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

#include "bcachefs.h"
#include "alloc.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>

static void btree_node_will_make_reachable(struct btree_update *,
                                           struct btree *);
static void btree_update_drop_new_node(struct bch_fs *, struct btree *);
static void bch2_btree_set_root_ondisk(struct bch_fs *, struct btree *, int);

/* Debug code: */

static void btree_node_interior_verify(struct btree *b)
{
        struct btree_node_iter iter;
        struct bkey_packed *k;

        BUG_ON(!b->level);

        bch2_btree_node_iter_init(&iter, b, b->key.k.p, false, false);
#if 1
        BUG_ON(!(k = bch2_btree_node_iter_peek(&iter, b)) ||
               bkey_cmp_left_packed(b, k, &b->key.k.p));

        BUG_ON((bch2_btree_node_iter_advance(&iter, b),
                !bch2_btree_node_iter_end(&iter)));
#else
        const char *msg;

        msg = "not found";
        k = bch2_btree_node_iter_peek(&iter, b);
        if (!k)
                goto err;

        msg = "isn't what it should be";
        if (bkey_cmp_left_packed(b, k, &b->key.k.p))
                goto err;

        bch2_btree_node_iter_advance(&iter, b);

        msg = "isn't last key";
        if (!bch2_btree_node_iter_end(&iter))
                goto err;
        return;
err:
        bch2_dump_btree_node(b);
        printk(KERN_ERR "last key %llu:%llu %s\n", b->key.k.p.inode,
               b->key.k.p.offset, msg);
        BUG();
#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)
                for (k = btree_bkey_first(b, t);
                     k != btree_bkey_last(b, t);
                     k = bkey_next(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 bool btree_key_matches(struct bch_fs *c,
                              struct bkey_s_c_extent l,
                              struct bkey_s_c_extent r)
{
        const struct bch_extent_ptr *ptr1, *ptr2;

        extent_for_each_ptr(l, ptr1)
                extent_for_each_ptr(r, ptr2)
                        if (ptr1->dev == ptr2->dev &&
                            ptr1->gen == ptr2->gen &&
                            ptr1->offset == ptr2->offset)
                                return true;

        return false;
}

/*
 * We're doing the index update that makes @b unreachable, update stuff to
 * reflect that:
 *
 * Must be called _before_ btree_update_updated_root() or
 * btree_update_updated_node:
 */
static void bch2_btree_node_free_index(struct btree_update *as, struct btree *b,
                                       struct bkey_s_c k,
                                       struct bch_fs_usage *stats)
{
        struct bch_fs *c = as->c;
        struct pending_btree_node_free *d;
        unsigned replicas;

        /*
         * btree_update lock is only needed here to avoid racing with
         * gc:
         */
        mutex_lock(&c->btree_interior_update_lock);

        for (d = as->pending; d < as->pending + as->nr_pending; d++)
                if (!bkey_cmp(k.k->p, d->key.k.p) &&
                    btree_key_matches(c, bkey_s_c_to_extent(k),
                                      bkey_i_to_s_c_extent(&d->key)))
                        goto found;
        BUG();
found:
        BUG_ON(d->index_update_done);
        d->index_update_done = true;

        /*
         * Btree nodes are accounted as freed in bch_alloc_stats when they're
         * freed from the index:
         */
        replicas = bch2_extent_nr_dirty_ptrs(k);
        if (replicas)
                stats->s[replicas - 1].data[S_META] -= c->opts.btree_node_size;

        /*
         * We're dropping @k from the btree, but it's still live until the
         * index update is persistent so we need to keep a reference around for
         * mark and sweep to find - that's primarily what the
         * btree_node_pending_free list is for.
         *
         * So here (when we set index_update_done = true), we're moving an
         * existing reference to a different part of the larger "gc keyspace" -
         * and the new position comes after the old position, since GC marks
         * the pending free list after it walks the btree.
         *
         * If we move the reference while mark and sweep is _between_ the old
         * and the new position, mark and sweep will see the reference twice
         * and it'll get double accounted - so check for that here and subtract
         * to cancel out one of mark and sweep's markings if necessary:
         */

        /*
         * bch2_mark_key() compares the current gc pos to the pos we're
         * moving this reference from, hence one comparison here:
         */
        if (gc_pos_cmp(c->gc_pos, gc_phase(GC_PHASE_PENDING_DELETE)) < 0) {
                struct bch_fs_usage tmp = { 0 };

                bch2_mark_key(c, bkey_i_to_s_c(&d->key),
                             -c->opts.btree_node_size, true, b
                             ? gc_pos_btree_node(b)
                             : gc_pos_btree_root(as->btree_id),
                             &tmp, 0, 0);
                /*
                 * Don't apply tmp - pending deletes aren't tracked in
                 * bch_alloc_stats:
                 */
        }

        mutex_unlock(&c->btree_interior_update_lock);
}

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

        six_lock_write(&b->lock);

