/*
 * Copyright (C) 2010 Kent Overstreet <kent.overstreet@gmail.com>
 *
 * Uses a block device as cache for other block devices; optimized for SSDs.
 * All allocation is done in buckets, which should match the erase block size
 * of the device.
 *
 * Buckets containing cached data are kept on a heap sorted by priority;
 * bucket priority is increased on cache hit, and periodically all the buckets
 * on the heap have their priority scaled down. This currently is just used as
 * an LRU but in the future should allow for more intelligent heuristics.
 *
 * Buckets have an 8 bit counter; freeing is accomplished by incrementing the
 * counter. Garbage collection is used to remove stale pointers.
 *
 * Indexing is done via a btree; nodes are not necessarily fully sorted, rather
 * as keys are inserted we only sort the pages that have not yet been written.
 * When garbage collection is run, we resort the entire node.
 *
 * All configuration is done via sysfs; see Documentation/bcache.txt.
 */

#include "bcache.h"
#include "btree.h"
#include "debug.h"
#include "extents.h"

#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/hash.h>
#include <linux/kthread.h>
#include <linux/prefetch.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <trace/events/bcache.h>

/*
 * Todo:
 * register_bcache: Return errors out to userspace correctly
 *
 * Writeback: don't undirty key until after a cache flush
 *
 * Create an iterator for key pointers
 *
 * On btree write error, mark bucket such that it won't be freed from the cache
 *
 * Journalling:
 *   Check for bad keys in replay
 *   Propagate barriers
 *   Refcount journal entries in journal_replay
 *
 * Garbage collection:
 *   Finish incremental gc
 *   Gc should free old UUIDs, data for invalid UUIDs
 *
 * Provide a way to list backing device UUIDs we have data cached for, and
 * probably how long it's been since we've seen them, and a way to invalidate
 * dirty data for devices that will never be attached again
 *
 * Keep 1 min/5 min/15 min statistics of how busy a block device has been, so
 * that based on that and how much dirty data we have we can keep writeback
 * from being starved
 *
 * Add a tracepoint or somesuch to watch for writeback starvation
 *
 * When btree depth > 1 and splitting an interior node, we have to make sure
 * alloc_bucket() cannot fail. This should be true but is not completely
 * obvious.
 *
 * Plugging?
 *
 * If data write is less than hard sector size of ssd, round up offset in open
 * bucket to the next whole sector
 *
 * Superblock needs to be fleshed out for multiple cache devices
 *
 * Add a sysfs tunable for the number of writeback IOs in flight
 *
 * Add a sysfs tunable for the number of open data buckets
 *
 * IO tracking: Can we track when one process is doing io on behalf of another?
 * IO tracking: Don't use just an average, weigh more recent stuff higher
 *
 * Test module load/unload
 */

#define MAX_NEED_GC             64
#define MAX_SAVE_PRIO           72

#define PTR_DIRTY_BIT           (((uint64_t) 1 << 36))

#define PTR_HASH(c, k)                                                  \
        (((k)->ptr[0] >> c->bucket_bits) | PTR_GEN(k, 0))

#define insert_lock(s, b)       ((b)->level <= (s)->lock)

/*
 * These macros are for recursing down the btree - they handle the details of
 * locking and looking up nodes in the cache for you. They're best treated as
 * mere syntax when reading code that uses them.
 *
 * op->lock determines whether we take a read or a write lock at a given depth.
 * If you've got a read lock and find that you need a write lock (i.e. you're
 * going to have to split), set op->lock and return -EINTR; btree_root() will
 * call you again and you'll have the correct lock.
 */

/**
 * btree - recurse down the btree on a specified key
 * @fn:         function to call, which will be passed the child node
 * @key:        key to recurse on
 * @b:          parent btree node
 * @op:         pointer to struct btree_op
 */
#define btree(fn, key, b, op, ...)                                      \
({                                                                      \
        int _r, l = (b)->level - 1;                                     \
        bool _w = l <= (op)->lock;                                      \
        struct btree *_child = bch_btree_node_get((b)->c, op, key, l,   \
                                                  _w, b);               \
        if (!IS_ERR(_child)) {                                          \
                _r = bch_btree_ ## fn(_child, op, ##__VA_ARGS__);       \
                rw_unlock(_w, _child);                                  \
        } else                                                          \
                _r = PTR_ERR(_child);                                   \
        _r;                                                             \
})

/**
 * btree_root - call a function on the root of the btree
 * @fn:         function to call, which will be passed the child node
 * @c:          cache set
 * @op:         pointer to struct btree_op
 */
#define btree_root(fn, c, op, ...)                                      \
({                                                                      \
        int _r = -EINTR;                                                \
        do {                                                            \
                struct btree *_b = (c)->root;                           \
                bool _w = insert_lock(op, _b);                          \
                rw_lock(_w, _b, _b->level);                             \
                if (_b == (c)->root &&                                  \
                    _w == insert_lock(op, _b)) {                        \
                        _r = bch_btree_ ## fn(_b, op, ##__VA_ARGS__);   \
                }                                                       \
                rw_unlock(_w, _b);                                      \
                bch_cannibalize_unlock(c);                              \
                if (_r == -EINTR)                                       \
                        schedule();                                     \
        } while (_r == -EINTR);                                         \
                                                                        \
        finish_wait(&(c)->btree_cache_wait, &(op)->wait);               \
        _r;                                                             \
})

static inline struct bset *write_block(struct btree *b)
{
        return ((void *) btree_bset_first(b)) + b->written * block_bytes(b->c);
}

static void bch_btree_init_next(struct btree *b)
{
        /* If not a leaf node, always sort */
        if (b->level && b->keys.nsets)
                bch_btree_sort(&b->keys, &b->c->sort);
        else
                bch_btree_sort_lazy(&b->keys, &b->c->sort);

        if (b->written < btree_blocks(b))
                bch_bset_init_next(&b->keys, write_block(b),
                                   bset_magic(&b->c->sb));

}

/* Btree key manipulation */

void bkey_put(struct cache_set *c, struct bkey *k)
{
        unsigned i;

        for (i = 0; i < KEY_PTRS(k); i++)
                if (ptr_available(c, k, i))
                        atomic_dec_bug(&PTR_BUCKET(c, k, i)->pin);
}

/* Btree IO */

static uint64_t btree_csum_set(struct btree *b, struct bset *i)
{
        uint64_t crc = b->key.ptr[0];
        void *data = (void *) i + 8, *end = bset_bkey_last(i);

        crc = bch_crc64_update(crc, data, end - data);
        return crc ^ 0xffffffffffffffffULL;
}

void bch_btree_node_read_done(struct btree *b)
{
        const char *err = "bad btree header";
        struct bset *i = btree_bset_first(b);
        struct btree_iter *iter;

        iter = mempool_alloc(b->c->fill_iter, GFP_NOIO);
        iter->size = b->c->sb.bucket_size / b->c->sb.block_size;
        iter->used = 0;

#ifdef CONFIG_BCACHE_DEBUG
        iter->b = &b->keys;
#endif

        if (!i->seq)
                goto err;

        for (;
             b->written < btree_blocks(b) && i->seq == b->keys.set[0].data->seq;
             i = write_block(b)) {
                err = "unsupported bset version";
                if (i->version > BCACHE_BSET_VERSION)
                        goto err;

                err = "bad btree header";
                if (b->written + set_blocks(i, block_bytes(b->c)) >
                    btree_blocks(b))
                        goto err;

                err = "bad magic";
                if (i->magic != bset_magic(&b->c->sb))
                        goto err;

                err = "bad checksum";
                switch (i->version) {
                case 0:
                        if (i->csum != csum_set(i))
                                goto err;
                        break;
                case BCACHE_BSET_VERSION:
                        if (i->csum != btree_csum_set(b, i))
                                goto err;
                        break;
                }

                err = "empty set";
                if (i != b->keys.set[0].data && !i->keys)
                        goto err;

                bch_btree_iter_push(iter, i->start, bset_bkey_last(i));

                b->written += set_blocks(i, block_bytes(b->c));
        }

        err = "corrupted btree";
        for (i = write_block(b);
             bset_sector_offset(&b->keys, i) < KEY_SIZE(&b->key);
             i = ((void *) i) + block_bytes(b->c))
                if (i->seq == b->keys.set[0].data->seq)
                        goto err;

        bch_btree_sort_and_fix_extents(&b->keys, iter, &b->c->sort);

        i = b->keys.set[0].data;
        err = "short btree key";
        if (b->keys.set[0].size &&
            bkey_cmp(&b->key, &b->keys.set[0].end) < 0)
                goto err;

        if (b->written < btree_blocks(b))
                bch_bset_init_next(&b->keys, write_block(b),
                                   bset_magic(&b->c->sb));
out:
        mempool_free(iter, b->c->fill_iter);
        return;
err:
        set_btree_node_io_error(b);
        bch_cache_set_error(b->c, "%s at bucket %zu, block %u, %u keys",
                            err, PTR_BUCKET_NR(b->c, &b->key, 0),
                            bset_block_offset(b, i), i->keys);
        goto out;
}

static void btree_node_read_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;
        closure_put(cl);
}

static void bch_btree_node_read(struct btree *b)
{
        uint64_t start_time = local_clock();
        struct closure cl;
        struct bio *bio;

        trace_bcache_btree_read(b);

        closure_init_stack(&cl);

