/*
 * 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 "request.h"
#include "writeback.h"

#include <linux/slab.h>
#include <linux/bitops.h>
#include <linux/hash.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.
 *
 * Make sure all allocations get charged to the root cgroup
 *
 * Plugging?
 *
 * If data write is less than hard sector size of ssd, round up offset in open
 * bucket to the next whole sector
 *
 * Also lookup by cgroup in get_open_bucket()
 *
 * 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
 */

static const char * const op_types[] = {
        "insert", "replace"
};

static const char *op_type(struct btree_op *op)
{
        return op_types[op->type];
}

#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))

struct workqueue_struct *bch_gc_wq;
static struct workqueue_struct *btree_io_wq;

void bch_btree_op_init_stack(struct btree_op *op)
{
        memset(op, 0, sizeof(struct btree_op));
        closure_init_stack(&op->cl);
        op->lock = -1;
        bch_keylist_init(&op->keys);
}

/* Btree key manipulation */

static void bkey_put(struct cache_set *c, struct bkey *k, int level)
{
        if ((level && KEY_OFFSET(k)) || !level)
                __bkey_put(c, k);
}

/* 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 = end(i);

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

static void bch_btree_node_read_done(struct btree *b)
{
        const char *err = "bad btree header";
        struct bset *i = b->sets[0].data;
        struct btree_iter *iter;

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

        if (!i->seq)
                goto err;

        for (;
             b->written < btree_blocks(b) && i->seq == b->sets[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, b->c) > btree_blocks(b))
                        goto err;

                err = "bad magic";
                if (i->magic != bset_magic(b->c))
                        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->sets[0].data && !i->keys)
                        goto err;

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

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

        err = "corrupted btree";
        for (i = write_block(b);
             index(i, b) < btree_blocks(b);
             i = ((void *) i) + block_bytes(b->c))
                if (i->seq == b->sets[0].data->seq)
                        goto err;

        bch_btree_sort_and_fix_extents(b, iter);

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

        if (b->written < btree_blocks(b))
                bch_bset_init_next(b);
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 %zu, %u keys",
                            err, PTR_BUCKET_NR(b->c, &b->key, 0),
                            index(i, b), i->keys);
        goto out;
}

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

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_rw      = REQ_META|READ_SYNC;
        bio->bi_size    = KEY_SIZE(&b->key) << 9;
        bio->bi_end_io  = btree_node_read_endio;
        bio->bi_private = &cl;

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

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

        if (!test_bit(BIO_UPTODATE, &bio->bi_flags))
                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);

        spin_lock(&b->c->btree_read_time_lock);
        bch_time_stats_update(&b->c->btree_read_time, start_time);
        spin_unlock(&b->c->btree_read_time_lock);

        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_done(struct closure *cl)
{
        struct btree *b = container_of(cl, struct btree, io.cl);
        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))
                queue_delayed_work(btree_io_wq, &b->work,
                                   msecs_to_jiffies(30000));

        closure_return(cl);
}

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

        __bio_for_each_segment(bv, b->bio, n, 0)
                __free_page(bv->bv_page);

        __btree_node_write_done(cl);
}

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

        if (error)
                set_btree_node_io_error(b);

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

static void do_btree_node_write(struct btree *b)
{
        struct closure *cl = &b->io.cl;
        struct bset *i = b->sets[b->nsets].data;
        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      = &b->io.cl;
        b->bio->bi_rw           = REQ_META|WRITE_SYNC|REQ_FUA;
        b->bio->bi_size         = set_blocks(i, b->c) * block_bytes(b->c);
        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_offset(b, i));

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

                bio_for_each_segment(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);
                __btree_node_write_done(cl);
        }
}

void bch_btree_node_write(struct btree *b, struct closure *parent)
{
        struct bset *i = b->sets[b->nsets].data;

        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(b->sets->data->seq != i->seq);
        bch_check_key_order(b, i);

        cancel_delayed_work(&b->work);

        /* If caller isn't waiting for write, parent refcount is cache set */
        closure_lock(&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);

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

        bch_btree_sort_lazy(b);

        if (b->written < btree_blocks(b))
                bch_bset_init_next(b);
}

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

        rw_lock(true, b, b->level);

        if (btree_node_dirty(b))
                bch_btree_node_write(b, NULL);
        rw_unlock(true, b);
}

static void bch_btree_leaf_dirty(struct btree *b, struct btree_op *op)
{
        struct bset *i = b->sets[b->nsets].data;
        struct btree_write *w = btree_current_write(b);

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

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

        set_btree_node_dirty(b);

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

                if (!w->journal) {
                        w->journal = op->journal;
                        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
 */

static void mca_reinit(struct btree *b)
{
        unsigned i;

        b->flags        = 0;
        b->written      = 0;
        b->nsets        = 0;

        for (i = 0; i < MAX_BSETS; i++)
                b->sets[i].size = 0;
        /*
         * Second loop starts at 1 because b->sets[0]->data is the memory we
         * allocated
         */
        for (i = 1; i < MAX_BSETS; i++)
                b->sets[i].data = NULL;
}

#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->bucket_cache_used - mca_reserve(c))

static void mca_data_free(struct btree *b)
{
        struct bset_tree *t = b->sets;
        BUG_ON(!closure_is_unlocked(&b->io.cl));

        if (bset_prev_bytes(b) < PAGE_SIZE)
                kfree(t->prev);
        else
                free_pages((unsigned long) t->prev,
                           get_order(bset_prev_bytes(b)));

        if (bset_tree_bytes(b) < PAGE_SIZE)
                kfree(t->tree);
        else
                free_pages((unsigned long) t->tree,
                           get_order(bset_tree_bytes(b)));

        free_pages((unsigned long) t->data, b->page_order);

        t->prev = NULL;
        t->tree = NULL;
        t->data = NULL;
        list_move(&b->list, &b->c->btree_cache_freed);
        b->c->bucket_cache_used--;
}