        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);

        /*
         * By using six_unlock_write() directly instead of
         * bch2_btree_node_unlock_write(), we don't update the iterator's
         * sequence numbers and cause future bch2_btree_node_relock() calls to
         * fail:
         */
        six_unlock_write(&b->lock);
}

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

        btree_update_drop_new_node(c, b);

        b->ob.nr = 0;

        clear_btree_node_dirty(b);

        __btree_node_free(c, b, NULL);

        bch2_open_bucket_put_refs(c, &ob.nr, ob.refs);
}

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

        bch2_btree_iter_node_drop_linked(iter, b);

        __btree_node_free(c, b, iter);

        bch2_btree_iter_node_drop(iter, b);
}

static void bch2_btree_node_free_ondisk(struct bch_fs *c,
                                        struct pending_btree_node_free *pending)
{
        struct bch_fs_usage stats = { 0 };

        BUG_ON(!pending->index_update_done);

        bch2_mark_key(c, bkey_i_to_s_c(&pending->key),
                     -c->opts.btree_node_size, true,
                     gc_phase(GC_PHASE_PENDING_DELETE),
                     &stats, 0, 0);
        /*
         * Don't apply stats - pending deletes aren't tracked in
         * bch_alloc_stats:
         */
}

void bch2_btree_open_bucket_put(struct bch_fs *c, struct btree *b)
{
        bch2_open_bucket_put_refs(c, &b->ob.nr, b->ob.refs);
}

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 bkey_i_extent *e;
        struct btree_ob_ref ob;
        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,
                                      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;

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

                bch2_alloc_sectors_done(c, wp);
                goto retry;
        }

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

        ob.nr = 0;
        bch2_open_bucket_get(c, wp, &ob.nr, ob.refs);
        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;

        BUG_ON(level >= BTREE_MAX_DEPTH);
        BUG_ON(!as->reserve->nr);

        b = as->reserve->b[--as->reserve->nr];

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

        set_btree_node_accessed(b);
        set_btree_node_dirty(b);

        bch2_bset_init_first(b, &b->data->keys);
        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 = bkey_i_to_extent(&b->key)->v.start->ptr;

        bch2_btree_build_aux_trees(b);

        btree_node_will_make_reachable(as, b);

        trace_btree_node_alloc(c, b);
        return b;
}

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->level);

        n->data->min_key        = b->data->min_key;
        n->data->max_key        = b->data->max_key;
        n->data->format         = format;
        SET_BTREE_NODE_SEQ(n->data, BTREE_NODE_SEQ(b->data) + 1);

        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);

        b->data->min_key = POS_MIN;
        b->data->max_key = POS_MAX;
        b->data->format = bch2_btree_calc_format(b);
        b->key.k.p = POS_MAX;

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

        six_unlock_write(&b->lock);

        return b;
}

static void bch2_btree_reserve_put(struct bch_fs *c, struct btree_reserve *reserve)
{
        bch2_disk_reservation_put(c, &reserve->disk_res);

        mutex_lock(&c->btree_reserve_cache_lock);

        while (reserve->nr) {
                struct btree *b = reserve->b[--reserve->nr];

                six_unlock_write(&b->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_btree_open_bucket_put(c, b);
                }

                __btree_node_free(c, b, NULL);

                six_unlock_intent(&b->lock);
        }

        mutex_unlock(&c->btree_reserve_cache_lock);

        mempool_free(reserve, &c->btree_reserve_pool);
}

static struct btree_reserve *bch2_btree_reserve_get(struct bch_fs *c,
                                                    unsigned nr_nodes,
                                                    unsigned flags,
                                                    struct closure *cl)
{
        struct btree_reserve *reserve;
        struct btree *b;
        struct disk_reservation disk_res = { 0, 0 };
        unsigned sectors = nr_nodes * c->opts.btree_node_size;
        int ret, disk_res_flags = BCH_DISK_RESERVATION_GC_LOCK_HELD;

        if (flags & BTREE_INSERT_NOFAIL)
                disk_res_flags |= BCH_DISK_RESERVATION_NOFAIL;

        /*
         * 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);

        if (bch2_disk_reservation_get(c, &disk_res, sectors,
                                      c->opts.metadata_replicas,
                                      disk_res_flags))
                return ERR_PTR(-ENOSPC);