        bio = bch_bbio_alloc(b->c);
        bio->bi_iter.bi_size = KEY_SIZE(&b->key) << 9;
        bio->bi_end_io  = btree_node_read_endio;
        bio->bi_private = &cl;
        bio_set_op_attrs(bio, REQ_OP_READ, REQ_META|READ_SYNC);

        bch_bio_map(bio, b->keys.set[0].data);

        bch_submit_bbio(bio, b->c, &b->key, 0);
        closure_sync(&cl);

        if (bio->bi_error)
                set_btree_node_io_error(b);

        bch_bbio_free(bio, b->c);

        if (btree_node_io_error(b))
                goto err;

        bch_btree_node_read_done(b);
        bch_time_stats_update(&b->c->btree_read_time, start_time);

        return;
err:
        bch_cache_set_error(b->c, "io error reading bucket %zu",
                            PTR_BUCKET_NR(b->c, &b->key, 0));
}

static void btree_complete_write(struct btree *b, struct btree_write *w)
{
        if (w->prio_blocked &&
            !atomic_sub_return(w->prio_blocked, &b->c->prio_blocked))
                wake_up_allocators(b->c);

        if (w->journal) {
                atomic_dec_bug(w->journal);
                __closure_wake_up(&b->c->journal.wait);
        }

        w->prio_blocked = 0;
        w->journal      = NULL;
}

static void btree_node_write_unlock(struct closure *cl)
{
        struct btree *b = container_of(cl, struct btree, io);

        up(&b->io_mutex);
}

static void __btree_node_write_done(struct closure *cl)
{
        struct btree *b = container_of(cl, struct btree, io);
        struct btree_write *w = btree_prev_write(b);

        bch_bbio_free(b->bio, b->c);
        b->bio = NULL;
        btree_complete_write(b, w);

        if (btree_node_dirty(b))
                schedule_delayed_work(&b->work, 30 * HZ);

        closure_return_with_destructor(cl, btree_node_write_unlock);
}

static void btree_node_write_done(struct closure *cl)
{
        struct btree *b = container_of(cl, struct btree, io);
        struct bio_vec *bv;
        int n;

        bio_for_each_segment_all(bv, b->bio, n)
                __free_page(bv->bv_page);

        __btree_node_write_done(cl);
}

static void btree_node_write_endio(struct bio *bio)
{
        struct closure *cl = bio->bi_private;
        struct btree *b = container_of(cl, struct btree, io);

        if (bio->bi_error)
                set_btree_node_io_error(b);

        bch_bbio_count_io_errors(b->c, bio, bio->bi_error, "writing btree");
        closure_put(cl);
}

static void do_btree_node_write(struct btree *b)
{
        struct closure *cl = &b->io;
        struct bset *i = btree_bset_last(b);
        BKEY_PADDED(key) k;

        i->version      = BCACHE_BSET_VERSION;
        i->csum         = btree_csum_set(b, i);

        BUG_ON(b->bio);
        b->bio = bch_bbio_alloc(b->c);

        b->bio->bi_end_io       = btree_node_write_endio;
        b->bio->bi_private      = cl;
        b->bio->bi_iter.bi_size = roundup(set_bytes(i), block_bytes(b->c));
        bio_set_op_attrs(b->bio, REQ_OP_WRITE, REQ_META|WRITE_SYNC|REQ_FUA);
        bch_bio_map(b->bio, i);

        /*
         * If we're appending to a leaf node, we don't technically need FUA -
         * this write just needs to be persisted before the next journal write,
         * which will be marked FLUSH|FUA.
         *
         * Similarly if we're writing a new btree root - the pointer is going to
         * be in the next journal entry.
         *
         * But if we're writing a new btree node (that isn't a root) or
         * appending to a non leaf btree node, we need either FUA or a flush
         * when we write the parent with the new pointer. FUA is cheaper than a
         * flush, and writes appending to leaf nodes aren't blocking anything so
         * just make all btree node writes FUA to keep things sane.
         */

        bkey_copy(&k.key, &b->key);
        SET_PTR_OFFSET(&k.key, 0, PTR_OFFSET(&k.key, 0) +
                       bset_sector_offset(&b->keys, i));

        if (!bio_alloc_pages(b->bio, __GFP_NOWARN|GFP_NOWAIT)) {
                int j;
                struct bio_vec *bv;
                void *base = (void *) ((unsigned long) i & ~(PAGE_SIZE - 1));

                bio_for_each_segment_all(bv, b->bio, j)
                        memcpy(page_address(bv->bv_page),
                               base + j * PAGE_SIZE, PAGE_SIZE);

                bch_submit_bbio(b->bio, b->c, &k.key, 0);

                continue_at(cl, btree_node_write_done, NULL);
        } else {
                b->bio->bi_vcnt = 0;
                bch_bio_map(b->bio, i);

                bch_submit_bbio(b->bio, b->c, &k.key, 0);

                closure_sync(cl);
                continue_at_nobarrier(cl, __btree_node_write_done, NULL);
        }
}

void __bch_btree_node_write(struct btree *b, struct closure *parent)
{
        struct bset *i = btree_bset_last(b);

        lockdep_assert_held(&b->write_lock);

        trace_bcache_btree_write(b);

        BUG_ON(current->bio_list);
        BUG_ON(b->written >= btree_blocks(b));
        BUG_ON(b->written && !i->keys);
        BUG_ON(btree_bset_first(b)->seq != i->seq);
        bch_check_keys(&b->keys, "writing");

        cancel_delayed_work(&b->work);

        /* If caller isn't waiting for write, parent refcount is cache set */
        down(&b->io_mutex);
        closure_init(&b->io, parent ?: &b->c->cl);

        clear_bit(BTREE_NODE_dirty,      &b->flags);
        change_bit(BTREE_NODE_write_idx, &b->flags);

        do_btree_node_write(b);

        atomic_long_add(set_blocks(i, block_bytes(b->c)) * b->c->sb.block_size,
                        &PTR_CACHE(b->c, &b->key, 0)->btree_sectors_written);

        b->written += set_blocks(i, block_bytes(b->c));
}

void bch_btree_node_write(struct btree *b, struct closure *parent)
{
        unsigned nsets = b->keys.nsets;

        lockdep_assert_held(&b->lock);

        __bch_btree_node_write(b, parent);

        /*
         * do verify if there was more than one set initially (i.e. we did a
         * sort) and we sorted down to a single set:
         */
        if (nsets && !b->keys.nsets)
                bch_btree_verify(b);

        bch_btree_init_next(b);
}

static void bch_btree_node_write_sync(struct btree *b)
{
        struct closure cl;

        closure_init_stack(&cl);

        mutex_lock(&b->write_lock);
        bch_btree_node_write(b, &cl);
        mutex_unlock(&b->write_lock);

        closure_sync(&cl);
}

static void btree_node_write_work(struct work_struct *w)
{
        struct btree *b = container_of(to_delayed_work(w), struct btree, work);

        mutex_lock(&b->write_lock);
        if (btree_node_dirty(b))
                __bch_btree_node_write(b, NULL);
        mutex_unlock(&b->write_lock);
}

static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref)
{
        struct bset *i = btree_bset_last(b);
        struct btree_write *w = btree_current_write(b);

        lockdep_assert_held(&b->write_lock);

        BUG_ON(!b->written);
        BUG_ON(!i->keys);

        if (!btree_node_dirty(b))
                schedule_delayed_work(&b->work, 30 * HZ);

        set_btree_node_dirty(b);

        if (journal_ref) {
                if (w->journal &&
                    journal_pin_cmp(b->c, w->journal, journal_ref)) {
                        atomic_dec_bug(w->journal);
                        w->journal = NULL;
                }

                if (!w->journal) {
                        w->journal = journal_ref;
                        atomic_inc(w->journal);
                }
        }

        /* Force write if set is too big */
        if (set_bytes(i) > PAGE_SIZE - 48 &&
            !current->bio_list)
                bch_btree_node_write(b, NULL);
}

/*
 * Btree in memory cache - allocation/freeing
 * mca -> memory cache
 */

#define mca_reserve(c)  (((c->root && c->root->level)           \
                          ? c->root->level : 1) * 8 + 16)
#define mca_can_free(c)                                         \
        max_t(int, 0, c->btree_cache_used - mca_reserve(c))

static void mca_data_free(struct btree *b)
{
        BUG_ON(b->io_mutex.count != 1);

        bch_btree_keys_free(&b->keys);

        b->c->btree_cache_used--;
        list_move(&b->list, &b->c->btree_cache_freed);
}

static void mca_bucket_free(struct btree *b)
{
        BUG_ON(btree_node_dirty(b));

        b->key.ptr[0] = 0;
        hlist_del_init_rcu(&b->hash);
        list_move(&b->list, &b->c->btree_cache_freeable);
}

static unsigned btree_order(struct bkey *k)
{
        return ilog2(KEY_SIZE(k) / PAGE_SECTORS ?: 1);
}

static void mca_data_alloc(struct btree *b, struct bkey *k, gfp_t gfp)
{
        if (!bch_btree_keys_alloc(&b->keys,
                                  max_t(unsigned,
                                        ilog2(b->c->btree_pages),
                                        btree_order(k)),
                                  gfp)) {
                b->c->btree_cache_used++;
                list_move(&b->list, &b->c->btree_cache);
        } else {
                list_move(&b->list, &b->c->btree_cache_freed);
        }
}

static struct btree *mca_bucket_alloc(struct cache_set *c,
                                      struct bkey *k, gfp_t gfp)
{
        struct btree *b = kzalloc(sizeof(struct btree), gfp);
        if (!b)
                return NULL;

        init_rwsem(&b->lock);
        lockdep_set_novalidate_class(&b->lock);
        mutex_init(&b->write_lock);
        lockdep_set_novalidate_class(&b->write_lock);
        INIT_LIST_HEAD(&b->list);
        INIT_DELAYED_WORK(&b->work, btree_node_write_work);
        b->c = c;
        sema_init(&b->io_mutex, 1);

        mca_data_alloc(b, k, gfp);
        return b;
}

static int mca_reap(struct btree *b, unsigned min_order, bool flush)
{
        struct closure cl;

        closure_init_stack(&cl);
        lockdep_assert_held(&b->c->bucket_lock);

        if (!down_write_trylock(&b->lock))
                return -ENOMEM;