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)
{
        struct bset_tree *t = b->sets;
        BUG_ON(t->data);

        b->page_order = max_t(unsigned,
                              ilog2(b->c->btree_pages),
                              btree_order(k));

        t->data = (void *) __get_free_pages(gfp, b->page_order);
        if (!t->data)
                goto err;

        t->tree = bset_tree_bytes(b) < PAGE_SIZE
                ? kmalloc(bset_tree_bytes(b), gfp)
                : (void *) __get_free_pages(gfp, get_order(bset_tree_bytes(b)));
        if (!t->tree)
                goto err;

        t->prev = bset_prev_bytes(b) < PAGE_SIZE
                ? kmalloc(bset_prev_bytes(b), gfp)
                : (void *) __get_free_pages(gfp, get_order(bset_prev_bytes(b)));
        if (!t->prev)
                goto err;

        list_move(&b->list, &b->c->btree_cache);
        b->c->bucket_cache_used++;
        return;
err:
        mca_data_free(b);
}

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);
        INIT_LIST_HEAD(&b->list);
        INIT_DELAYED_WORK(&b->work, btree_node_write_work);
        b->c = c;
        closure_init_unlocked(&b->io);

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

static int mca_reap(struct btree *b, struct closure *cl, unsigned min_order)
{
        lockdep_assert_held(&b->c->bucket_lock);

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

        if (b->page_order < min_order) {
                rw_unlock(true, b);
                return -ENOMEM;
        }

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

        if (cl && btree_node_dirty(b))
                bch_btree_node_write(b, NULL);

        if (cl)
                closure_wait_event_async(&b->io.wait, cl,
                         atomic_read(&b->io.cl.remaining) == -1);

        if (btree_node_dirty(b) ||
            !closure_is_unlocked(&b->io.cl) ||
            work_pending(&b->work.work)) {
                rw_unlock(true, b);
                return -EAGAIN;
        }

        return 0;
}

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->try_harder)
                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, NULL, 0)) {
                        mca_data_free(b);
                        rw_unlock(true, b);
                        freed++;
                }
        }

        /*
         * Can happen right when we first start up, before we've read in any
         * btree nodes
         */
        if (list_empty(&c->btree_cache))
                goto out;

        for (i = 0; (nr--) && i < c->bucket_cache_used; i++) {
                b = list_first_entry(&c->btree_cache, struct btree, list);
                list_rotate_left(&c->btree_cache);

                if (!b->accessed &&
                    !mca_reap(b, NULL, 0)) {
                        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->try_harder)
                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);
#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;

        /* XXX: doesn't check for errors */

        closure_init_unlocked(&c->gc);

        for (i = 0; i < mca_reserve(c); i++)
                mca_bucket_alloc(c, &ZERO_KEY, GFP_KERNEL);

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

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

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

        if (c->verify_data &&
            c->verify_data->sets[0].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 struct btree *mca_cannibalize(struct cache_set *c, struct bkey *k,
                                     int level, struct closure *cl)
{
        int ret = -ENOMEM;
        struct btree *i;

        trace_bcache_btree_cache_cannibalize(c);

        if (!cl)
                return ERR_PTR(-ENOMEM);

        /*
         * Trying to free up some memory - i.e. reuse some btree nodes - may
         * require initiating IO to flush the dirty part of the node. If we're
         * running under generic_make_request(), that IO will never finish and
         * we would deadlock. Returning -EAGAIN causes the cache lookup code to
         * punt to workqueue and retry.
         */
        if (current->bio_list)
                return ERR_PTR(-EAGAIN);

        if (c->try_harder && c->try_harder != cl) {
                closure_wait_event_async(&c->try_wait, cl, !c->try_harder);
                return ERR_PTR(-EAGAIN);
        }

        c->try_harder = cl;
        c->try_harder_start = local_clock();
retry:
        list_for_each_entry_reverse(i, &c->btree_cache, list) {
                int r = mca_reap(i, cl, btree_order(k));
                if (!r)
                        return i;
                if (r != -ENOMEM)
                        ret = r;
        }

        if (ret == -EAGAIN &&
            closure_blocking(cl)) {
                mutex_unlock(&c->bucket_lock);
                closure_sync(cl);
                mutex_lock(&c->bucket_lock);
                goto retry;
        }

        return ERR_PTR(ret);
}

/*
 * 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.
 */
void bch_cannibalize_unlock(struct cache_set *c, struct closure *cl)
{
        if (c->try_harder == cl) {
                bch_time_stats_update(&c->try_harder_time, c->try_harder_start);
                c->try_harder = NULL;
                __closure_wake_up(&c->try_wait);
        }
}

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

        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, NULL, btree_order(k)))
                        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, NULL, 0)) {
                        mca_data_alloc(b, k, __GFP_NOWARN|GFP_NOIO);
                        if (!b->sets[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->sets->data)
                goto err;
out:
        BUG_ON(!closure_is_unlocked(&b->io.cl));

        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->level        = level;

        mca_reinit(b);

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

        b = mca_cannibalize(c, k, level, cl);
        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, it uses the closure embedded in struct btree_op to wait;
 * if that closure is in non blocking mode, will return -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 bkey *k,
                                 int level, struct btree_op *op)
{
        int i = 0;
        bool write = level <= op->lock;
        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, k, level, &op->cl);
                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->accessed = 1;