        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) {
                bch2_disk_reservation_put(c, &disk_res);
                return ERR_PTR(ret);
        }

        reserve = mempool_alloc(&c->btree_reserve_pool, GFP_NOIO);

        reserve->disk_res = disk_res;
        reserve->nr = 0;

        while (reserve->nr < nr_nodes) {
                b = __bch2_btree_node_alloc(c, &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, BCH_DATA_BTREE,
                                              bkey_i_to_s_c(&b->key));
                if (ret)
                        goto err_free;

                reserve->b[reserve->nr++] = b;
        }

        bch2_btree_cache_cannibalize_unlock(c);
        return reserve;
err_free:
        bch2_btree_reserve_put(c, reserve);
        bch2_btree_cache_cannibalize_unlock(c);
        trace_btree_reserve_get_fail(c, nr_nodes, cl);
        return ERR_PTR(ret);
}

/* Asynchronous interior node update machinery */

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

        BUG_ON(as->nr_new_nodes);
        BUG_ON(as->nr_pending);

        if (as->reserve)
                bch2_btree_reserve_put(c, as->reserve);

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

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

        closure_wake_up(&c->btree_interior_update_wait);
        mutex_unlock(&c->btree_interior_update_lock);
}

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

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

        mutex_lock(&c->btree_interior_update_lock);

        while (as->nr_new_nodes) {
                struct btree *b = as->new_nodes[--as->nr_new_nodes];

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

                /*
                 * b->will_make_reachable prevented it from being written, so
                 * write it now if it needs to be written:
                 */
                six_lock_read(&b->lock);
                bch2_btree_node_write_cond(c, b, btree_node_need_write(b));
                six_unlock_read(&b->lock);
                mutex_lock(&c->btree_interior_update_lock);
        }

        while (as->nr_pending)
                bch2_btree_node_free_ondisk(c, &as->pending[--as->nr_pending]);

        mutex_unlock(&c->btree_interior_update_lock);

        closure_wake_up(&as->wait);

        bch2_btree_update_free(as);
}

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

        ret = bch2_journal_open_seq_async(&c->journal, as->journal_seq, cl);
        if (ret < 0)
                goto err;
        if (!ret)
                continue_at(cl, btree_update_wait_on_journal, system_wq);

        bch2_journal_flush_seq_async(&c->journal, as->journal_seq, cl);
err:
        continue_at(cl, btree_update_nodes_reachable, system_wq);
}

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

        /*
         * 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.
         */
retry:
        mutex_lock(&c->btree_interior_update_lock);
        as->nodes_written = true;

        switch (as->mode) {
        case BTREE_INTERIOR_NO_UPDATE:
                BUG();
        case BTREE_INTERIOR_UPDATING_NODE:
                /* The usual case: */
                b = READ_ONCE(as->b);

                if (!six_trylock_read(&b->lock)) {
                        mutex_unlock(&c->btree_interior_update_lock);
                        six_lock_read(&b->lock);
                        six_unlock_read(&b->lock);
                        goto retry;
                }

                BUG_ON(!btree_node_dirty(b));
                closure_wait(&btree_current_write(b)->wait, cl);

                list_del(&as->write_blocked_list);
                mutex_unlock(&c->btree_interior_update_lock);

                /*
                 * b->write_blocked prevented it from being written, so
                 * write it now if it needs to be written:
                 */
                bch2_btree_node_write_cond(c, b, true);
                six_unlock_read(&b->lock);
                break;

        case BTREE_INTERIOR_UPDATING_AS:
                /*
                 * The btree node we originally updated has been freed and is
                 * being rewritten - so we need to write anything here, we just
                 * need to signal to that btree_update that it's ok to make the
                 * new replacement node visible:
                 */
                closure_put(&as->parent_as->cl);

                /*
                 * and then we have to wait on that btree_update to finish:
                 */
                closure_wait(&as->parent_as->wait, cl);
                mutex_unlock(&c->btree_interior_update_lock);
                break;

        case BTREE_INTERIOR_UPDATING_ROOT:
                /* b is the new btree root: */
                b = READ_ONCE(as->b);

                if (!six_trylock_read(&b->lock)) {
                        mutex_unlock(&c->btree_interior_update_lock);
                        six_lock_read(&b->lock);
                        six_unlock_read(&b->lock);
                        goto retry;
                }

                BUG_ON(c->btree_roots[b->btree_id].as != as);
                c->btree_roots[b->btree_id].as = NULL;

                bch2_btree_set_root_ondisk(c, b, WRITE);