        BUG_ON(btree_node_dirty(b) && !b->keys.set[0].data);

        if (b->keys.page_order < min_order)
                goto out_unlock;

        if (!flush) {
                if (btree_node_dirty(b))
                        goto out_unlock;

                if (down_trylock(&b->io_mutex))
                        goto out_unlock;
                up(&b->io_mutex);
        }

        mutex_lock(&b->write_lock);
        if (btree_node_dirty(b))
                __bch_btree_node_write(b, &cl);
        mutex_unlock(&b->write_lock);

        closure_sync(&cl);

        /* wait for any in flight btree write */
        down(&b->io_mutex);
        up(&b->io_mutex);

        return 0;
out_unlock:
        rw_unlock(true, b);
        return -ENOMEM;
}

static unsigned long bch_mca_scan(struct shrinker *shrink,
                                  struct shrink_control *sc)
{
        struct cache_set *c = container_of(shrink, struct cache_set, shrink);
        struct btree *b, *t;
        unsigned long i, nr = sc->nr_to_scan;
        unsigned long freed = 0;

        if (c->shrinker_disabled)
                return SHRINK_STOP;

        if (c->btree_cache_alloc_lock)
                return SHRINK_STOP;

        /* Return -1 if we can't do anything right now */
        if (sc->gfp_mask & __GFP_IO)
                mutex_lock(&c->bucket_lock);
        else if (!mutex_trylock(&c->bucket_lock))
                return -1;

        /*
         * It's _really_ critical that we don't free too many btree nodes - we
         * have to always leave ourselves a reserve. The reserve is how we
         * guarantee that allocating memory for a new btree node can always
         * succeed, so that inserting keys into the btree can always succeed and
         * IO can always make forward progress:
         */
        nr /= c->btree_pages;
        nr = min_t(unsigned long, nr, mca_can_free(c));

        i = 0;
        list_for_each_entry_safe(b, t, &c->btree_cache_freeable, list) {
                if (freed >= nr)
                        break;

                if (++i > 3 &&
                    !mca_reap(b, 0, false)) {
                        mca_data_free(b);
                        rw_unlock(true, b);
                        freed++;
                }
        }

        for (i = 0; (nr--) && i < c->btree_cache_used; i++) {
                if (list_empty(&c->btree_cache))
                        goto out;

                b = list_first_entry(&c->btree_cache, struct btree, list);
                list_rotate_left(&c->btree_cache);

                if (!b->accessed &&
                    !mca_reap(b, 0, false)) {
                        mca_bucket_free(b);
                        mca_data_free(b);
                        rw_unlock(true, b);
                        freed++;
                } else
                        b->accessed = 0;
        }
out:
        mutex_unlock(&c->bucket_lock);
        return freed;
}

static unsigned long bch_mca_count(struct shrinker *shrink,
                                   struct shrink_control *sc)
{
        struct cache_set *c = container_of(shrink, struct cache_set, shrink);

        if (c->shrinker_disabled)
                return 0;

        if (c->btree_cache_alloc_lock)
                return 0;

        return mca_can_free(c) * c->btree_pages;
}

void bch_btree_cache_free(struct cache_set *c)
{
        struct btree *b;
        struct closure cl;
        closure_init_stack(&cl);

        if (c->shrink.list.next)
                unregister_shrinker(&c->shrink);

        mutex_lock(&c->bucket_lock);

#ifdef CONFIG_BCACHE_DEBUG
        if (c->verify_data)
                list_move(&c->verify_data->list, &c->btree_cache);

        free_pages((unsigned long) c->verify_ondisk, ilog2(bucket_pages(c)));
#endif

        list_splice(&c->btree_cache_freeable,
                    &c->btree_cache);

        while (!list_empty(&c->btree_cache)) {
                b = list_first_entry(&c->btree_cache, struct btree, list);

                if (btree_node_dirty(b))
                        btree_complete_write(b, btree_current_write(b));
                clear_bit(BTREE_NODE_dirty, &b->flags);

                mca_data_free(b);
        }

        while (!list_empty(&c->btree_cache_freed)) {
                b = list_first_entry(&c->btree_cache_freed,
                                     struct btree, list);
                list_del(&b->list);
                cancel_delayed_work_sync(&b->work);
                kfree(b);
        }

        mutex_unlock(&c->bucket_lock);
}

int bch_btree_cache_alloc(struct cache_set *c)
{
        unsigned i;

        for (i = 0; i < mca_reserve(c); i++)
                if (!mca_bucket_alloc(c, &ZERO_KEY, GFP_KERNEL))
                        return -ENOMEM;

        list_splice_init(&c->btree_cache,
                         &c->btree_cache_freeable);

#ifdef CONFIG_BCACHE_DEBUG
        mutex_init(&c->verify_lock);

        c->verify_ondisk = (void *)
                __get_free_pages(GFP_KERNEL, ilog2(bucket_pages(c)));

        c->verify_data = mca_bucket_alloc(c, &ZERO_KEY, GFP_KERNEL);

        if (c->verify_data &&
            c->verify_data->keys.set->data)
                list_del_init(&c->verify_data->list);
        else
                c->verify_data = NULL;
#endif

        c->shrink.count_objects = bch_mca_count;
        c->shrink.scan_objects = bch_mca_scan;
        c->shrink.seeks = 4;
        c->shrink.batch = c->btree_pages * 2;
        register_shrinker(&c->shrink);

        return 0;
}

/* Btree in memory cache - hash table */

static struct hlist_head *mca_hash(struct cache_set *c, struct bkey *k)
{
        return &c->bucket_hash[hash_32(PTR_HASH(c, k), BUCKET_HASH_BITS)];
}

static struct btree *mca_find(struct cache_set *c, struct bkey *k)
{
        struct btree *b;

        rcu_read_lock();
        hlist_for_each_entry_rcu(b, mca_hash(c, k), hash)
                if (PTR_HASH(c, &b->key) == PTR_HASH(c, k))
                        goto out;
        b = NULL;
out:
        rcu_read_unlock();
        return b;
}

static int mca_cannibalize_lock(struct cache_set *c, struct btree_op *op)
{
        struct task_struct *old;

        old = cmpxchg(&c->btree_cache_alloc_lock, NULL, current);
        if (old && old != current) {
                if (op)
                        prepare_to_wait(&c->btree_cache_wait, &op->wait,
                                        TASK_UNINTERRUPTIBLE);
                return -EINTR;
        }

        return 0;
}

static struct btree *mca_cannibalize(struct cache_set *c, struct btree_op *op,
                                     struct bkey *k)
{
        struct btree *b;

        trace_bcache_btree_cache_cannibalize(c);

        if (mca_cannibalize_lock(c, op))
                return ERR_PTR(-EINTR);

        list_for_each_entry_reverse(b, &c->btree_cache, list)
                if (!mca_reap(b, btree_order(k), false))
                        return b;

        list_for_each_entry_reverse(b, &c->btree_cache, list)
                if (!mca_reap(b, btree_order(k), true))
                        return b;

        WARN(1, "btree cache cannibalize failed\n");
        return ERR_PTR(-ENOMEM);
}

/*
 * We can only have one thread cannibalizing other cached btree nodes at a time,
 * or we'll deadlock. We use an open coded mutex to ensure that, which a
 * cannibalize_bucket() will take. This means every time we unlock the root of
 * the btree, we need to release this lock if we have it held.
 */
static void bch_cannibalize_unlock(struct cache_set *c)
{
        if (c->btree_cache_alloc_lock == current) {
                c->btree_cache_alloc_lock = NULL;
                wake_up(&c->btree_cache_wait);
        }
}

static struct btree *mca_alloc(struct cache_set *c, struct btree_op *op,
                               struct bkey *k, int level)
{
        struct btree *b;

        BUG_ON(current->bio_list);

        lockdep_assert_held(&c->bucket_lock);

        if (mca_find(c, k))
                return NULL;

        /* btree_free() doesn't free memory; it sticks the node on the end of
         * the list. Check if there's any freed nodes there:
         */
        list_for_each_entry(b, &c->btree_cache_freeable, list)
                if (!mca_reap(b, btree_order(k), false))
                        goto out;

        /* We never free struct btree itself, just the memory that holds the on
         * disk node. Check the freed list before allocating a new one:
         */
        list_for_each_entry(b, &c->btree_cache_freed, list)
                if (!mca_reap(b, 0, false)) {
                        mca_data_alloc(b, k, __GFP_NOWARN|GFP_NOIO);
                        if (!b->keys.set[0].data)
                                goto err;
                        else
                                goto out;
                }

        b = mca_bucket_alloc(c, k, __GFP_NOWARN|GFP_NOIO);
        if (!b)
                goto err;