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

        for (; i <= b->nsets; i++)
                prefetch(b->sets[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 cache_set *c, struct bkey *k, int level)
{
        struct btree *b;

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

        if (!IS_ERR_OR_NULL(b)) {
                bch_btree_node_read(b);
                rw_unlock(true, b);
        }
}

/* Btree alloc */

static void btree_node_free(struct btree *b, struct btree_op *op)
{
        unsigned i;

        trace_bcache_btree_node_free(b);

        /*
         * The BUG_ON() in btree_node_get() implies that we must have a write
         * lock on parent to free or even invalidate a node
         */
        BUG_ON(op->lock <= b->level);
        BUG_ON(b == b->c->root);

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

        cancel_delayed_work(&b->work);

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

        for (i = 0; i < KEY_PTRS(&b->key); i++) {
                BUG_ON(atomic_read(&PTR_BUCKET(b->c, &b->key, i)->pin));

                bch_inc_gen(PTR_CACHE(b->c, &b->key, i),
                            PTR_BUCKET(b->c, &b->key, i));
        }

        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, int level,
                                   struct closure *cl)
{
        BKEY_PADDED(key) k;
        struct btree *b = ERR_PTR(-EAGAIN);

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

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

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

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

        b->accessed = 1;
        bch_bset_init_next(b);

        mutex_unlock(&c->bucket_lock);

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

        trace_bcache_btree_node_alloc_fail(b);
        return b;
}

static struct btree *btree_node_alloc_replacement(struct btree *b,
                                                  struct closure *cl)
{
        struct btree *n = bch_btree_node_alloc(b->c, b->level, cl);
        if (!IS_ERR_OR_NULL(n))
                bch_btree_sort_into(b, n);

        return n;
}

/* Garbage collection */

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->gc_gen, PTR_GEN(k, i)))
                        g->gc_gen = 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);

                /* guard against overflow */
                SET_GC_SECTORS_USED(g, min_t(unsigned,
                                             GC_SECTORS_USED(g) + KEY_SIZE(k),
                                             (1 << 14) - 1));

                BUG_ON(!GC_SECTORS_USED(g));
        }

        return stale;
}

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

static int btree_gc_mark_node(struct btree *b, unsigned *keys,
                              struct gc_stat *gc)
{
        uint8_t stale = 0;
        unsigned last_dev = -1;
        struct bcache_device *d = NULL;
        struct bkey *k;
        struct btree_iter iter;
        struct bset_tree *t;

        gc->nodes++;

        for_each_key_filter(b, k, &iter, bch_ptr_invalid) {
                if (last_dev != KEY_INODE(k)) {
                        last_dev = KEY_INODE(k);

                        d = KEY_INODE(k) < b->c->nr_uuids
                                ? b->c->devices[last_dev]
                                : NULL;
                }

                stale = max(stale, btree_mark_key(b, k));

                if (bch_ptr_bad(b, k))
                        continue;

                *keys += bkey_u64s(k);

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

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

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

        return stale;
}

static struct btree *btree_gc_alloc(struct btree *b, struct bkey *k,
                                    struct btree_op *op)
{
        /*
         * We block priorities from being written for the duration of garbage
         * collection, so we can't sleep in btree_alloc() ->
         * bch_bucket_alloc_set(), or we'd risk deadlock - so we don't pass it
         * our closure.
         */
        struct btree *n = btree_node_alloc_replacement(b, NULL);

        if (!IS_ERR_OR_NULL(n)) {
                swap(b, n);
                __bkey_put(b->c, &b->key);

                memcpy(k->ptr, b->key.ptr,
                       sizeof(uint64_t) * KEY_PTRS(&b->key));

                btree_node_free(n, op);
                up_write(&n->lock);
        }

        return b;
}

/*
 * Leaving this at 2 until we've got incremental garbage collection done; it
 * could be higher (and has been tested with 4) except that garbage collection
 * could take much longer, adversely affecting latency.
 */
#define GC_MERGE_NODES  2U

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

static void btree_gc_coalesce(struct btree *b, struct btree_op *op,
                              struct gc_stat *gc, struct gc_merge_info *r)
{
        unsigned nodes = 0, keys = 0, blocks;
        int i;

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

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

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

        for (i = nodes - 1; i >= 0; --i) {
                if (r[i].b->written)
                        r[i].b = btree_gc_alloc(r[i].b, r[i].k, op);

                if (r[i].b->written)
                        return;
        }

        for (i = nodes - 1; i > 0; --i) {
                struct bset *n1 = r[i].b->sets->data;
                struct bset *n2 = r[i - 1].b->sets->data;
                struct bkey *k, *last = NULL;

                keys = 0;

                if (i == 1) {
                        /*
                         * 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 + r->keys,
                                         b->c) > btree_blocks(r[i].b))
                                return;

                        keys = n2->keys;
                        last = &r->b->key;
                } else
                        for (k = n2->start;
                             k < end(n2);
                             k = bkey_next(k)) {
                                if (__set_blocks(n1, n1->keys + keys +
                                                 bkey_u64s(k), b->c) > blocks)
                                        break;

                                last = k;
                                keys += bkey_u64s(k);
                        }