                /*
                 * We don't have to wait anything anything here (before
                 * btree_update_nodes_reachable frees the old nodes
                 * ondisk) - we've ensured that the very next journal write will
                 * have the pointer to the new root, and before the allocator
                 * can reuse the old nodes it'll have to do a journal commit:
                 */
                six_unlock_read(&b->lock);
                mutex_unlock(&c->btree_interior_update_lock);

                /*
                 * Bit of funny circularity going on here we have to break:
                 *
                 * We have to drop our journal pin before writing the journal
                 * entry that points to the new btree root: else, we could
                 * deadlock if the journal currently happens to be full.
                 *
                 * This mean we're dropping the journal pin _before_ the new
                 * nodes are technically reachable - but this is safe, because
                 * after the bch2_btree_set_root_ondisk() call above they will
                 * be reachable as of the very next journal write:
                 */
                bch2_journal_pin_drop(&c->journal, &as->journal);

                as->journal_seq = bch2_journal_last_unwritten_seq(&c->journal);

                btree_update_wait_on_journal(cl);
                return;
        }

        continue_at(cl, btree_update_nodes_reachable, system_wq);
}

/*
 * 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);

        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);

        /*
         * In general, when you're staging things in a journal that will later
         * be written elsewhere, and you also want to guarantee ordering: that
         * is, if you have updates a, b, c, after a crash you should never see c
         * and not a or b - there's a problem:
         *
         * If the final destination of the update(s) (i.e. btree node) can be
         * written/flushed _before_ the relevant journal entry - oops, that
         * breaks ordering, since the various leaf nodes can be written in any
         * order.
         *
         * Normally we use bset->journal_seq to deal with this - if during
         * recovery we find a btree node write that's newer than the newest
         * journal entry, we just ignore it - we don't need it, anything we're
         * supposed to have (that we reported as completed via fsync()) will
         * still be in the journal, and as far as the state of the journal is
         * concerned that btree node write never happened.
         *
         * That breaks when we're rewriting/splitting/merging nodes, since we're
         * mixing btree node writes that haven't happened yet with previously
         * written data that has been reported as completed to the journal.
         *
         * Thus, before making the new nodes reachable, we have to wait the
         * newest journal sequence number we have data for to be written (if it
         * hasn't been yet).
         */
        bch2_journal_wait_on_seq(&c->journal, as->journal_seq, &as->cl);
}

static void interior_update_flush(struct journal *j,
                        struct journal_entry_pin *pin, u64 seq)
{
        struct btree_update *as =
                container_of(pin, struct btree_update, journal);

        bch2_journal_flush_seq_async(j, as->journal_seq, NULL);
}

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

        child->b = NULL;
        child->mode = BTREE_INTERIOR_UPDATING_AS;
        child->parent_as = as;
        closure_get(&as->cl);

        /*
         * 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_add_if_older(&c->journal, &child->journal,
                                      &as->journal, interior_update_flush);
        bch2_journal_pin_drop(&c->journal, &child->journal);

        as->journal_seq = max(as->journal_seq, child->journal_seq);
}

static void btree_update_updated_root(struct btree_update *as)
{
        struct bch_fs *c = as->c;
        struct btree_root *r = &c->btree_roots[as->btree_id];

        mutex_lock(&c->btree_interior_update_lock);

        BUG_ON(as->mode != BTREE_INTERIOR_NO_UPDATE);

        /*
         * Old root might not be persistent yet - if so, redirect its
         * btree_update operation to point to us:
         */
        if (r->as)
                btree_update_reparent(as, r->as);

        as->mode = BTREE_INTERIOR_UPDATING_ROOT;
        as->b = r->b;
        r->as = as;

        mutex_unlock(&c->btree_interior_update_lock);

        /*
         * When we're rewriting nodes and updating interior nodes, there's an
         * issue with updates that haven't been written in the journal getting
         * mixed together with older data - see btree_update_updated_node()
         * for the explanation.
         *
         * However, this doesn't affect us when we're writing a new btree root -
         * because to make that new root reachable we have to write out a new
         * journal entry, which must necessarily be newer than as->journal_seq.
         */
}

static void btree_node_will_make_reachable(struct btree_update *as,
                                           struct btree *b)
{
        struct bch_fs *c = as->c;

        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;

        closure_get(&as->cl);
        mutex_unlock(&c->btree_interior_update_lock);
}

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);
        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);
}

static void btree_interior_update_add_node_reference(struct btree_update *as,
                                                     struct btree *b)
{
        struct bch_fs *c = as->c;
        struct pending_btree_node_free *d;

        mutex_lock(&c->btree_interior_update_lock);

