_split path the new nodes aren't added to
         * the btree iterator yet, so the merge path's unlock/wait/relock dance
         * won't work:
         */
        bch2_foreground_maybe_merge(c, iter, b->c.level,
                                    flags|BTREE_INSERT_NOUNLOCK);
        return;
split:
        btree_split(as, b, iter, keys, flags);
}

int bch2_btree_split_leaf(struct bch_fs *c, struct btree_iter *iter,
                          unsigned flags)
{
        struct btree_trans *trans = iter->trans;
        struct btree *b = iter_l(iter)->b;
        struct btree_update *as;
        struct closure cl;
        int ret = 0;
        struct btree_insert_entry *i;

        /*
         * We already have a disk reservation and open buckets pinned; this
         * allocation must not block:
         */
        trans_for_each_update(trans, i)
                if (btree_node_type_needs_gc(i->iter->btree_id))
                        flags |= BTREE_INSERT_USE_RESERVE;

        closure_init_stack(&cl);

        /* Hack, because gc and splitting nodes doesn't mix yet: */
        if (!(flags & BTREE_INSERT_GC_LOCK_HELD) &&
            !down_read_trylock(&c->gc_lock)) {
                if (flags & BTREE_INSERT_NOUNLOCK) {
                        trace_transaction_restart_ip(trans->ip, _THIS_IP_);
                        return -EINTR;
                }

                bch2_trans_unlock(trans);
                down_read(&c->gc_lock);

                if (!bch2_trans_relock(trans))
                        ret = -EINTR;
        }

        /*
         * XXX: figure out how far we might need to split,
         * instead of locking/reserving all the way to the root:
         */
        if (!bch2_btree_iter_upgrade(iter, U8_MAX)) {
                trace_trans_restart_iter_upgrade(trans->ip);
                ret = -EINTR;
                goto out;
        }

        as = bch2_btree_update_start(trans, iter->btree_id,
                btree_update_reserve_required(c, b), flags,
                !(flags & BTREE_INSERT_NOUNLOCK) ? &cl : NULL);
        if (IS_ERR(as)) {
                ret = PTR_ERR(as);
                if (ret == -EAGAIN) {
                        BUG_ON(flags & BTREE_INSERT_NOUNLOCK);
                        bch2_trans_unlock(trans);
                        ret = -EINTR;

                        trace_transaction_restart_ip(trans->ip, _THIS_IP_);
                }
                goto out;
        }

        btree_split(as, b, iter, NULL, flags);
        bch2_btree_update_done(as);

        /*
         * We haven't successfully inserted yet, so don't downgrade all the way
         * back to read locks;
         */
        __bch2_btree_iter_downgrade(iter, 1);
out:
        if (!(flags & BTREE_INSERT_GC_LOCK_HELD))
                up_read(&c->gc_lock);
        closure_sync(&cl);
        return ret;
}

void __bch2_foreground_maybe_merge(struct bch_fs *c,
                                   struct btree_iter *iter,
                                   unsigned level,
                                   unsigned flags,
                                   enum btree_node_sibling sib)
{
        struct btree_trans *trans = iter->trans;
        struct btree_update *as;
        struct bkey_format_state new_s;
        struct bkey_format new_f;
        struct bkey_i delete;
        struct btree *b, *m, *n, *prev, *next, *parent;
        struct closure cl;
        size_t sib_u64s;
        int ret = 0;

        BUG_ON(!btree_node_locked(iter, level));

        closure_init_stack(&cl);
retry:
        BUG_ON(!btree_node_locked(iter, level));

        b = iter->l[level].b;

        parent = btree_node_parent(iter, b);
        if (!parent)
                goto out;

        if (b->sib_u64s[sib] > BTREE_FOREGROUND_MERGE_THRESHOLD(c))
                goto out;

        /* XXX: can't be holding read locks */
        m = bch2_btree_node_get_sibling(c, iter, b, sib);
        if (IS_ERR(m)) {
                ret = PTR_ERR(m);
                goto err;
        }