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

                if (last) {
                        bkey_copy_key(&r[i].b->key, last);
                        bkey_copy_key(r[i].k, last);
                }

                memcpy(end(n1),
                       n2->start,
                       (void *) node(n2, keys) - (void *) n2->start);

                n1->keys += keys;

                memmove(n2->start,
                        node(n2, keys),
                        (void *) end(n2) - (void *) node(n2, keys));

                n2->keys -= keys;

                r[i].keys       = n1->keys;
                r[i - 1].keys   = n2->keys;
        }

        btree_node_free(r->b, op);
        up_write(&r->b->lock);

        trace_bcache_btree_gc_coalesce(nodes);

        gc->nodes--;
        nodes--;

        memmove(&r[0], &r[1], sizeof(struct gc_merge_info) * nodes);
        memset(&r[nodes], 0, sizeof(struct gc_merge_info));
}

static int btree_gc_recurse(struct btree *b, struct btree_op *op,
                            struct closure *writes, struct gc_stat *gc)
{
        void write(struct btree *r)
        {
                if (!r->written)
                        bch_btree_node_write(r, &op->cl);
                else if (btree_node_dirty(r))
                        bch_btree_node_write(r, writes);

                up_write(&r->lock);
        }

        int ret = 0, stale;
        unsigned i;
        struct gc_merge_info r[GC_MERGE_NODES];

        memset(r, 0, sizeof(r));

        while ((r->k = bch_next_recurse_key(b, &b->c->gc_done))) {
                r->b = bch_btree_node_get(b->c, r->k, b->level - 1, op);

                if (IS_ERR(r->b)) {
                        ret = PTR_ERR(r->b);
                        break;
                }

                r->keys = 0;
                stale = btree_gc_mark_node(r->b, &r->keys, gc);

                if (!b->written &&
                    (r->b->level || stale > 10 ||
                     b->c->gc_always_rewrite))
                        r->b = btree_gc_alloc(r->b, r->k, op);

                if (r->b->level)
                        ret = btree_gc_recurse(r->b, op, writes, gc);

                if (ret) {
                        write(r->b);
                        break;
                }

                bkey_copy_key(&b->c->gc_done, r->k);

                if (!b->written)
                        btree_gc_coalesce(b, op, gc, r);

                if (r[GC_MERGE_NODES - 1].b)
                        write(r[GC_MERGE_NODES - 1].b);

                memmove(&r[1], &r[0],
                        sizeof(struct gc_merge_info) * (GC_MERGE_NODES - 1));

                /* When we've got incremental GC working, we'll want to do
                 * if (should_resched())
                 *      return -EAGAIN;
                 */
                cond_resched();
#if 0
                if (need_resched()) {
                        ret = -EAGAIN;
                        break;
                }
#endif
        }

        for (i = 1; i < GC_MERGE_NODES && r[i].b; i++)
                write(r[i].b);

        /* Might have freed some children, must remove their keys */
        if (!b->written)
                bch_btree_sort(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;
        unsigned keys = 0;
        int ret = 0, stale = btree_gc_mark_node(b, &keys, gc);

        if (b->level || stale > 10)
                n = btree_node_alloc_replacement(b, NULL);

        if (!IS_ERR_OR_NULL(n))
                swap(b, n);

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

        if (!b->written || btree_node_dirty(b)) {
                bch_btree_node_write(b, n ? &op->cl : NULL);
        }

        if (!IS_ERR_OR_NULL(n)) {
                closure_sync(&op->cl);
                bch_btree_set_root(b);
                btree_node_free(n, op);
                rw_unlock(true, b);
        }

        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->gc_gen = b->gen;
                        if (!atomic_read(&b->pin)) {
                                SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
                                SET_GC_SECTORS_USED(b, 0);
                        }
                }

        mutex_unlock(&c->bucket_lock);
}

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;

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

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

        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) {
                        b->last_gc      = b->gc_gen;
                        c->need_gc      = max(c->need_gc, bucket_gc_gen(b));

                        if (!atomic_read(&b->pin) &&
                            GC_MARK(b) == GC_MARK_RECLAIMABLE) {
                                available++;
                                if (!GC_SECTORS_USED(b))
                                        bch_bucket_add_unused(ca, b);
                        }
                }
        }

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

static void bch_btree_gc(struct closure *cl)
{
        struct cache_set *c = container_of(cl, struct cache_set, gc.cl);
        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_stack(&op);
        op.lock = SHRT_MAX;

        btree_gc_start(c);

        atomic_inc(&c->prio_blocked);

        ret = btree_root(gc_root, c, &op, &writes, &stats);
        closure_sync(&op.cl);
        closure_sync(&writes);

        if (ret) {
                pr_warn("gc failed!");
                continue_at(cl, bch_btree_gc, bch_gc_wq);
        }

        /* Possibly wait for new UUIDs or whatever to hit disk */
        bch_journal_meta(c, &op.cl);
        closure_sync(&op.cl);

        available = bch_btree_gc_finish(c);

        atomic_dec(&c->prio_blocked);
        wake_up_allocators(c);

        bch_time_stats_update(&c->btree_gc_time, start_time);

        stats.key_bytes *= sizeof(uint64_t);
        stats.dirty     <<= 9;
        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);

        continue_at(cl, bch_moving_gc, bch_gc_wq);
}

void bch_queue_gc(struct cache_set *c)
{
        closure_trylock_call(&c->gc.cl, bch_btree_gc, bch_gc_wq, &c->cl);
}

/* Initial partial gc */

static int bch_btree_check_recurse(struct btree *b, struct btree_op *op,
                                   unsigned long **seen)
{
        int ret;
        unsigned i;
        struct bkey *k;
        struct bucket *g;
        struct btree_iter iter;

        for_each_key_filter(b, k, &iter, bch_ptr_invalid) {
                for (i = 0; i < KEY_PTRS(k); i++) {
                        if (!ptr_available(b->c, k, i))
                                continue;

                        g = PTR_BUCKET(b->c, k, i);

                        if (!__test_and_set_bit(PTR_BUCKET_NR(b->c, k, i),
                                                seen[PTR_DEV(k, i)]) ||
                            !ptr_stale(b->c, k, i)) {
                                g->gen = PTR_GEN(k, i);