        /* Add this node to the list of nodes being freed: */
        BUG_ON(as->nr_pending >= ARRAY_SIZE(as->pending));

        d = &as->pending[as->nr_pending++];
        d->index_update_done    = false;
        d->seq                  = b->data->keys.seq;
        d->btree_id             = b->btree_id;
        d->level                = b->level;
        bkey_copy(&d->key, &b->key);

        mutex_unlock(&c->btree_interior_update_lock);
}

/*
 * @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 closure *cl, *cl_n;
        struct btree_update *p, *n;
        struct btree_write *w;
        struct bset_tree *t;

        set_btree_node_dying(b);

        if (btree_node_fake(b))
                return;

        btree_interior_update_add_node_reference(as, b);

        /*
         * Does this node have data that hasn't been written in the journal?
         *
         * If so, we have to wait for the corresponding journal entry to be
         * written before making the new nodes reachable - we can't just carry
         * over the bset->journal_seq tracking, since we'll be mixing those keys
         * in with keys that aren't in the journal anymore:
         */
        for_each_bset(b, t)
                as->journal_seq = max(as->journal_seq,
                                      le64_to_cpu(bset(b, t)->journal_seq));

        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(&p->write_blocked_list);
                btree_update_reparent(as, p);
        }

        clear_btree_node_dirty(b);
        clear_btree_node_need_write(b);
        w = btree_current_write(b);

        /*
         * Does this node have any btree_update operations waiting on this node
         * to be written?
         *
         * If so, wake them up when this btree_update operation is reachable:
         */
        llist_for_each_entry_safe(cl, cl_n, llist_del_all(&w->wait.list), list)
                llist_add(&cl->list, &as->wait.list);

        /*
         * 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:
         */
        bch2_journal_pin_add_if_older(&c->journal, &w->journal,
                                      &as->journal, interior_update_flush);
        bch2_journal_pin_drop(&c->journal, &w->journal);

        w = btree_prev_write(b);
        bch2_journal_pin_add_if_older(&c->journal, &w->journal,
                                      &as->journal, interior_update_flush);
        bch2_journal_pin_drop(&c->journal, &w->journal);

        mutex_unlock(&c->btree_interior_update_lock);
}

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

        bch2_btree_reserve_put(as->c, as->reserve);
        as->reserve = NULL;

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

struct btree_update *
bch2_btree_update_start(struct bch_fs *c, enum btree_id id,
                        unsigned nr_nodes, unsigned flags,
                        struct closure *cl)
{
        struct btree_reserve *reserve;
        struct btree_update *as;

        if (unlikely(!percpu_ref_tryget(&c->writes)))
                return ERR_PTR(-EROFS);

        reserve = bch2_btree_reserve_get(c, nr_nodes, flags, cl);
        if (IS_ERR(reserve)) {
                percpu_ref_put(&c->writes);
                return ERR_CAST(reserve);
        }

        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;
        as->reserve     = reserve;
        INIT_LIST_HEAD(&as->write_blocked_list);

        bch2_keylist_init(&as->parent_keys, as->inline_keys);

        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;
}

/* 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->level < btree_node_root(c, b)->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);
}

static void bch2_btree_set_root_inmem(struct btree_update *as, struct btree *b)
{
        struct bch_fs *c = as->c;
        struct btree *old = btree_node_root(c, b);
        struct bch_fs_usage stats = { 0 };

        __bch2_btree_set_root_inmem(c, b);

        bch2_mark_key(c, bkey_i_to_s_c(&b->key),
                      c->opts.btree_node_size, true,
                      gc_pos_btree_root(b->btree_id),
                      &stats, 0, 0);

        if (old && !btree_node_fake(old))
                bch2_btree_node_free_index(as, NULL,
                                           bkey_i_to_s_c(&old->key),
                                           &stats);
        bch2_fs_usage_apply(c, &stats, &as->reserve->disk_res,
                            gc_pos_btree_root(b->btree_id));
}

static void bch2_btree_set_root_ondisk(struct bch_fs *c, struct btree *b, int rw)
{
        struct btree_root *r = &c->btree_roots[b->btree_id];

        mutex_lock(&c->btree_root_lock);

        BUG_ON(b != r->b);
        bkey_copy(&r->key, &b->key);
        r->level = b->level;
        r->alive = true;
        if (rw == WRITE)
                c->btree_roots_dirty = true;

        mutex_unlock(&c->btree_root_lock);
}

/**
 * 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);

        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(as, b);

        btree_update_updated_root(as);

        /*
         * 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 bch_fs *c = as->c;
        struct bch_fs_usage stats = { 0 };
        struct bkey_packed *k;
        struct bkey tmp;