        /* NULL means no sibling: */
        if (!m) {
                b->sib_u64s[sib] = U16_MAX;
                goto out;
        }

        if (sib == btree_prev_sib) {
                prev = m;
                next = b;
        } else {
                prev = b;
                next = m;
        }

        bch2_bkey_format_init(&new_s);
        __bch2_btree_calc_format(&new_s, b);
        __bch2_btree_calc_format(&new_s, m);
        new_f = bch2_bkey_format_done(&new_s);

        sib_u64s = btree_node_u64s_with_format(b, &new_f) +
                btree_node_u64s_with_format(m, &new_f);

        if (sib_u64s > BTREE_FOREGROUND_MERGE_HYSTERESIS(c)) {
                sib_u64s -= BTREE_FOREGROUND_MERGE_HYSTERESIS(c);
                sib_u64s /= 2;
                sib_u64s += BTREE_FOREGROUND_MERGE_HYSTERESIS(c);
        }

        sib_u64s = min(sib_u64s, btree_max_u64s(c));
        b->sib_u64s[sib] = sib_u64s;

        if (b->sib_u64s[sib] > BTREE_FOREGROUND_MERGE_THRESHOLD(c)) {
                six_unlock_intent(&m->c.lock);
                goto out;
        }

        /* We're changing btree topology, doesn't mix with gc: */
        if (!(flags & BTREE_INSERT_GC_LOCK_HELD) &&
            !down_read_trylock(&c->gc_lock))
                goto err_cycle_gc_lock;

        if (!bch2_btree_iter_upgrade(iter, U8_MAX)) {
                ret = -EINTR;
                goto err_unlock;
        }

        as = bch2_btree_update_start(trans, iter->btree_id,
                         btree_update_reserve_required(c, parent) + 1,
                         flags|
                         BTREE_INSERT_NOFAIL|
                         BTREE_INSERT_USE_RESERVE,
                         !(flags & BTREE_INSERT_NOUNLOCK) ? &cl : NULL);
        if (IS_ERR(as)) {
                ret = PTR_ERR(as);
                goto err_unlock;
        }

        trace_btree_merge(c, b);

        bch2_btree_interior_update_will_free_node(as, b);
        bch2_btree_interior_update_will_free_node(as, m);

        n = bch2_btree_node_alloc(as, b->c.level);
        bch2_btree_update_add_new_node(as, n);

        btree_set_min(n, prev->data->min_key);
        btree_set_max(n, next->data->max_key);
        n->data->format         = new_f;

        btree_node_set_format(n, new_f);

        bch2_btree_sort_into(c, n, prev);
        bch2_btree_sort_into(c, n, next);

        bch2_btree_build_aux_trees(n);
        six_unlock_write(&n->c.lock);

        bkey_init(&delete.k);
        delete.k.p = prev->key.k.p;
        bch2_keylist_add(&as->parent_keys, &delete);
        bch2_keylist_add(&as->parent_keys, &n->key);

        bch2_btree_node_write(c, n, SIX_LOCK_intent);

        bch2_btree_insert_node(as, parent, iter, &as->parent_keys, flags);

        bch2_btree_update_get_open_buckets(as, n);

        six_lock_increment(&b->c.lock, SIX_LOCK_intent);
        bch2_btree_iter_node_drop(iter, b);
        bch2_btree_iter_node_drop(iter, m);

        bch2_btree_iter_node_replace(iter, n);

        bch2_btree_trans_verify_iters(trans, n);

        bch2_btree_node_free_inmem(c, b, iter);
        bch2_btree_node_free_inmem(c, m, iter);

        six_unlock_intent(&n->c.lock);

        bch2_btree_update_done(as);

        if (!(flags & BTREE_INSERT_GC_LOCK_HELD))
                up_read(&c->gc_lock);
out:
        bch2_btree_trans_verify_locks(trans);

        /*
         * Don't downgrade locks here: we're called after successful insert,
         * and the caller will downgrade locks after a successful insert
         * anyways (in case e.g. a split was required first)
         *
         * And we're also called when inserting into interior nodes in the
         * split path, and downgrading to read locks in there is potentially
         * confusing:
         */
        closure_sync(&cl);
        return;

err_cycle_gc_lock:
        six_unlock_intent(&m->c.lock);

        if (flags & BTREE_INSERT_NOUNLOCK)
                goto out;

        bch2_trans_unlock(trans);

        down_read(&c->gc_lock);
        up_read(&c->gc_lock);
        ret = -EINTR;
        goto err;

err_unlock:
        six_unlock_intent(&m->c.lock);
        if (!(flags & BTREE_INSERT_GC_LOCK_HELD))
                up_read(&c->gc_lock);
err:
        BUG_ON(ret == -EAGAIN && (flags & BTREE_INSERT_NOUNLOCK));

        if ((ret == -EAGAIN || ret == -EINTR) &&
            !(flags & BTREE_INSERT_NOUNLOCK)) {
                bch2_trans_unlock(trans);
                closure_sync(&cl);
                ret = bch2_btree_iter_traverse(iter);
                if (ret)
                        goto out;

