/*
   * 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);

  	bio_free_pages(b->bio);

  	__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
  ");

  	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)