        BUG_ON(insert->k.u64s > bch_btree_keys_u64s_remaining(c, b));

        if (bkey_extent_is_data(&insert->k))
                bch2_mark_key(c, bkey_i_to_s_c(insert),
                             c->opts.btree_node_size, true,
                             gc_pos_btree_node(b), &stats, 0, 0);

        while ((k = bch2_btree_node_iter_peek_all(node_iter, b)) &&
               !btree_iter_pos_cmp_packed(b, &insert->k.p, k, false))
                bch2_btree_node_iter_advance(node_iter, b);

        /*
         * If we're overwriting, look up pending delete and mark so that gc
         * marks it on the pending delete list:
         */
        if (k && !bkey_cmp_packed(b, k, &insert->k))
                bch2_btree_node_free_index(as, b,
                                           bkey_disassemble(b, k, &tmp),
                                           &stats);

        bch2_fs_usage_apply(c, &stats, &as->reserve->disk_res,
                            gc_pos_btree_node(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->level);

        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) {
                if (bkey_next(k) == 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 = bkey_next(k);
        }

        BUG_ON(!prev);

        n1->key.k.p = bkey_unpack_pos(n1, prev);
        n1->data->max_key = n1->key.k.p;
        n2->data->min_key =
                btree_type_successor(n1->btree_id, 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->level) {
                btree_node_interior_verify(n1);
                btree_node_interior_verify(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 *p;
        struct bset *i;

        BUG_ON(btree_node_type(b) != BKEY_TYPE_BTREE);

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

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

                BUG_ON(bch_keylist_u64s(keys) >
                       bch_btree_keys_u64s_remaining(as->c, b));
                BUG_ON(bkey_cmp(k->k.p, b->data->min_key) < 0);
                BUG_ON(bkey_cmp(k->k.p, b->data->max_key) > 0);

                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);
        p = i->start;
        while (p != vstruct_last(i))
                if (bkey_deleted(p)) {
                        le16_add_cpu(&i->u64s, -p->u64s);
                        set_btree_bset_end(b, b->set);
                        memmove_u64s_down(p, bkey_next(p),
                                          (u64 *) vstruct_last(i) -
                                          (u64 *) p);
                } else
                        p = bkey_next(p);

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

        btree_node_interior_verify(b);
}

static void btree_split(struct btree_update *as, struct btree *b,
                        struct btree_iter *iter, struct keylist *keys)
{
        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)->level));

        bch2_btree_interior_update_will_free_node(as, b);

        n1 = bch2_btree_node_alloc_replacement(as, b);

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

        if (vstruct_blocks(n1->data, c->block_bits) > 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->lock);
                six_unlock_write(&n1->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->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->lock);

                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);
        } 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_open_bucket_put(c, n1);
        if (n2)
                bch2_btree_open_bucket_put(c, n2);
        if (n3)
                bch2_btree_open_bucket_put(c, n3);

        /*
         * Note - at this point other linked iterators could still have @b read
         * locked; we're depending on the bch2_btree_iter_node_replace() calls
         * below removing all references to @b so we don't return with other
         * iterators pointing to a node they have locked that's been freed.
         *
         * We have to free the node first because the bch2_iter_node_replace()
         * calls will drop _our_ iterator's reference - and intent lock - to @b.
         */
        bch2_btree_node_free_inmem(c, b, iter);

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

        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);

        bch2_time_stats_update(&c->btree_split_time, 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->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))
                ;

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

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

        btree_update_updated_node(as, b);

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

        bch2_btree_iter_verify(iter, 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)
{
        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)->level));
        BUG_ON(!b->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, bch_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(b);

        bch2_foreground_maybe_merge(c, iter, b->level);
        return;
split:
        btree_split(as, b, iter, keys);
}

int bch2_btree_split_leaf(struct bch_fs *c, struct btree_iter *iter,
                          unsigned btree_reserve_flags)
{
        struct btree *b = iter->l[0].b;
        struct btree_update *as;
        struct closure cl;
        int ret = 0;

        /*
         * We already have a disk reservation and open buckets pinned; this
         * allocation must not block:
         */
        if (iter->btree_id == BTREE_ID_EXTENTS)
                btree_reserve_flags |= BTREE_INSERT_USE_RESERVE;

        closure_init_stack(&cl);