                                if (b->level)
                                        g->prio = BTREE_PRIO;
                                else if (g->prio == BTREE_PRIO)
                                        g->prio = INITIAL_PRIO;
                        }
                }

                btree_mark_key(b, k);
        }

        if (b->level) {
                k = bch_next_recurse_key(b, &ZERO_KEY);

                while (k) {
                        struct bkey *p = bch_next_recurse_key(b, k);
                        if (p)
                                btree_node_prefetch(b->c, p, b->level - 1);

                        ret = btree(check_recurse, k, b, op, seen);
                        if (ret)
                                return ret;

                        k = p;
                }
        }

        return 0;
}

int bch_btree_check(struct cache_set *c, struct btree_op *op)
{
        int ret = -ENOMEM;
        unsigned i;
        unsigned long *seen[MAX_CACHES_PER_SET];

        memset(seen, 0, sizeof(seen));

        for (i = 0; c->cache[i]; i++) {
                size_t n = DIV_ROUND_UP(c->cache[i]->sb.nbuckets, 8);
                seen[i] = kmalloc(n, GFP_KERNEL);
                if (!seen[i])
                        goto err;

                /* Disables the seen array until prio_read() uses it too */
                memset(seen[i], 0xFF, n);
        }

        ret = btree_root(check_recurse, c, op, seen);
err:
        for (i = 0; i < MAX_CACHES_PER_SET; i++)
                kfree(seen[i]);
        return ret;
}

/* Btree insertion */

static void shift_keys(struct btree *b, struct bkey *where, struct bkey *insert)
{
        struct bset *i = b->sets[b->nsets].data;

        memmove((uint64_t *) where + bkey_u64s(insert),
                where,
                (void *) end(i) - (void *) where);

        i->keys += bkey_u64s(insert);
        bkey_copy(where, insert);
        bch_bset_fix_lookup_table(b, where);
}

static bool fix_overlapping_extents(struct btree *b,
                                    struct bkey *insert,
                                    struct btree_iter *iter,
                                    struct btree_op *op)
{
        void subtract_dirty(struct bkey *k, uint64_t offset, int sectors)
        {
                if (KEY_DIRTY(k))
                        bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
                                                     offset, -sectors);
        }

        uint64_t old_offset;
        unsigned old_size, sectors_found = 0;

        while (1) {
                struct bkey *k = bch_btree_iter_next(iter);
                if (!k ||
                    bkey_cmp(&START_KEY(k), insert) >= 0)
                        break;

                if (bkey_cmp(k, &START_KEY(insert)) <= 0)
                        continue;

                old_offset = KEY_START(k);
                old_size = KEY_SIZE(k);

                /*
                 * We might overlap with 0 size extents; we can't skip these
                 * because if they're in the set we're inserting to we have to
                 * adjust them so they don't overlap with the key we're
                 * inserting. But we don't want to check them for BTREE_REPLACE
                 * operations.
                 */

                if (op->type == BTREE_REPLACE &&
                    KEY_SIZE(k)) {
                        /*
                         * k might have been split since we inserted/found the
                         * key we're replacing
                         */
                        unsigned i;
                        uint64_t offset = KEY_START(k) -
                                KEY_START(&op->replace);

                        /* But it must be a subset of the replace key */
                        if (KEY_START(k) < KEY_START(&op->replace) ||
                            KEY_OFFSET(k) > KEY_OFFSET(&op->replace))
                                goto check_failed;

                        /* We didn't find a key that we were supposed to */
                        if (KEY_START(k) > KEY_START(insert) + sectors_found)
                                goto check_failed;

                        if (KEY_PTRS(&op->replace) != KEY_PTRS(k))
                                goto check_failed;

                        /* skip past gen */
                        offset <<= 8;

                        BUG_ON(!KEY_PTRS(&op->replace));

                        for (i = 0; i < KEY_PTRS(&op->replace); i++)
                                if (k->ptr[i] != op->replace.ptr[i] + offset)
                                        goto check_failed;

                        sectors_found = KEY_OFFSET(k) - KEY_START(insert);
                }

                if (bkey_cmp(insert, k) < 0 &&
                    bkey_cmp(&START_KEY(insert), &START_KEY(k)) > 0) {
                        /*
                         * We overlapped in the middle of an existing key: that
                         * means we have to split the old key. But we have to do
                         * slightly different things depending on whether the
                         * old key has been written out yet.
                         */

                        struct bkey *top;

                        subtract_dirty(k, KEY_START(insert), KEY_SIZE(insert));

                        if (bkey_written(b, k)) {
                                /*
                                 * We insert a new key to cover the top of the
                                 * old key, and the old key is modified in place
                                 * to represent the bottom split.
                                 *
                                 * It's completely arbitrary whether the new key
                                 * is the top or the bottom, but it has to match
                                 * up with what btree_sort_fixup() does - it
                                 * doesn't check for this kind of overlap, it
                                 * depends on us inserting a new key for the top
                                 * here.
                                 */
                                top = bch_bset_search(b, &b->sets[b->nsets],
                                                      insert);
                                shift_keys(b, top, k);
                        } else {
                                BKEY_PADDED(key) temp;
                                bkey_copy(&temp.key, k);
                                shift_keys(b, k, &temp.key);
                                top = bkey_next(k);
                        }