                goto retry;
        }

        goto out;
}

static int __btree_node_rewrite(struct bch_fs *c, struct btree_iter *iter,
                                struct btree *b, unsigned flags,
                                struct closure *cl)
{
        struct btree *n, *parent = btree_node_parent(iter, b);
        struct btree_update *as;

        as = bch2_btree_update_start(iter->trans, iter->btree_id,
                (parent
                 ? btree_update_reserve_required(c, parent)
                 : 0) + 1,
                flags, cl);
        if (IS_ERR(as)) {
                trace_btree_gc_rewrite_node_fail(c, b);
                return PTR_ERR(as);
        }

        bch2_btree_interior_update_will_free_node(as, b);

        n = bch2_btree_node_alloc_replacement(as, b);
        bch2_btree_update_add_new_node(as, n);

        bch2_btree_build_aux_trees(n);
        six_unlock_write(&n->c.lock);

        trace_btree_gc_rewrite_node(c, b);

        bch2_btree_node_write(c, n, SIX_LOCK_intent);

        if (parent) {
                bch2_keylist_add(&as->parent_keys, &n->key);
                bch2_btree_insert_node(as, parent, iter, &as->parent_keys, flags);
        } else {
                bch2_btree_set_root(as, n, iter);
        }

        bch2_btree_update_get_open_buckets(as, n);

        six_lock_increment(&b->c.lock, SIX_LOCK_intent);
        bch2_btree_iter_node_drop(iter, b);
        bch2_btree_iter_node_replace(iter, n);
        bch2_btree_node_free_inmem(c, b, iter);
        six_unlock_intent(&n->c.lock);

        bch2_btree_update_done(as);
        return 0;
}

/**
 * bch_btree_node_rewrite - Rewrite/move a btree node
 *
 * Returns 0 on success, -EINTR or -EAGAIN on failure (i.e.
 * btree_check_reserve() has to wait)
 */
int bch2_btree_node_rewrite(struct bch_fs *c, struct btree_iter *iter,
                            __le64 seq, unsigned flags)
{
        struct btree_trans *trans = iter->trans;
        struct closure cl;
        struct btree *b;
        int ret;

        flags |= BTREE_INSERT_NOFAIL;

        closure_init_stack(&cl);

        bch2_btree_iter_upgrade(iter, U8_MAX);

        if (!(flags & BTREE_INSERT_GC_LOCK_HELD)) {
                if (!down_read_trylock(&c->gc_lock)) {
                        bch2_trans_unlock(trans);
                        down_read(&c->gc_lock);
                }
        }

        while (1) {
                ret = bch2_btree_iter_traverse(iter);
                if (ret)
                        break;

                b = bch2_btree_iter_peek_node(iter);
                if (!b || b->data->keys.seq != seq)
                        break;

                ret = __btree_node_rewrite(c, iter, b, flags, &cl);
                if (ret != -EAGAIN &&
                    ret != -EINTR)
                        break;

                bch2_trans_unlock(trans);
                closure_sync(&cl);
        }

        bch2_btree_iter_downgrade(iter);

        if (!(flags & BTREE_INSERT_GC_LOCK_HELD))
                up_read(&c->gc_lock);

        closure_sync(&cl);
        return ret;
}

static void __bch2_btree_node_update_key(struct bch_fs *c,
                                         struct btree_update *as,
                                         struct btree_iter *iter,
                                         struct btree *b, struct btree *new_hash,
                                         struct bkey_i *new_key)
{
        struct btree *parent;
        int ret;

        btree_update_will_delete_key(as, &b->key);
        btree_update_will_add_key(as, new_key);

        parent = btree_node_parent(iter, b);
        if (parent) {
                if (new_hash) {
                        bkey_copy(&new_hash->key, new_key);
                        ret = bch2_btree_node_hash_insert(&c->btree_cache,
                                        new_hash, b->c.level, b->c.btree_id);
                        BUG_ON(ret);
                }

                bch2_keylist_add(&as->parent_keys, new_key);
                bch2_btree_insert_node(as, parent, iter, &as->parent_keys, 0);

                if (new_hash) {
                        mutex_lock(&c->btree_cache.lock);
                        bch2_btree_node_hash_remove(&c->btree_cache, new_hash);

                        bch2_btree_node_hash_remove(&c->btree_cache, b);