        /* Hack, because gc and splitting nodes doesn't mix yet: */
        if (!down_read_trylock(&c->gc_lock)) {
                bch2_btree_iter_unlock(iter);
                down_read(&c->gc_lock);

                if (btree_iter_linked(iter))
                        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_set_locks_want(iter, U8_MAX)) {
                ret = -EINTR;
                goto out;
        }

        as = bch2_btree_update_start(c, iter->btree_id,
                                     btree_update_reserve_required(c, b),
                                     btree_reserve_flags, &cl);
        if (IS_ERR(as)) {
                ret = PTR_ERR(as);
                if (ret == -EAGAIN) {
                        bch2_btree_iter_unlock(iter);
                        up_read(&c->gc_lock);
                        closure_sync(&cl);
                        return -EINTR;
                }
                goto out;
        }

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

        bch2_btree_iter_set_locks_want(iter, 1);
out:
        up_read(&c->gc_lock);
        closure_sync(&cl);
        return ret;
}

int __bch2_foreground_maybe_merge(struct bch_fs *c,
                                  struct btree_iter *iter,
                                  unsigned level,
                                  enum btree_node_sibling sib)
{
        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;

        closure_init_stack(&cl);
retry:
        if (!bch2_btree_node_relock(iter, level))
                return 0;

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

        parent = btree_node_parent(iter, b);
        if (!parent)
                return 0;

        if (b->sib_u64s[sib] > BTREE_FOREGROUND_MERGE_THRESHOLD(c))
                return 0;

        /* 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 out;
        }

        /* NULL means no sibling: */
        if (!m) {
                b->sib_u64s[sib] = U16_MAX;
                return 0;
        }

        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->lock);
                return 0;
        }

        /* We're changing btree topology, doesn't mix with gc: */
        if (!down_read_trylock(&c->gc_lock)) {
                six_unlock_intent(&m->lock);
                bch2_btree_iter_unlock(iter);

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

        if (!bch2_btree_iter_set_locks_want(iter, U8_MAX)) {
                ret = -EINTR;
                goto out_unlock;
        }

        as = bch2_btree_update_start(c, iter->btree_id,
                                     btree_update_reserve_required(c, b),
                                     BTREE_INSERT_NOFAIL|
                                     BTREE_INSERT_USE_RESERVE,
                                     &cl);
        if (IS_ERR(as)) {
                ret = PTR_ERR(as);
                goto out_unlock;
        }

        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->level);

        n->data->min_key        = prev->data->min_key;
        n->data->max_key        = next->data->max_key;
        n->data->format         = new_f;
        n->key.k.p              = next->key.k.p;

        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->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);

        bch2_btree_open_bucket_put(c, n);
        bch2_btree_node_free_inmem(c, b, iter);
        bch2_btree_node_free_inmem(c, m, iter);
        bch2_btree_iter_node_replace(iter, n);

        bch2_btree_iter_verify(iter, n);

        bch2_btree_update_done(as);
out_unlock:
        if (ret != -EINTR && ret != -EAGAIN)
                bch2_btree_iter_set_locks_want(iter, 1);
        six_unlock_intent(&m->lock);
        up_read(&c->gc_lock);
out:
        if (ret == -EAGAIN || ret == -EINTR) {
                bch2_btree_iter_unlock(iter);
                ret = -EINTR;
        }

        closure_sync(&cl);

        if (ret == -EINTR) {
                ret = bch2_btree_iter_traverse(iter);
                if (!ret)
                        goto retry;
        }

        return ret;
}

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(c, iter->btree_id,
                                     btree_update_reserve_required(c, b),
                                     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_build_aux_trees(n);
        six_unlock_write(&n->lock);

        trace_btree_gc_rewrite_node(c, b);

        bch2_btree_node_write(c, n, SIX_LOCK_intent);

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

        bch2_btree_open_bucket_put(c, n);

        bch2_btree_node_free_inmem(c, b, iter);

        BUG_ON(!bch2_btree_iter_node_replace(iter, n));

        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)
{
        unsigned locks_want = iter->locks_want;
        struct closure cl;
        struct btree *b;
        int ret;

        flags |= BTREE_INSERT_NOFAIL;

        closure_init_stack(&cl);

        bch2_btree_iter_set_locks_want(iter, U8_MAX);

        if (!(flags & BTREE_INSERT_GC_LOCK_HELD)) {
                if (!down_read_trylock(&c->gc_lock)) {
                        bch2_btree_iter_unlock(iter);
                        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_btree_iter_unlock(iter);
                closure_sync(&cl);
        }

        bch2_btree_iter_set_locks_want(iter, locks_want);

        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_extent *new_key)
{
        struct btree *parent;
        int ret;