        BUG_ON(!down_write_trylock(&b->lock));
        if (!b->keys.set->data)
                goto err;
out:
        BUG_ON(b->io_mutex.count != 1);

        bkey_copy(&b->key, k);
        list_move(&b->list, &c->btree_cache);
        hlist_del_init_rcu(&b->hash);
        hlist_add_head_rcu(&b->hash, mca_hash(c, k));

        lock_set_subclass(&b->lock.dep_map, level + 1, _THIS_IP_);
        b->parent       = (void *) ~0UL;
        b->flags        = 0;
        b->written      = 0;
        b->level        = level;

        if (!b->level)
                bch_btree_keys_init(&b->keys, &bch_extent_keys_ops,
                                    &b->c->expensive_debug_checks);
        else
                bch_btree_keys_init(&b->keys, &bch_btree_keys_ops,
                                    &b->c->expensive_debug_checks);

        return b;
err:
        if (b)
                rw_unlock(true, b);

        b = mca_cannibalize(c, op, k);
        if (!IS_ERR(b))
                goto out;

        return b;
}

/**
 * bch_btree_node_get - find a btree node in the cache and lock it, reading it
 * in from disk if necessary.
 *
 * If IO is necessary and running under generic_make_request, returns -EAGAIN.
 *
 * The btree node will have either a read or a write lock held, depending on
 * level and op->lock.
 */
struct btree *bch_btree_node_get(struct cache_set *c, struct btree_op *op,
                                 struct bkey *k, int level, bool write,
                                 struct btree *parent)
{
        int i = 0;
        struct btree *b;

        BUG_ON(level < 0);
retry:
        b = mca_find(c, k);

        if (!b) {
                if (current->bio_list)
                        return ERR_PTR(-EAGAIN);

                mutex_lock(&c->bucket_lock);
                b = mca_alloc(c, op, k, level);
                mutex_unlock(&c->bucket_lock);

                if (!b)
                        goto retry;
                if (IS_ERR(b))
                        return b;

                bch_btree_node_read(b);

                if (!write)
                        downgrade_write(&b->lock);
        } else {
                rw_lock(write, b, level);
                if (PTR_HASH(c, &b->key) != PTR_HASH(c, k)) {
                        rw_unlock(write, b);
                        goto retry;
                }

                BUG_ON(b->level != level);
        }

        b->parent = parent;
        b->accessed = 1;

        for (; i <= b->keys.nsets && b->keys.set[i].size; i++) {
                prefetch(b->keys.set[i].tree);
                prefetch(b->keys.set[i].data);
        }

        for (; i <= b->keys.nsets; i++)
                prefetch(b->keys.set[i].data);

        if (btree_node_io_error(b)) {
                rw_unlock(write, b);
                return ERR_PTR(-EIO);
        }

        BUG_ON(!b->written);

        return b;
}

static void btree_node_prefetch(struct btree *parent, struct bkey *k)
{
        struct btree *b;

        mutex_lock(&parent->c->bucket_lock);
        b = mca_alloc(parent->c, NULL, k, parent->level - 1);
        mutex_unlock(&parent->c->bucket_lock);

        if (!IS_ERR_OR_NULL(b)) {
                b->parent = parent;
                bch_btree_node_read(b);
                rw_unlock(true, b);
        }
}

/* Btree alloc */

static void btree_node_free(struct btree *b)
{
        trace_bcache_btree_node_free(b);

        BUG_ON(b == b->c->root);

        mutex_lock(&b->write_lock);

        if (btree_node_dirty(b))
                btree_complete_write(b, btree_current_write(b));
        clear_bit(BTREE_NODE_dirty, &b->flags);

        mutex_unlock(&b->write_lock);

        cancel_delayed_work(&b->work);

        mutex_lock(&b->c->bucket_lock);
        bch_bucket_free(b->c, &b->key);
        mca_bucket_free(b);
        mutex_unlock(&b->c->bucket_lock);
}

struct btree *__bch_btree_node_alloc(struct cache_set *c, struct btree_op *op,
                                     int level, bool wait,
                                     struct btree *parent)
{
        BKEY_PADDED(key) k;
        struct btree *b = ERR_PTR(-EAGAIN);

        mutex_lock(&c->bucket_lock);
retry:
        if (__bch_bucket_alloc_set(c, RESERVE_BTREE, &k.key, 1, wait))
                goto err;

        bkey_put(c, &k.key);
        SET_KEY_SIZE(&k.key, c->btree_pages * PAGE_SECTORS);

        b = mca_alloc(c, op, &k.key, level);
        if (IS_ERR(b))
                goto err_free;

        if (!b) {
                cache_bug(c,
                        "Tried to allocate bucket that was in btree cache");
                goto retry;
        }

        b->accessed = 1;
        b->parent = parent;
        bch_bset_init_next(&b->keys, b->keys.set->data, bset_magic(&b->c->sb));

        mutex_unlock(&c->bucket_lock);

        trace_bcache_btree_node_alloc(b);
        return b;
err_free:
        bch_bucket_free(c, &k.key);
err:
        mutex_unlock(&c->bucket_lock);

        trace_bcache_btree_node_alloc_fail(c);
        return b;
}

static struct btree *bch_btree_node_alloc(struct cache_set *c,
                                          struct btree_op *op, int level,
                                          struct btree *parent)
{
        return __bch_btree_node_alloc(c, op, level, op != NULL, parent);
}

static struct btree *btree_node_alloc_replacement(struct btree *b,
                                                  struct btree_op *op)
{
        struct btree *n = bch_btree_node_alloc(b->c, op, b->level, b->parent);
        if (!IS_ERR_OR_NULL(n)) {
                mutex_lock(&n->write_lock);
                bch_btree_sort_into(&b->keys, &n->keys, &b->c->sort);
                bkey_copy_key(&n->key, &b->key);
                mutex_unlock(&n->write_lock);
        }

        return n;
}

static void make_btree_freeing_key(struct btree *b, struct bkey *k)
{
        unsigned i;

        mutex_lock(&b->c->bucket_lock);

        atomic_inc(&b->c->prio_blocked);

        bkey_copy(k, &b->key);
        bkey_copy_key(k, &ZERO_KEY);

        for (i = 0; i < KEY_PTRS(k); i++)
                SET_PTR_GEN(k, i,
                            bch_inc_gen(PTR_CACHE(b->c, &b->key, i),
                                        PTR_BUCKET(b->c, &b->key, i)));

        mutex_unlock(&b->c->bucket_lock);
}

static int btree_check_reserve(struct btree *b, struct btree_op *op)
{
        struct cache_set *c = b->c;
        struct cache *ca;
        unsigned i, reserve = (c->root->level - b->level) * 2 + 1;

        mutex_lock(&c->bucket_lock);

        for_each_cache(ca, c, i)
                if (fifo_used(&ca->free[RESERVE_BTREE]) < reserve) {
                        if (op)
                                prepare_to_wait(&c->btree_cache_wait, &op->wait,
                                                TASK_UNINTERRUPTIBLE);
                        mutex_unlock(&c->bucket_lock);
                        return -EINTR;
                }

        mutex_unlock(&c->bucket_lock);

        return mca_cannibalize_lock(b->c, op);
}

/* Garbage collection */

static uint8_t __bch_btree_mark_key(struct cache_set *c, int level,
                                    struct bkey *k)
{
        uint8_t stale = 0;
        unsigned i;
        struct bucket *g;

        /*
         * ptr_invalid() can't return true for the keys that mark btree nodes as
         * freed, but since ptr_bad() returns true we'll never actually use them
         * for anything and thus we don't want mark their pointers here
         */
        if (!bkey_cmp(k, &ZERO_KEY))
                return stale;

        for (i = 0; i < KEY_PTRS(k); i++) {
                if (!ptr_available(c, k, i))
                        continue;

                g = PTR_BUCKET(c, k, i);

                if (gen_after(g->last_gc, PTR_GEN(k, i)))
                        g->last_gc = PTR_GEN(k, i);

                if (ptr_stale(c, k, i)) {
                        stale = max(stale, ptr_stale(c, k, i));
                        continue;
                }

                cache_bug_on(GC_MARK(g) &&
                             (GC_MARK(g) == GC_MARK_METADATA) != (level != 0),
                             c, "inconsistent ptrs: mark = %llu, level = %i",
                             GC_MARK(g), level);

                if (level)
                        SET_GC_MARK(g, GC_MARK_METADATA);
                else if (KEY_DIRTY(k))
                        SET_GC_MARK(g, GC_MARK_DIRTY);
                else if (!GC_MARK(g))
                        SET_GC_MARK(g, GC_MARK_RECLAIMABLE);

                /* guard against overflow */
                SET_GC_SECTORS_USED(g, min_t(unsigned,
                                             GC_SECTORS_USED(g) + KEY_SIZE(k),
                                             MAX_GC_SECTORS_USED));

                BUG_ON(!GC_SECTORS_USED(g));
        }

        return stale;
}

#define btree_mark_key(b, k)    __bch_btree_mark_key(b->c, b->level, k)

void bch_initial_mark_key(struct cache_set *c, int level, struct bkey *k)
{
        unsigned i;

        for (i = 0; i < KEY_PTRS(k); i++)
                if (ptr_available(c, k, i) &&
                    !ptr_stale(c, k, i)) {
                        struct bucket *b = PTR_BUCKET(c, k, i);

                        b->gen = PTR_GEN(k, i);

                        if (level && bkey_cmp(k, &ZERO_KEY))
                                b->prio = BTREE_PRIO;
                        else if (!level && b->prio == BTREE_PRIO)
                                b->prio = INITIAL_PRIO;
                }