                        bch_cut_front(insert, top);
                        bch_cut_back(&START_KEY(insert), k);
                        bch_bset_fix_invalidated_key(b, k);
                        return false;
                }

                if (bkey_cmp(insert, k) < 0) {
                        bch_cut_front(insert, k);
                } else {
                        if (bkey_written(b, k) &&
                            bkey_cmp(&START_KEY(insert), &START_KEY(k)) <= 0) {
                                /*
                                 * Completely overwrote, so we don't have to
                                 * invalidate the binary search tree
                                 */
                                bch_cut_front(k, k);
                        } else {
                                __bch_cut_back(&START_KEY(insert), k);
                                bch_bset_fix_invalidated_key(b, k);
                        }
                }

                subtract_dirty(k, old_offset, old_size - KEY_SIZE(k));
        }

check_failed:
        if (op->type == BTREE_REPLACE) {
                if (!sectors_found) {
                        op->insert_collision = true;
                        return true;
                } else if (sectors_found < KEY_SIZE(insert)) {
                        SET_KEY_OFFSET(insert, KEY_OFFSET(insert) -
                                       (KEY_SIZE(insert) - sectors_found));
                        SET_KEY_SIZE(insert, sectors_found);
                }
        }

        return false;
}

static bool btree_insert_key(struct btree *b, struct btree_op *op,
                             struct bkey *k)
{
        struct bset *i = b->sets[b->nsets].data;
        struct bkey *m, *prev;
        unsigned status = BTREE_INSERT_STATUS_INSERT;

        BUG_ON(bkey_cmp(k, &b->key) > 0);
        BUG_ON(b->level && !KEY_PTRS(k));
        BUG_ON(!b->level && !KEY_OFFSET(k));

        if (!b->level) {
                struct btree_iter iter;
                struct bkey search = KEY(KEY_INODE(k), KEY_START(k), 0);

                /*
                 * bset_search() returns the first key that is strictly greater
                 * than the search key - but for back merging, we want to find
                 * the first key that is greater than or equal to KEY_START(k) -
                 * unless KEY_START(k) is 0.
                 */
                if (KEY_OFFSET(&search))
                        SET_KEY_OFFSET(&search, KEY_OFFSET(&search) - 1);

                prev = NULL;
                m = bch_btree_iter_init(b, &iter, &search);

                if (fix_overlapping_extents(b, k, &iter, op))
                        return false;

                while (m != end(i) &&
                       bkey_cmp(k, &START_KEY(m)) > 0)
                        prev = m, m = bkey_next(m);

                if (key_merging_disabled(b->c))
                        goto insert;

                /* prev is in the tree, if we merge we're done */
                status = BTREE_INSERT_STATUS_BACK_MERGE;
                if (prev &&
                    bch_bkey_try_merge(b, prev, k))
                        goto merged;

                status = BTREE_INSERT_STATUS_OVERWROTE;
                if (m != end(i) &&
                    KEY_PTRS(m) == KEY_PTRS(k) && !KEY_SIZE(m))
                        goto copy;

                status = BTREE_INSERT_STATUS_FRONT_MERGE;
                if (m != end(i) &&
                    bch_bkey_try_merge(b, k, m))
                        goto copy;
        } else
                m = bch_bset_search(b, &b->sets[b->nsets], k);

insert: shift_keys(b, m, k);
copy:   bkey_copy(m, k);
merged:
        if (KEY_DIRTY(k))
                bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
                                             KEY_START(k), KEY_SIZE(k));

        bch_check_keys(b, "%u for %s", status, op_type(op));

        if (b->level && !KEY_OFFSET(k))
                btree_current_write(b)->prio_blocked++;

        trace_bcache_btree_insert_key(b, k, op->type, status);

        return true;
}

static bool bch_btree_insert_keys(struct btree *b, struct btree_op *op)
{
        bool ret = false;
        struct bkey *k;
        unsigned oldsize = bch_count_data(b);

        while ((k = bch_keylist_pop(&op->keys))) {
                bkey_put(b->c, k, b->level);
                ret |= btree_insert_key(b, op, k);
        }

        BUG_ON(bch_count_data(b) < oldsize);
        return ret;
}

bool bch_btree_insert_check_key(struct btree *b, struct btree_op *op,
                                   struct bio *bio)
{
        bool ret = false;
        uint64_t btree_ptr = b->key.ptr[0];
        unsigned long seq = b->seq;
        BKEY_PADDED(k) tmp;

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

        if (b->key.ptr[0] != btree_ptr ||
            b->seq != seq + 1 ||
            should_split(b))
                goto out;

        op->replace = KEY(op->inode, bio_end_sector(bio), bio_sectors(bio));

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

        SET_PTR_DEV(&op->replace, 0, PTR_CHECK_DEV);

        bkey_copy(&tmp.k, &op->replace);

        BUG_ON(op->type != BTREE_INSERT);
        BUG_ON(!btree_insert_key(b, op, &tmp.k));
        ret = true;
out:
        downgrade_write(&b->lock);
        return ret;
}

static int btree_split(struct btree *b, struct btree_op *op)
{
        bool split, root = b == b->c->root;
        struct btree *n1, *n2 = NULL, *n3 = NULL;
        uint64_t start_time = local_clock();

        if (b->level)
                set_closure_blocking(&op->cl);

        n1 = btree_node_alloc_replacement(b, &op->cl);
        if (IS_ERR(n1))
                goto err;

        split = set_blocks(n1->sets[0].data, n1->c) > (btree_blocks(b) * 4) / 5;

        if (split) {
                unsigned keys = 0;

                trace_bcache_btree_node_split(b, n1->sets[0].data->keys);

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

                if (root) {
                        n3 = bch_btree_node_alloc(b->c, b->level + 1, &op->cl);
                        if (IS_ERR(n3))
                                goto err_free2;
                }

                bch_btree_insert_keys(n1, op);