        /*
         * Two corner cases that need to be thought about here:
         *
         * @b may not be reachable yet - there might be another interior update
         * operation waiting on @b to be written, and we're gonna deliver the
         * write completion to that interior update operation _before_
         * persisting the new_key update
         *
         * That ends up working without us having to do anything special here:
         * the reason is, we do kick off (and do the in memory updates) for the
         * update for @new_key before we return, creating a new interior_update
         * operation here.
         *
         * The new interior update operation here will in effect override the
         * previous one. The previous one was going to terminate - make @b
         * reachable - in one of two ways:
         * - updating the btree root pointer
         *   In that case,
         *   no, this doesn't work. argh.
         */

        if (b->will_make_reachable)
                as->must_rewrite = true;

        btree_interior_update_add_node_reference(as, b);

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

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

                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->k_i);
                        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->k_i);
                }
        } else {
                struct bch_fs_usage stats = { 0 };

                BUG_ON(btree_node_root(c, b) != b);

                bch2_btree_node_lock_write(b, iter);

                bch2_mark_key(c, bkey_i_to_s_c(&new_key->k_i),
                              c->opts.btree_node_size, true,
                              gc_pos_btree_root(b->btree_id),
                              &stats, 0, 0);
                bch2_btree_node_free_index(as, NULL,
                                           bkey_i_to_s_c(&b->key),
                                           &stats);
                bch2_fs_usage_apply(c, &stats, &as->reserve->disk_res,
                                    gc_pos_btree_root(b->btree_id));

                if (PTR_HASH(&new_key->k_i) != PTR_HASH(&b->key)) {
                        mutex_lock(&c->btree_cache.lock);
                        bch2_btree_node_hash_remove(&c->btree_cache, b);

                        bkey_copy(&b->key, &new_key->k_i);
                        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->k_i);
                }

                btree_update_updated_root(as);
                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_extent *new_key)
{
        struct btree_update *as = NULL;
        struct btree *new_hash = NULL;
        struct closure cl;
        int ret;

        closure_init_stack(&cl);

        if (!down_read_trylock(&c->gc_lock)) {
                bch2_btree_iter_unlock(iter);
                down_read(&c->gc_lock);

                if (!bch2_btree_iter_relock(iter)) {
                        ret = -EINTR;
                        goto err;
                }
        }

        /* check PTR_HASH() after @b is locked by btree_iter_traverse(): */
        if (PTR_HASH(&new_key->k_i) != PTR_HASH(&b->key)) {
                /* bch2_btree_reserve_get will unlock */
                ret = bch2_btree_cache_cannibalize_lock(c, &cl);
                if (ret) {
                        ret = -EINTR;

                        bch2_btree_iter_unlock(iter);
                        up_read(&c->gc_lock);
                        closure_sync(&cl);
                        down_read(&c->gc_lock);

                        if (!bch2_btree_iter_relock(iter))
                                goto err;
                }

                new_hash = bch2_btree_node_mem_alloc(c);
        }

        as = bch2_btree_update_start(c, iter->btree_id,
                                     btree_update_reserve_required(c, b),
                                     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)
                        goto err;

                bch2_btree_iter_unlock(iter);
                up_read(&c->gc_lock);
                closure_sync(&cl);
                down_read(&c->gc_lock);

                if (!bch2_btree_iter_relock(iter))
                        goto err;
        }

        ret = bch2_mark_bkey_replicas(c, BCH_DATA_BTREE,
                                      extent_i_to_s_c(new_key).s_c);
        if (ret)
                goto err_free_update;

        __bch2_btree_node_update_key(c, as, iter, b, new_hash, new_key);
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->lock);
                six_unlock_intent(&new_hash->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);
        bch2_btree_set_root_ondisk(c, b, READ);
}

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);
        b->level        = 0;
        b->btree_id     = id;

        bkey_extent_init(&b->key);
        b->key.k.p = POS_MAX;
        bkey_i_to_extent(&b->key)->v._data[0] = U64_MAX - id;

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

        b->data->min_key = POS_MIN;
        b->data->max_key = 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->level, b->btree_id);
        BUG_ON(ret);

        __bch2_btree_set_root_inmem(c, b);

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

ssize_t bch2_btree_updates_print(struct bch_fs *c, char *buf)
{
        char *out = buf, *end = buf + PAGE_SIZE;
        struct btree_update *as;

        mutex_lock(&c->btree_interior_update_lock);
        list_for_each_entry(as, &c->btree_interior_update_list, list)
                out += scnprintf(out, end - 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,
                                 bch2_journal_pin_seq(&c->journal, &as->journal));
        mutex_unlock(&c->btree_interior_update_lock);

        return out - buf;
}

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;
}