        __bch_btree_mark_key(c, level, k);
}

static bool btree_gc_mark_node(struct btree *b, struct gc_stat *gc)
{
        uint8_t stale = 0;
        unsigned keys = 0, good_keys = 0;
        struct bkey *k;
        struct btree_iter iter;
        struct bset_tree *t;

        gc->nodes++;

        for_each_key_filter(&b->keys, k, &iter, bch_ptr_invalid) {
                stale = max(stale, btree_mark_key(b, k));
                keys++;

                if (bch_ptr_bad(&b->keys, k))
                        continue;

                gc->key_bytes += bkey_u64s(k);
                gc->nkeys++;
                good_keys++;

                gc->data += KEY_SIZE(k);
        }

        for (t = b->keys.set; t <= &b->keys.set[b->keys.nsets]; t++)
                btree_bug_on(t->size &&
                             bset_written(&b->keys, t) &&
                             bkey_cmp(&b->key, &t->end) < 0,
                             b, "found short btree key in gc");

        if (b->c->gc_always_rewrite)
                return true;

        if (stale > 10)
                return true;

        if ((keys - good_keys) * 2 > keys)
                return true;

        return false;
}

#define GC_MERGE_NODES  4U

struct gc_merge_info {
        struct btree    *b;
        unsigned        keys;
};

static int bch_btree_insert_node(struct btree *, struct btree_op *,
                                 struct keylist *, atomic_t *, struct bkey *);

static int btree_gc_coalesce(struct btree *b, struct btree_op *op,
                             struct gc_stat *gc, struct gc_merge_info *r)
{
        unsigned i, nodes = 0, keys = 0, blocks;
        struct btree *new_nodes[GC_MERGE_NODES];
        struct keylist keylist;
        struct closure cl;
        struct bkey *k;

        bch_keylist_init(&keylist);

        if (btree_check_reserve(b, NULL))
                return 0;

        memset(new_nodes, 0, sizeof(new_nodes));
        closure_init_stack(&cl);

        while (nodes < GC_MERGE_NODES && !IS_ERR_OR_NULL(r[nodes].b))
                keys += r[nodes++].keys;

        blocks = btree_default_blocks(b->c) * 2 / 3;

        if (nodes < 2 ||
            __set_blocks(b->keys.set[0].data, keys,
                         block_bytes(b->c)) > blocks * (nodes - 1))
                return 0;

        for (i = 0; i < nodes; i++) {
                new_nodes[i] = btree_node_alloc_replacement(r[i].b, NULL);
                if (IS_ERR_OR_NULL(new_nodes[i]))
                        goto out_nocoalesce;
        }

        /*
         * We have to check the reserve here, after we've allocated our new
         * nodes, to make sure the insert below will succeed - we also check
         * before as an optimization to potentially avoid a bunch of expensive
         * allocs/sorts
         */
        if (btree_check_reserve(b, NULL))
                goto out_nocoalesce;

        for (i = 0; i < nodes; i++)
                mutex_lock(&new_nodes[i]->write_lock);

        for (i = nodes - 1; i > 0; --i) {
                struct bset *n1 = btree_bset_first(new_nodes[i]);
                struct bset *n2 = btree_bset_first(new_nodes[i - 1]);
                struct bkey *k, *last = NULL;

                keys = 0;

                if (i > 1) {
                        for (k = n2->start;
                             k < bset_bkey_last(n2);
                             k = bkey_next(k)) {
                                if (__set_blocks(n1, n1->keys + keys +
                                                 bkey_u64s(k),
                                                 block_bytes(b->c)) > blocks)
                                        break;

                                last = k;
                                keys += bkey_u64s(k);
                        }
                } else {
                        /*
                         * Last node we're not getting rid of - we're getting
                         * rid of the node at r[0]. Have to try and fit all of
                         * the remaining keys into this node; we can't ensure
                         * they will always fit due to rounding and variable
                         * length keys (shouldn't be possible in practice,
                         * though)
                         */
                        if (__set_blocks(n1, n1->keys + n2->keys,
                                         block_bytes(b->c)) >
                            btree_blocks(new_nodes[i]))
                                goto out_nocoalesce;

                        keys = n2->keys;
                        /* Take the key of the node we're getting rid of */
                        last = &r->b->key;
                }

                BUG_ON(__set_blocks(n1, n1->keys + keys, block_bytes(b->c)) >
                       btree_blocks(new_nodes[i]));

                if (last)
                        bkey_copy_key(&new_nodes[i]->key, last);

                memcpy(bset_bkey_last(n1),
                       n2->start,
                       (void *) bset_bkey_idx(n2, keys) - (void *) n2->start);

                n1->keys += keys;
                r[i].keys = n1->keys;

                memmove(n2->start,
                        bset_bkey_idx(n2, keys),
                        (void *) bset_bkey_last(n2) -
                        (void *) bset_bkey_idx(n2, keys));

                n2->keys -= keys;

                if (__bch_keylist_realloc(&keylist,
                                          bkey_u64s(&new_nodes[i]->key)))
                        goto out_nocoalesce;

                bch_btree_node_write(new_nodes[i], &cl);
                bch_keylist_add(&keylist, &new_nodes[i]->key);
        }

        for (i = 0; i < nodes; i++)
                mutex_unlock(&new_nodes[i]->write_lock);

        closure_sync(&cl);

        /* We emptied out this node */
        BUG_ON(btree_bset_first(new_nodes[0])->keys);
        btree_node_free(new_nodes[0]);
        rw_unlock(true, new_nodes[0]);
        new_nodes[0] = NULL;

        for (i = 0; i < nodes; i++) {
                if (__bch_keylist_realloc(&keylist, bkey_u64s(&r[i].b->key)))
                        goto out_nocoalesce;

                make_btree_freeing_key(r[i].b, keylist.top);
                bch_keylist_push(&keylist);
        }

        bch_btree_insert_node(b, op, &keylist, NULL, NULL);
        BUG_ON(!bch_keylist_empty(&keylist));

        for (i = 0; i < nodes; i++) {
                btree_node_free(r[i].b);
                rw_unlock(true, r[i].b);

                r[i].b = new_nodes[i];
        }

        memmove(r, r + 1, sizeof(r[0]) * (nodes - 1));
        r[nodes - 1].b = ERR_PTR(-EINTR);

        trace_bcache_btree_gc_coalesce(nodes);
        gc->nodes--;

        bch_keylist_free(&keylist);

        /* Invalidated our iterator */
        return -EINTR;

out_nocoalesce:
        closure_sync(&cl);
        bch_keylist_free(&keylist);

        while ((k = bch_keylist_pop(&keylist)))
                if (!bkey_cmp(k, &ZERO_KEY))
                        atomic_dec(&b->c->prio_blocked);

        for (i = 0; i < nodes; i++)
                if (!IS_ERR_OR_NULL(new_nodes[i])) {
                        btree_node_free(new_nodes[i]);
                        rw_unlock(true, new_nodes[i]);
                }
        return 0;
}

static int btree_gc_rewrite_node(struct btree *b, struct btree_op *op,
                                 struct btree *replace)
{
        struct keylist keys;
        struct btree *n;

        if (btree_check_reserve(b, NULL))
                return 0;

        n = btree_node_alloc_replacement(replace, NULL);

        /* recheck reserve after allocating replacement node */
        if (btree_check_reserve(b, NULL)) {
                btree_node_free(n);
                rw_unlock(true, n);
                return 0;
        }

        bch_btree_node_write_sync(n);

        bch_keylist_init(&keys);
        bch_keylist_add(&keys, &n->key);

        make_btree_freeing_key(replace, keys.top);
        bch_keylist_push(&keys);

        bch_btree_insert_node(b, op, &keys, NULL, NULL);
        BUG_ON(!bch_keylist_empty(&keys));

        btree_node_free(replace);
        rw_unlock(true, n);

        /* Invalidated our iterator */
        return -EINTR;
}

static unsigned btree_gc_count_keys(struct btree *b)
{
        struct bkey *k;
        struct btree_iter iter;
        unsigned ret = 0;

        for_each_key_filter(&b->keys, k, &iter, bch_ptr_bad)
                ret += bkey_u64s(k);

        return ret;
}

static int btree_gc_recurse(struct btree *b, struct btree_op *op,
                            struct closure *writes, struct gc_stat *gc)
{
        int ret = 0;
        bool should_rewrite;
        struct bkey *k;
        struct btree_iter iter;
        struct gc_merge_info r[GC_MERGE_NODES];
        struct gc_merge_info *i, *last = r + ARRAY_SIZE(r) - 1;

        bch_btree_iter_init(&b->keys, &iter, &b->c->gc_done);

        for (i = r; i < r + ARRAY_SIZE(r); i++)
                i->b = ERR_PTR(-EINTR);

        while (1) {
                k = bch_btree_iter_next_filter(&iter, &b->keys, bch_ptr_bad);
                if (k) {
                        r->b = bch_btree_node_get(b->c, op, k, b->level - 1,
                                                  true, b);
                        if (IS_ERR(r->b)) {
                                ret = PTR_ERR(r->b);
                                break;
                        }

                        r->keys = btree_gc_count_keys(r->b);

                        ret = btree_gc_coalesce(b, op, gc, r);
                        if (ret)
                                break;
                }

                if (!last->b)
                        break;

                if (!IS_ERR(last->b)) {
                        should_rewrite = btree_gc_mark_node(last->b, gc);
                        if (should_rewrite) {
                                ret = btree_gc_rewrite_node(b, op, last->b);
                                if (ret)
                                        break;
                        }