                        bkey_copy(&b->key, new_key);
                        ret = __bch2_btree_node_hash_insert(&c->btree_cache, b);
                        BUG_ON(ret);
                        mutex_unlock(&c->btree_cache.lock);
                } else {
                        bkey_copy(&b->key, new_key);
                }
        } else {
                BUG_ON(btree_node_root(c, b) != b);

                bch2_btree_node_lock_write(b, iter);
                bkey_copy(&b->key, new_key);

                if (btree_ptr_hash_val(&b->key) != b->hash_val) {
                        mutex_lock(&c->btree_cache.lock);
                        bch2_btree_node_hash_remove(&c->btree_cache, b);

                        ret = __bch2_btree_node_hash_insert(&c->btree_cache, b);
                        BUG_ON(ret);
                        mutex_unlock(&c->btree_cache.lock);
                }

                btree_update_updated_root(as, b);
                bch2_btree_node_unlock_write(b, iter);
        }

        bch2_btree_update_done(as);
}

int bch2_btree_node_update_key(struct bch_fs *c, struct btree_iter *iter,
                               struct btree *b,
                               struct bkey_i *new_key)
{
        struct btree *parent = btree_node_parent(iter, b);
        struct btree_update *as = NULL;
        struct btree *new_hash = NULL;
        struct closure cl;
        int ret;

        closure_init_stack(&cl);

        if (!bch2_btree_iter_upgrade(iter, U8_MAX))
                return -EINTR;

        if (!down_read_trylock(&c->gc_lock)) {
                bch2_trans_unlock(iter->trans);
                down_read(&c->gc_lock);

                if (!bch2_trans_relock(iter->trans)) {
                        ret = -EINTR;
                        goto err;
                }
        }

        /*
         * check btree_ptr_hash_val() after @b is locked by
         * btree_iter_traverse():
         */
        if (btree_ptr_hash_val(new_key) != b->hash_val) {
                /* bch2_btree_reserve_get will unlock */
                ret = bch2_btree_cache_cannibalize_lock(c, &cl);
                if (ret) {
                        bch2_trans_unlock(iter->trans);
                        up_read(&c->gc_lock);
                        closure_sync(&cl);
                        down_read(&c->gc_lock);

                        if (!bch2_trans_relock(iter->trans)) {
                                ret = -EINTR;
                                goto err;
                        }
                }

                new_hash = bch2_btree_node_mem_alloc(c);
        }
retry:
        as = bch2_btree_update_start(iter->trans, iter->btree_id,
                parent ? btree_update_reserve_required(c, parent) : 0,
                BTREE_INSERT_NOFAIL|
                BTREE_INSERT_USE_RESERVE|
                BTREE_INSERT_USE_ALLOC_RESERVE,
                &cl);

        if (IS_ERR(as)) {
                ret = PTR_ERR(as);
                if (ret == -EAGAIN)
                        ret = -EINTR;

                if (ret == -EINTR) {
                        bch2_trans_unlock(iter->trans);
                        up_read(&c->gc_lock);
                        closure_sync(&cl);
                        down_read(&c->gc_lock);

                        if (bch2_trans_relock(iter->trans))
                                goto retry;
                }

                goto err;
        }

        ret = bch2_mark_bkey_replicas(c, bkey_i_to_s_c(new_key));
        if (ret)
                goto err_free_update;

        __bch2_btree_node_update_key(c, as, iter, b, new_hash, new_key);

        bch2_btree_iter_downgrade(iter);
err:
        if (new_hash) {
                mutex_lock(&c->btree_cache.lock);
                list_move(&new_hash->list, &c->btree_cache.freeable);
                mutex_unlock(&c->btree_cache.lock);

                six_unlock_write(&new_hash->c.lock);
                six_unlock_intent(&new_hash->c.lock);
        }
        up_read(&c->gc_lock);
        closure_sync(&cl);
        return ret;
err_free_update:
        bch2_btree_update_free(as);
        goto err;
}

/* Init code: */

/*
 * Only for filesystem bringup, when first reading the btree roots or allocating
 * btree roots when initializing a new filesystem:
 */
void bch2_btree_set_root_for_read(struct bch_fs *c, struct btree *b)
{
        BUG_ON(btree_node_root(c, b));

        bch2_btree_set_root_inmem(c, b);
}

void bch2_btree_root_alloc(struct bch_fs *c, enum btree_id id)
{
        struct closure cl;
        struct btree *b;
        int ret;

        closure_init_stack(&cl);

        do {
                ret = bch2_btree_cache_cannibalize_lock(c, &cl);
                closure_sync(&cl);
        } while (ret);

        b = bch2_btree_node_mem_alloc(c);
        bch2_btree_cache_cannibalize_unlock(c);