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

                while (keys < (n1->sets[0].data->keys * 3) / 5)
                        keys += bkey_u64s(node(n1->sets[0].data, keys));

                bkey_copy_key(&n1->key, node(n1->sets[0].data, keys));
                keys += bkey_u64s(node(n1->sets[0].data, keys));

                n2->sets[0].data->keys = n1->sets[0].data->keys - keys;
                n1->sets[0].data->keys = keys;

                memcpy(n2->sets[0].data->start,
                       end(n1->sets[0].data),
                       n2->sets[0].data->keys * sizeof(uint64_t));

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

                bch_keylist_add(&op->keys, &n2->key);
                bch_btree_node_write(n2, &op->cl);
                rw_unlock(true, n2);
        } else {
                trace_bcache_btree_node_compact(b, n1->sets[0].data->keys);

                bch_btree_insert_keys(n1, op);
        }

        bch_keylist_add(&op->keys, &n1->key);
        bch_btree_node_write(n1, &op->cl);

        if (n3) {
                bkey_copy_key(&n3->key, &MAX_KEY);
                bch_btree_insert_keys(n3, op);
                bch_btree_node_write(n3, &op->cl);

                closure_sync(&op->cl);
                bch_btree_set_root(n3);
                rw_unlock(true, n3);
        } else if (root) {
                op->keys.top = op->keys.bottom;
                closure_sync(&op->cl);
                bch_btree_set_root(n1);
        } else {
                unsigned i;

                bkey_copy(op->keys.top, &b->key);
                bkey_copy_key(op->keys.top, &ZERO_KEY);

                for (i = 0; i < KEY_PTRS(&b->key); i++) {
                        uint8_t g = PTR_BUCKET(b->c, &b->key, i)->gen + 1;

                        SET_PTR_GEN(op->keys.top, i, g);
                }

                bch_keylist_push(&op->keys);
                closure_sync(&op->cl);
                atomic_inc(&b->c->prio_blocked);
        }

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

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

        return 0;
err_free2:
        __bkey_put(n2->c, &n2->key);
        btree_node_free(n2, op);
        rw_unlock(true, n2);
err_free1:
        __bkey_put(n1->c, &n1->key);
        btree_node_free(n1, op);

        rw_unlock(true, n1);
err:
        if (n3 == ERR_PTR(-EAGAIN) ||
            n2 == ERR_PTR(-EAGAIN) ||
            n1 == ERR_PTR(-EAGAIN))
                return -EAGAIN;

        pr_warn("couldn't split");
        return -ENOMEM;
}

static int bch_btree_insert_recurse(struct btree *b, struct btree_op *op,
                                    struct keylist *stack_keys)
{
        if (b->level) {
                int ret;
                struct bkey *insert = op->keys.bottom;
                struct bkey *k = bch_next_recurse_key(b, &START_KEY(insert));

                if (!k) {
                        btree_bug(b, "no key to recurse on at level %i/%i",
                                  b->level, b->c->root->level);

                        op->keys.top = op->keys.bottom;
                        return -EIO;
                }

                if (bkey_cmp(insert, k) > 0) {
                        unsigned i;

                        if (op->type == BTREE_REPLACE) {
                                __bkey_put(b->c, insert);
                                op->keys.top = op->keys.bottom;
                                op->insert_collision = true;
                                return 0;
                        }

                        for (i = 0; i < KEY_PTRS(insert); i++)
                                atomic_inc(&PTR_BUCKET(b->c, insert, i)->pin);

                        bkey_copy(stack_keys->top, insert);

                        bch_cut_back(k, insert);
                        bch_cut_front(k, stack_keys->top);

                        bch_keylist_push(stack_keys);
                }

                ret = btree(insert_recurse, k, b, op, stack_keys);
                if (ret)
                        return ret;
        }

        if (!bch_keylist_empty(&op->keys)) {
                if (should_split(b)) {
                        if (op->lock <= b->c->root->level) {
                                BUG_ON(b->level);
                                op->lock = b->c->root->level + 1;
                                return -EINTR;
                        }
                        return btree_split(b, op);
                }

                BUG_ON(write_block(b) != b->sets[b->nsets].data);

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

        return 0;
}

int bch_btree_insert(struct btree_op *op, struct cache_set *c)
{
        int ret = 0;
        struct keylist stack_keys;

        /*
         * Don't want to block with the btree locked unless we have to,
         * otherwise we get deadlocks with try_harder and between split/gc
         */
        clear_closure_blocking(&op->cl);

        BUG_ON(bch_keylist_empty(&op->keys));
        bch_keylist_copy(&stack_keys, &op->keys);
        bch_keylist_init(&op->keys);

        while (!bch_keylist_empty(&stack_keys) ||
               !bch_keylist_empty(&op->keys)) {
                if (bch_keylist_empty(&op->keys)) {
                        bch_keylist_add(&op->keys,
                                        bch_keylist_pop(&stack_keys));
                        op->lock = 0;
                }

                ret = btree_root(insert_recurse, c, op, &stack_keys);

                if (ret == -EAGAIN) {
                        ret = 0;
                        closure_sync(&op->cl);
                } else if (ret) {
                        struct bkey *k;

                        pr_err("error %i trying to insert key for %s",
                               ret, op_type(op));

                        while ((k = bch_keylist_pop(&stack_keys) ?:
                                    bch_keylist_pop(&op->keys)))
                                bkey_put(c, k, 0);
                }
        }

        bch_keylist_free(&stack_keys);

        if (op->journal)
                atomic_dec_bug(op->journal);
        op->journal = NULL;
        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;
        __bkey_put(b->c, &b->key);