                        if (last->b->level) {
                                ret = btree_gc_recurse(last->b, op, writes, gc);
                                if (ret)
                                        break;
                        }

                        bkey_copy_key(&b->c->gc_done, &last->b->key);

                        /*
                         * Must flush leaf nodes before gc ends, since replace
                         * operations aren't journalled
                         */
                        mutex_lock(&last->b->write_lock);
                        if (btree_node_dirty(last->b))
                                bch_btree_node_write(last->b, writes);
                        mutex_unlock(&last->b->write_lock);
                        rw_unlock(true, last->b);
                }

                memmove(r + 1, r, sizeof(r[0]) * (GC_MERGE_NODES - 1));
                r->b = NULL;

                if (need_resched()) {
                        ret = -EAGAIN;
                        break;
                }
        }

        for (i = r; i < r + ARRAY_SIZE(r); i++)
                if (!IS_ERR_OR_NULL(i->b)) {
                        mutex_lock(&i->b->write_lock);
                        if (btree_node_dirty(i->b))
                                bch_btree_node_write(i->b, writes);
                        mutex_unlock(&i->b->write_lock);
                        rw_unlock(true, i->b);
                }

        return ret;
}

static int bch_btree_gc_root(struct btree *b, struct btree_op *op,
                             struct closure *writes, struct gc_stat *gc)
{
        struct btree *n = NULL;
        int ret = 0;
        bool should_rewrite;

        should_rewrite = btree_gc_mark_node(b, gc);
        if (should_rewrite) {
                n = btree_node_alloc_replacement(b, NULL);

                if (!IS_ERR_OR_NULL(n)) {
                        bch_btree_node_write_sync(n);

                        bch_btree_set_root(n);
                        btree_node_free(b);
                        rw_unlock(true, n);

                        return -EINTR;
                }
        }

        __bch_btree_mark_key(b->c, b->level + 1, &b->key);

        if (b->level) {
                ret = btree_gc_recurse(b, op, writes, gc);
                if (ret)
                        return ret;
        }

        bkey_copy_key(&b->c->gc_done, &b->key);

        return ret;
}

static void btree_gc_start(struct cache_set *c)
{
        struct cache *ca;
        struct bucket *b;
        unsigned i;

        if (!c->gc_mark_valid)
                return;

        mutex_lock(&c->bucket_lock);

        c->gc_mark_valid = 0;
        c->gc_done = ZERO_KEY;

        for_each_cache(ca, c, i)
                for_each_bucket(b, ca) {
                        b->last_gc = b->gen;
                        if (!atomic_read(&b->pin)) {
                                SET_GC_MARK(b, 0);
                                SET_GC_SECTORS_USED(b, 0);
                        }
                }

        mutex_unlock(&c->bucket_lock);
}

static size_t bch_btree_gc_finish(struct cache_set *c)
{
        size_t available = 0;
        struct bucket *b;
        struct cache *ca;
        unsigned i;

        mutex_lock(&c->bucket_lock);

        set_gc_sectors(c);
        c->gc_mark_valid = 1;
        c->need_gc      = 0;

        for (i = 0; i < KEY_PTRS(&c->uuid_bucket); i++)
                SET_GC_MARK(PTR_BUCKET(c, &c->uuid_bucket, i),
                            GC_MARK_METADATA);

        /* don't reclaim buckets to which writeback keys point */
        rcu_read_lock();
        for (i = 0; i < c->nr_uuids; i++) {
                struct bcache_device *d = c->devices[i];
                struct cached_dev *dc;
                struct keybuf_key *w, *n;
                unsigned j;

                if (!d || UUID_FLASH_ONLY(&c->uuids[i]))
                        continue;
                dc = container_of(d, struct cached_dev, disk);

                spin_lock(&dc->writeback_keys.lock);
                rbtree_postorder_for_each_entry_safe(w, n,
                                        &dc->writeback_keys.keys, node)
                        for (j = 0; j < KEY_PTRS(&w->key); j++)
                                SET_GC_MARK(PTR_BUCKET(c, &w->key, j),
                                            GC_MARK_DIRTY);
                spin_unlock(&dc->writeback_keys.lock);
        }
        rcu_read_unlock();

        for_each_cache(ca, c, i) {
                uint64_t *i;

                ca->invalidate_needs_gc = 0;

                for (i = ca->sb.d; i < ca->sb.d + ca->sb.keys; i++)
                        SET_GC_MARK(ca->buckets + *i, GC_MARK_METADATA);

                for (i = ca->prio_buckets;
                     i < ca->prio_buckets + prio_buckets(ca) * 2; i++)
                        SET_GC_MARK(ca->buckets + *i, GC_MARK_METADATA);

                for_each_bucket(b, ca) {
                        c->need_gc      = max(c->need_gc, bucket_gc_gen(b));

                        if (atomic_read(&b->pin))
                                continue;

                        BUG_ON(!GC_MARK(b) && GC_SECTORS_USED(b));

                        if (!GC_MARK(b) || GC_MARK(b) == GC_MARK_RECLAIMABLE)
                                available++;
                }
        }

        mutex_unlock(&c->bucket_lock);
        return available;
}

static void bch_btree_gc(struct cache_set *c)
{
        int ret;
        unsigned long available;
        struct gc_stat stats;
        struct closure writes;
        struct btree_op op;
        uint64_t start_time = local_clock();

        trace_bcache_gc_start(c);

        memset(&stats, 0, sizeof(struct gc_stat));
        closure_init_stack(&writes);
        bch_btree_op_init(&op, SHRT_MAX);

        btree_gc_start(c);

        do {
                ret = btree_root(gc_root, c, &op, &writes, &stats);
                closure_sync(&writes);
                cond_resched();

                if (ret && ret != -EAGAIN)
                        pr_warn("gc failed!");
        } while (ret);

        available = bch_btree_gc_finish(c);
        wake_up_allocators(c);

        bch_time_stats_update(&c->btree_gc_time, start_time);

        stats.key_bytes *= sizeof(uint64_t);
        stats.data      <<= 9;
        stats.in_use    = (c->nbuckets - available) * 100 / c->nbuckets;
        memcpy(&c->gc_stats, &stats, sizeof(struct gc_stat));

        trace_bcache_gc_end(c);

        bch_moving_gc(c);
}

static int bch_gc_thread(void *arg)
{
        struct cache_set *c = arg;
        struct cache *ca;
        unsigned i;

        while (1) {
again:
                bch_btree_gc(c);

                set_current_state(TASK_INTERRUPTIBLE);
                if (kthread_should_stop())
                        break;

                mutex_lock(&c->bucket_lock);

                for_each_cache(ca, c, i)
                        if (ca->invalidate_needs_gc) {
                                mutex_unlock(&c->bucket_lock);
                                set_current_state(TASK_RUNNING);
                                goto again;
                        }

                mutex_unlock(&c->bucket_lock);

                schedule();
        }

        return 0;
}

int bch_gc_thread_start(struct cache_set *c)
{
        c->gc_thread = kthread_create(bch_gc_thread, c, "bcache_gc");
        if (IS_ERR(c->gc_thread))
                return PTR_ERR(c->gc_thread);

        set_task_state(c->gc_thread, TASK_INTERRUPTIBLE);
        return 0;
}

/* Initial partial gc */

static int bch_btree_check_recurse(struct btree *b, struct btree_op *op)
{
        int ret = 0;
        struct bkey *k, *p = NULL;
        struct btree_iter iter;

        for_each_key_filter(&b->keys, k, &iter, bch_ptr_invalid)
                bch_initial_mark_key(b->c, b->level, k);

        bch_initial_mark_key(b->c, b->level + 1, &b->key);

        if (b->level) {
                bch_btree_iter_init(&b->keys, &iter, NULL);

                do {
                        k = bch_btree_iter_next_filter(&iter, &b->keys,
                                                       bch_ptr_bad);
                        if (k)
                                btree_node_prefetch(b, k);

                        if (p)
                                ret = btree(check_recurse, p, b, op);

                        p = k;
                } while (p && !ret);
        }

        return ret;
}

int bch_btree_check(struct cache_set *c)
{
        struct btree_op op;

        bch_btree_op_init(&op, SHRT_MAX);

        return btree_root(check_recurse, c, &op);
}

void bch_initial_gc_finish(struct cache_set *c)
{
        struct cache *ca;
        struct bucket *b;
        unsigned i;

        bch_btree_gc_finish(c);

        mutex_lock(&c->bucket_lock);

        /*
         * We need to put some unused buckets directly on the prio freelist in
         * order to get the allocator thread started - it needs freed buckets in
         * order to rewrite the prios and gens, and it needs to rewrite prios
         * and gens in order to free buckets.
         *
         * This is only safe for buckets that have no live data in them, which
         * there should always be some of.
         */
        for_each_cache(ca, c, i) {
                for_each_bucket(b, ca) {
                        if (fifo_full(&ca->free[RESERVE_PRIO]))
                                break;

                        if (bch_can_invalidate_bucket(ca, b) &&
                            !GC_MARK(b)) {
                                __bch_invalidate_one_bucket(ca, b);
                                fifo_push(&ca->free[RESERVE_PRIO],
                                          b - ca->buckets);
                        }
                }
        }

        mutex_unlock(&c->bucket_lock);
}

/* Btree insertion */

static bool btree_insert_key(struct btree *b, struct bkey *k,
                             struct bkey *replace_key)
{
        unsigned status;