        set_btree_node_fake(b);
        set_btree_node_need_rewrite(b);
        b->c.level      = 0;
        b->c.btree_id   = id;

        bkey_btree_ptr_init(&b->key);
        b->key.k.p = POS_MAX;
        *((u64 *) bkey_i_to_btree_ptr(&b->key)->v.start) = U64_MAX - id;

        bch2_bset_init_first(b, &b->data->keys);
        bch2_btree_build_aux_trees(b);

        b->data->flags = 0;
        btree_set_min(b, POS_MIN);
        btree_set_max(b, POS_MAX);
        b->data->format = bch2_btree_calc_format(b);
        btree_node_set_format(b, b->data->format);

        ret = bch2_btree_node_hash_insert(&c->btree_cache, b,
                                          b->c.level, b->c.btree_id);
        BUG_ON(ret);

        bch2_btree_set_root_inmem(c, b);

        six_unlock_write(&b->c.lock);
        six_unlock_intent(&b->c.lock);
}

void bch2_btree_updates_to_text(struct printbuf *out, struct bch_fs *c)
{
        struct btree_update *as;

        mutex_lock(&c->btree_interior_update_lock);
        list_for_each_entry(as, &c->btree_interior_update_list, list)
                pr_buf(out, "%p m %u w %u r %u j %llu\n",
                       as,
                       as->mode,
                       as->nodes_written,
                       atomic_read(&as->cl.remaining) & CLOSURE_REMAINING_MASK,
                       as->journal.seq);
        mutex_unlock(&c->btree_interior_update_lock);
}

size_t bch2_btree_interior_updates_nr_pending(struct bch_fs *c)
{
        size_t ret = 0;
        struct list_head *i;

        mutex_lock(&c->btree_interior_update_lock);
        list_for_each(i, &c->btree_interior_update_list)
                ret++;
        mutex_unlock(&c->btree_interior_update_lock);

        return ret;
}

void bch2_journal_entries_to_btree_roots(struct bch_fs *c, struct jset *jset)
{
        struct btree_root *r;
        struct jset_entry *entry;

        mutex_lock(&c->btree_root_lock);

        vstruct_for_each(jset, entry)
                if (entry->type == BCH_JSET_ENTRY_btree_root) {
                        r = &c->btree_roots[entry->btree_id];
                        r->level = entry->level;
                        r->alive = true;
                        bkey_copy(&r->key, &entry->start[0]);
                }

        mutex_unlock(&c->btree_root_lock);
}

struct jset_entry *
bch2_btree_roots_to_journal_entries(struct bch_fs *c,
                                    struct jset_entry *start,
                                    struct jset_entry *end)
{
        struct jset_entry *entry;
        unsigned long have = 0;
        unsigned i;

        for (entry = start; entry < end; entry = vstruct_next(entry))
                if (entry->type == BCH_JSET_ENTRY_btree_root)
                        __set_bit(entry->btree_id, &have);

        mutex_lock(&c->btree_root_lock);

        for (i = 0; i < BTREE_ID_NR; i++)
                if (c->btree_roots[i].alive && !test_bit(i, &have)) {
                        journal_entry_set(end,
                                          BCH_JSET_ENTRY_btree_root,
                                          i, c->btree_roots[i].level,
                                          &c->btree_roots[i].key,
                                          c->btree_roots[i].key.u64s);
                        end = vstruct_next(end);
                }

        mutex_unlock(&c->btree_root_lock);

        return end;
}

void bch2_fs_btree_interior_update_exit(struct bch_fs *c)
{
        if (c->btree_interior_update_worker)
                destroy_workqueue(c->btree_interior_update_worker);
        mempool_exit(&c->btree_interior_update_pool);
}

int bch2_fs_btree_interior_update_init(struct bch_fs *c)
{
        mutex_init(&c->btree_reserve_cache_lock);
        INIT_LIST_HEAD(&c->btree_interior_update_list);
        INIT_LIST_HEAD(&c->btree_interior_updates_unwritten);
        mutex_init(&c->btree_interior_update_lock);
        INIT_WORK(&c->btree_interior_update_work, btree_interior_update_work);

        c->btree_interior_update_worker =
                alloc_workqueue("btree_update", WQ_UNBOUND|WQ_MEM_RECLAIM, 1);
        if (!c->btree_interior_update_worker)
                return -ENOMEM;

        return mempool_init_kmalloc_pool(&c->btree_interior_update_pool, 1,
                                         sizeof(struct btree_update));
}