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

/* Cache lookup */

static int submit_partial_cache_miss(struct btree *b, struct btree_op *op,
                                     struct bkey *k)
{
        struct search *s = container_of(op, struct search, op);
        struct bio *bio = &s->bio.bio;
        int ret = 0;

        while (!ret &&
               !op->lookup_done) {
                unsigned sectors = INT_MAX;

                if (KEY_INODE(k) == op->inode) {
                        if (KEY_START(k) <= bio->bi_sector)
                                break;

                        sectors = min_t(uint64_t, sectors,
                                        KEY_START(k) - bio->bi_sector);
                }

                ret = s->d->cache_miss(b, s, bio, sectors);
        }

        return ret;
}

/*
 * Read from a single key, handling the initial cache miss if the key starts in
 * the middle of the bio
 */
static int submit_partial_cache_hit(struct btree *b, struct btree_op *op,
                                    struct bkey *k)
{
        struct search *s = container_of(op, struct search, op);
        struct bio *bio = &s->bio.bio;
        unsigned ptr;
        struct bio *n;

        int ret = submit_partial_cache_miss(b, op, k);
        if (ret || op->lookup_done)
                return ret;

        /* XXX: figure out best pointer - for multiple cache devices */
        ptr = 0;

        PTR_BUCKET(b->c, k, ptr)->prio = INITIAL_PRIO;

        while (!op->lookup_done &&
               KEY_INODE(k) == op->inode &&
               bio->bi_sector < KEY_OFFSET(k)) {
                struct bkey *bio_key;
                sector_t sector = PTR_OFFSET(k, ptr) +
                        (bio->bi_sector - KEY_START(k));
                unsigned sectors = min_t(uint64_t, INT_MAX,
                                         KEY_OFFSET(k) - bio->bi_sector);

                n = bch_bio_split(bio, sectors, GFP_NOIO, s->d->bio_split);
                if (n == bio)
                        op->lookup_done = true;

                bio_key = &container_of(n, struct bbio, bio)->key;

                /*
                 * The bucket we're reading from might be reused while our bio
                 * is in flight, and we could then end up reading the wrong
                 * data.
                 *
                 * We guard against this by checking (in cache_read_endio()) if
                 * the pointer is stale again; if so, we treat it as an error
                 * and reread from the backing device (but we don't pass that
                 * error up anywhere).
                 */

                bch_bkey_copy_single_ptr(bio_key, k, ptr);
                SET_PTR_OFFSET(bio_key, 0, sector);

                n->bi_end_io    = bch_cache_read_endio;
                n->bi_private   = &s->cl;

                __bch_submit_bbio(n, b->c);
        }

        return 0;
}

int bch_btree_search_recurse(struct btree *b, struct btree_op *op)
{
        struct search *s = container_of(op, struct search, op);
        struct bio *bio = &s->bio.bio;

        int ret = 0;
        struct bkey *k;
        struct btree_iter iter;
        bch_btree_iter_init(b, &iter, &KEY(op->inode, bio->bi_sector, 0));

        do {
                k = bch_btree_iter_next_filter(&iter, b, bch_ptr_bad);
                if (!k) {
                        /*
                         * b->key would be exactly what we want, except that
                         * pointers to btree nodes have nonzero size - we
                         * wouldn't go far enough
                         */

                        ret = submit_partial_cache_miss(b, op,
                                        &KEY(KEY_INODE(&b->key),
                                             KEY_OFFSET(&b->key), 0));
                        break;
                }

                ret = b->level
                        ? btree(search_recurse, k, b, op)
                        : submit_partial_cache_hit(b, op, k);
        } while (!ret &&
                 !op->lookup_done);

        return ret;
}

/* 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);
}

static int bch_btree_refill_keybuf(struct btree *b, struct btree_op *op,
                                   struct keybuf *buf, struct bkey *end,
                                   keybuf_pred_fn *pred)
{
        struct btree_iter iter;
        bch_btree_iter_init(b, &iter, &buf->last_scanned);

        while (!array_freelist_empty(&buf->freelist)) {
                struct bkey *k = bch_btree_iter_next_filter(&iter, b,
                                                            bch_ptr_bad);

                if (!b->level) {
                        if (!k) {
                                buf->last_scanned = b->key;
                                break;
                        }

                        buf->last_scanned = *k;
                        if (bkey_cmp(&buf->last_scanned, end) >= 0)
                                break;

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

                                spin_lock(&buf->lock);

                                w = array_alloc(&buf->freelist);

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

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

                                spin_unlock(&buf->lock);
                        }
                } else {
                        if (!k)
                                break;

                        btree(refill_keybuf, k, b, op, buf, end, pred);
                        /*
                         * Might get an error here, but can't really do anything
                         * and it'll get logged elsewhere. Just read what we
                         * can.
                         */

                        if (bkey_cmp(&buf->last_scanned, end) >= 0)
                                break;

                        cond_resched();
                }
        }

        return 0;
}

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 btree_op op;
        bch_btree_op_init_stack(&op);

        cond_resched();

        btree_root(refill_keybuf, c, &op, buf, end, pred);
        closure_sync(&op.cl);

        pr_debug("found %s keys from %llu:%llu to %llu:%llu",
                 RB_EMPTY_ROOT(&buf->keys) ? "no" :
                 array_freelist_empty(&buf->freelist) ? "some" : "a few",
                 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);
}

void bch_btree_exit(void)
{
        if (btree_io_wq)
                destroy_workqueue(btree_io_wq);
        if (bch_gc_wq)
                destroy_workqueue(bch_gc_wq);
}

int __init bch_btree_init(void)
{
        if (!(bch_gc_wq = create_singlethread_workqueue("bch_btree_gc")) ||
            !(btree_io_wq = create_singlethread_workqueue("bch_btree_io")))
                return -ENOMEM;

        return 0;
}