        BUG_ON(bkey_cmp(k, &b->key) > 0);

        status = bch_btree_insert_key(&b->keys, k, replace_key);
        if (status != BTREE_INSERT_STATUS_NO_INSERT) {
                bch_check_keys(&b->keys, "%u for %s", status,
                               replace_key ? "replace" : "insert");

                trace_bcache_btree_insert_key(b, k, replace_key != NULL,
                                              status);
                return true;
        } else
                return false;
}

static size_t insert_u64s_remaining(struct btree *b)
{
        long ret = bch_btree_keys_u64s_remaining(&b->keys);

        /*
         * Might land in the middle of an existing extent and have to split it
         */
        if (b->keys.ops->is_extents)
                ret -= KEY_MAX_U64S;

        return max(ret, 0L);
}

static bool bch_btree_insert_keys(struct btree *b, struct btree_op *op,
                                  struct keylist *insert_keys,
                                  struct bkey *replace_key)
{
        bool ret = false;
        int oldsize = bch_count_data(&b->keys);

        while (!bch_keylist_empty(insert_keys)) {
                struct bkey *k = insert_keys->keys;

                if (bkey_u64s(k) > insert_u64s_remaining(b))
                        break;

                if (bkey_cmp(k, &b->key) <= 0) {
                        if (!b->level)
                                bkey_put(b->c, k);

                        ret |= btree_insert_key(b, k, replace_key);
                        bch_keylist_pop_front(insert_keys);
                } else if (bkey_cmp(&START_KEY(k), &b->key) < 0) {
                        BKEY_PADDED(key) temp;
                        bkey_copy(&temp.key, insert_keys->keys);

                        bch_cut_back(&b->key, &temp.key);
                        bch_cut_front(&b->key, insert_keys->keys);

                        ret |= btree_insert_key(b, &temp.key, replace_key);
                        break;
                } else {
                        break;
                }
        }

        if (!ret)
                op->insert_collision = true;

        BUG_ON(!bch_keylist_empty(insert_keys) && b->level);

        BUG_ON(bch_count_data(&b->keys) < oldsize);
        return ret;
}

static int btree_split(struct btree *b, struct btree_op *op,
                       struct keylist *insert_keys,
                       struct bkey *replace_key)
{
        bool split;
        struct btree *n1, *n2 = NULL, *n3 = NULL;
        uint64_t start_time = local_clock();
        struct closure cl;
        struct keylist parent_keys;

        closure_init_stack(&cl);
        bch_keylist_init(&parent_keys);

        if (btree_check_reserve(b, op)) {
                if (!b->level)
                        return -EINTR;
                else
                        WARN(1, "insufficient reserve for split\n");
        }

        n1 = btree_node_alloc_replacement(b, op);
        if (IS_ERR(n1))
                goto err;

        split = set_blocks(btree_bset_first(n1),
                           block_bytes(n1->c)) > (btree_blocks(b) * 4) / 5;

        if (split) {
                unsigned keys = 0;

                trace_bcache_btree_node_split(b, btree_bset_first(n1)->keys);

                n2 = bch_btree_node_alloc(b->c, op, b->level, b->parent);
                if (IS_ERR(n2))
                        goto err_free1;

                if (!b->parent) {
                        n3 = bch_btree_node_alloc(b->c, op, b->level + 1, NULL);
                        if (IS_ERR(n3))
                                goto err_free2;
                }

                mutex_lock(&n1->write_lock);

                mutex_lock(&n2->write_lock);

                bch_btree_insert_keys(n1, op, insert_keys, replace_key);

                /*
                 * Has to be a linear search because we don't have an auxiliary
                 * search tree yet
                 */

                while (keys < (btree_bset_first(n1)->keys * 3) / 5)
                        keys += bkey_u64s(bset_bkey_idx(btree_bset_first(n1),
                                                        keys));

                bkey_copy_key(&n1->key,
                              bset_bkey_idx(btree_bset_first(n1), keys));
                keys += bkey_u64s(bset_bkey_idx(btree_bset_first(n1), keys));

                btree_bset_first(n2)->keys = btree_bset_first(n1)->keys - keys;
                btree_bset_first(n1)->keys = keys;

                memcpy(btree_bset_first(n2)->start,
                       bset_bkey_last(btree_bset_first(n1)),
                       btree_bset_first(n2)->keys * sizeof(uint64_t));

                bkey_copy_key(&n2->key, &b->key);

                bch_keylist_add(&parent_keys, &n2->key);
                bch_btree_node_write(n2, &cl);
                mutex_unlock(&n2->write_lock);
                rw_unlock(true, n2);
        } else {
                trace_bcache_btree_node_compact(b, btree_bset_first(n1)->keys);

                mutex_lock(&n1->write_lock);
                bch_btree_insert_keys(n1, op, insert_keys, replace_key);
        }

        bch_keylist_add(&parent_keys, &n1->key);
        bch_btree_node_write(n1, &cl);
        mutex_unlock(&n1->write_lock);

        if (n3) {
                /* Depth increases, make a new root */
                mutex_lock(&n3->write_lock);
                bkey_copy_key(&n3->key, &MAX_KEY);
                bch_btree_insert_keys(n3, op, &parent_keys, NULL);
                bch_btree_node_write(n3, &cl);
                mutex_unlock(&n3->write_lock);

                closure_sync(&cl);
                bch_btree_set_root(n3);
                rw_unlock(true, n3);
        } else if (!b->parent) {
                /* Root filled up but didn't need to be split */
                closure_sync(&cl);
                bch_btree_set_root(n1);
        } else {
                /* Split a non root node */
                closure_sync(&cl);
                make_btree_freeing_key(b, parent_keys.top);
                bch_keylist_push(&parent_keys);

                bch_btree_insert_node(b->parent, op, &parent_keys, NULL, NULL);
                BUG_ON(!bch_keylist_empty(&parent_keys));
        }

        btree_node_free(b);
        rw_unlock(true, n1);

        bch_time_stats_update(&b->c->btree_split_time, start_time);

        return 0;
err_free2:
        bkey_put(b->c, &n2->key);
        btree_node_free(n2);
        rw_unlock(true, n2);
err_free1:
        bkey_put(b->c, &n1->key);
        btree_node_free(n1);
        rw_unlock(true, n1);
err:
        WARN(1, "bcache: btree split failed (level %u)", b->level);

        if (n3 == ERR_PTR(-EAGAIN) ||
            n2 == ERR_PTR(-EAGAIN) ||
            n1 == ERR_PTR(-EAGAIN))
                return -EAGAIN;

        return -ENOMEM;
}

static int bch_btree_insert_node(struct btree *b, struct btree_op *op,
                                 struct keylist *insert_keys,
                                 atomic_t *journal_ref,
                                 struct bkey *replace_key)
{
        struct closure cl;

        BUG_ON(b->level && replace_key);

        closure_init_stack(&cl);

        mutex_lock(&b->write_lock);

        if (write_block(b) != btree_bset_last(b) &&
            b->keys.last_set_unwritten)
                bch_btree_init_next(b); /* just wrote a set */

        if (bch_keylist_nkeys(insert_keys) > insert_u64s_remaining(b)) {
                mutex_unlock(&b->write_lock);
                goto split;
        }

        BUG_ON(write_block(b) != btree_bset_last(b));

        if (bch_btree_insert_keys(b, op, insert_keys, replace_key)) {
                if (!b->level)
                        bch_btree_leaf_dirty(b, journal_ref);
                else
                        bch_btree_node_write(b, &cl);
        }

        mutex_unlock(&b->write_lock);

        /* wait for btree node write if necessary, after unlock */
        closure_sync(&cl);

        return 0;
split:
        if (current->bio_list) {
                op->lock = b->c->root->level + 1;
                return -EAGAIN;
        } else if (op->lock <= b->c->root->level) {
                op->lock = b->c->root->level + 1;
                return -EINTR;
        } else {
                /* Invalidated all iterators */
                int ret = btree_split(b, op, insert_keys, replace_key);

                if (bch_keylist_empty(insert_keys))
                        return 0;
                else if (!ret)
                        return -EINTR;
                return ret;
        }
}

int bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
                               struct bkey *check_key)
{
        int ret = -EINTR;
        uint64_t btree_ptr = b->key.ptr[0];
        unsigned long seq = b->seq;
        struct keylist insert;
        bool upgrade = op->lock == -1;

        bch_keylist_init(&insert);

        if (upgrade) {
                rw_unlock(false, b);
                rw_lock(true, b, b->level);

                if (b->key.ptr[0] != btree_ptr ||
                   b->seq != seq + 1) {
                       op->lock = b->level;
                        goto out;
               }
        }

        SET_KEY_PTRS(check_key, 1);
        get_random_bytes(&check_key->ptr[0], sizeof(uint64_t));

        SET_PTR_DEV(check_key, 0, PTR_CHECK_DEV);

        bch_keylist_add(&insert, check_key);

        ret = bch_btree_insert_node(b, op, &insert, NULL, NULL);

        BUG_ON(!ret && !bch_keylist_empty(&insert));
out:
        if (upgrade)
                downgrade_write(&b->lock);
        return ret;
}

struct btree_insert_op {
        struct btree_op op;
        struct keylist  *keys;
        atomic_t        *journal_ref;
        struct bkey     *replace_key;
};

static int btree_insert_fn(struct btree_op *b_op, struct btree *b)
{
        struct btree_insert_op *op = container_of(b_op,
                                        struct btree_insert_op, op);

        int ret = bch_btree_insert_node(b, &op->op, op->keys,
                                        op->journal_ref, op->replace_key);
        if (ret && !bch_keylist_empty(op->keys))
                return ret;
        else
                return MAP_DONE;
}

int bch_btree_insert(struct cache_set *c, struct keylist *keys,
                     atomic_t *journal_ref, struct bkey *replace_key)
{
        struct btree_insert_op op;
        int ret = 0;

        BUG_ON(current->bio_list);
        BUG_ON(bch_keylist_empty(keys));

        bch_btree_op_init(&op.op, 0);
        op.keys         = keys;
        op.journal_ref  = journal_ref;
        op.replace_key  = replace_key;

        while (!ret && !bch_keylist_empty(keys)) {
                op.op.lock = 0;
                ret = bch_btree_map_leaf_nodes(&op.op, c,
                                               &START_KEY(keys->keys),
                                               btree_insert_fn);
        }

        if (ret) {
                struct bkey *k;

                pr_err("error %i", ret);

                while ((k = bch_keylist_pop(keys)))
                        bkey_put(c, k);
        } else if (op.op.insert_collision)
                ret = -ESRCH;

        return ret;
}

void bch_btree_set_root(struct btree *b)
{
        unsigned i;
        struct closure cl;

        closure_init_stack(&cl);

        trace_bcache_btree_set_root(b);

        BUG_ON(!b->written);

        for (i = 0; i < KEY_PTRS(&b->key); i++)
                BUG_ON(PTR_BUCKET(b->c, &b->key, i)->prio != BTREE_PRIO);

        mutex_lock(&b->c->bucket_lock);
        list_del_init(&b->list);
        mutex_unlock(&b->c->bucket_lock);

        b->c->root = b;

        bch_journal_meta(b->c, &cl);
        closure_sync(&cl);
}

/* Map across nodes or keys */

static int bch_btree_map_nodes_recurse(struct btree *b, struct btree_op *op,
                                       struct bkey *from,
                                       btree_map_nodes_fn *fn, int flags)
{
        int ret = MAP_CONTINUE;

        if (b->level) {
                struct bkey *k;
                struct btree_iter iter;

                bch_btree_iter_init(&b->keys, &iter, from);

                while ((k = bch_btree_iter_next_filter(&iter, &b->keys,
                                                       bch_ptr_bad))) {
                        ret = btree(map_nodes_recurse, k, b,
                                    op, from, fn, flags);
                        from = NULL;

                        if (ret != MAP_CONTINUE)
                                return ret;
                }
        }

        if (!b->level || flags == MAP_ALL_NODES)
                ret = fn(op, b);

        return ret;
}

int __bch_btree_map_nodes(struct btree_op *op, struct cache_set *c,
                          struct bkey *from, btree_map_nodes_fn *fn, int flags)
{
        return btree_root(map_nodes_recurse, c, op, from, fn, flags);
}

static int bch_btree_map_keys_recurse(struct btree *b, struct btree_op *op,
                                      struct bkey *from, btree_map_keys_fn *fn,
                                      int flags)
{
        int ret = MAP_CONTINUE;
        struct bkey *k;
        struct btree_iter iter;

        bch_btree_iter_init(&b->keys, &iter, from);

        while ((k = bch_btree_iter_next_filter(&iter, &b->keys, bch_ptr_bad))) {
                ret = !b->level
                        ? fn(op, b, k)
                        : btree(map_keys_recurse, k, b, op, from, fn, flags);
                from = NULL;

                if (ret != MAP_CONTINUE)
                        return ret;
        }

        if (!b->level && (flags & MAP_END_KEY))
                ret = fn(op, b, &KEY(KEY_INODE(&b->key),
                                     KEY_OFFSET(&b->key), 0));

        return ret;
}

int bch_btree_map_keys(struct btree_op *op, struct cache_set *c,
                       struct bkey *from, btree_map_keys_fn *fn, int flags)
{
        return btree_root(map_keys_recurse, c, op, from, fn, flags);
}

/* Keybuf code */

static inline int keybuf_cmp(struct keybuf_key *l, struct keybuf_key *r)
{
        /* Overlapping keys compare equal */
        if (bkey_cmp(&l->key, &START_KEY(&r->key)) <= 0)
                return -1;
        if (bkey_cmp(&START_KEY(&l->key), &r->key) >= 0)
                return 1;
        return 0;
}

static inline int keybuf_nonoverlapping_cmp(struct keybuf_key *l,
                                            struct keybuf_key *r)
{
        return clamp_t(int64_t, bkey_cmp(&l->key, &r->key), -1, 1);
}

struct refill {
        struct btree_op op;
        unsigned        nr_found;
        struct keybuf   *buf;
        struct bkey     *end;
        keybuf_pred_fn  *pred;
};

static int refill_keybuf_fn(struct btree_op *op, struct btree *b,
                            struct bkey *k)
{
        struct refill *refill = container_of(op, struct refill, op);
        struct keybuf *buf = refill->buf;
        int ret = MAP_CONTINUE;

        if (bkey_cmp(k, refill->end) >= 0) {
                ret = MAP_DONE;
                goto out;
        }

        if (!KEY_SIZE(k)) /* end key */
                goto out;

        if (refill->pred(buf, k)) {
                struct keybuf_key *w;

                spin_lock(&buf->lock);

                w = array_alloc(&buf->freelist);
                if (!w) {
                        spin_unlock(&buf->lock);
                        return MAP_DONE;
                }

                w->private = NULL;
                bkey_copy(&w->key, k);

                if (RB_INSERT(&buf->keys, w, node, keybuf_cmp))
                        array_free(&buf->freelist, w);
                else
                        refill->nr_found++;

                if (array_freelist_empty(&buf->freelist))
                        ret = MAP_DONE;

                spin_unlock(&buf->lock);
        }
out:
        buf->last_scanned = *k;
        return ret;
}

void bch_refill_keybuf(struct cache_set *c, struct keybuf *buf,
                       struct bkey *end, keybuf_pred_fn *pred)
{
        struct bkey start = buf->last_scanned;
        struct refill refill;

        cond_resched();

        bch_btree_op_init(&refill.op, -1);
        refill.nr_found = 0;
        refill.buf      = buf;
        refill.end      = end;
        refill.pred     = pred;

        bch_btree_map_keys(&refill.op, c, &buf->last_scanned,
                           refill_keybuf_fn, MAP_END_KEY);

        trace_bcache_keyscan(refill.nr_found,
                             KEY_INODE(&start), KEY_OFFSET(&start),
                             KEY_INODE(&buf->last_scanned),
                             KEY_OFFSET(&buf->last_scanned));

        spin_lock(&buf->lock);

        if (!RB_EMPTY_ROOT(&buf->keys)) {
                struct keybuf_key *w;
                w = RB_FIRST(&buf->keys, struct keybuf_key, node);
                buf->start      = START_KEY(&w->key);

                w = RB_LAST(&buf->keys, struct keybuf_key, node);
                buf->end        = w->key;
        } else {
                buf->start      = MAX_KEY;
                buf->end        = MAX_KEY;
        }

        spin_unlock(&buf->lock);
}

static void __bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w)
{
        rb_erase(&w->node, &buf->keys);
        array_free(&buf->freelist, w);
}

void bch_keybuf_del(struct keybuf *buf, struct keybuf_key *w)
{
        spin_lock(&buf->lock);
        __bch_keybuf_del(buf, w);
        spin_unlock(&buf->lock);
}

bool bch_keybuf_check_overlapping(struct keybuf *buf, struct bkey *start,
                                  struct bkey *end)
{
        bool ret = false;
        struct keybuf_key *p, *w, s;
        s.key = *start;

        if (bkey_cmp(end, &buf->start) <= 0 ||
            bkey_cmp(start, &buf->end) >= 0)
                return false;

        spin_lock(&buf->lock);
        w = RB_GREATER(&buf->keys, s, node, keybuf_nonoverlapping_cmp);

        while (w && bkey_cmp(&START_KEY(&w->key), end) < 0) {
                p = w;
                w = RB_NEXT(w, node);

                if (p->private)
                        ret = true;
                else
                        __bch_keybuf_del(buf, p);
        }

        spin_unlock(&buf->lock);
        return ret;
}

struct keybuf_key *bch_keybuf_next(struct keybuf *buf)
{
        struct keybuf_key *w;
        spin_lock(&buf->lock);

        w = RB_FIRST(&buf->keys, struct keybuf_key, node);

        while (w && w->private)
                w = RB_NEXT(w, node);

        if (w)
                w->private = ERR_PTR(-EINTR);

        spin_unlock(&buf->lock);
        return w;
}

struct keybuf_key *bch_keybuf_next_rescan(struct cache_set *c,
                                          struct keybuf *buf,
                                          struct bkey *end,
                                          keybuf_pred_fn *pred)
{
        struct keybuf_key *ret;

        while (1) {
                ret = bch_keybuf_next(buf);
                if (ret)
                        break;

                if (bkey_cmp(&buf->last_scanned, end) >= 0) {
                        pr_debug("scan finished");
                        break;
                }

                bch_refill_keybuf(c, buf, end, pred);
        }

        return ret;
}

void bch_keybuf_init(struct keybuf *buf)
{
        buf->last_scanned       = MAX_KEY;
        buf->keys               = RB_ROOT;

        spin_lock_init(&buf->lock);
        array_allocator_init(&buf->freelist);
}