bcache in userspace; userspace fsck

1 files changed, 898 insertions, 0 deletions

diff --git a/libbcache/btree_gc.c b/libbcache/btree_gc.c
new file mode 100644
index 0000000..8417187
--- /dev/null
+++ b/libbcache/btree_gc.c
@@ -0,0 +1,898 @@
+/*
+ * Copyright (C) 2010 Kent Overstreet <kent.overstreet@gmail.com>
+ * Copyright (C) 2014 Datera Inc.
+ */
+
+#include "bcache.h"
+#include "alloc.h"
+#include "bkey_methods.h"
+#include "btree_locking.h"
+#include "btree_update.h"
+#include "btree_io.h"
+#include "btree_gc.h"
+#include "buckets.h"
+#include "clock.h"
+#include "debug.h"
+#include "error.h"
+#include "extents.h"
+#include "journal.h"
+#include "keylist.h"
+#include "move.h"
+#include "writeback.h"
+
+#include <linux/slab.h>
+#include <linux/bitops.h>
+#include <linux/freezer.h>
+#include <linux/kthread.h>
+#include <linux/rcupdate.h>
+#include <trace/events/bcache.h>
+
+struct range_checks {
+	struct range_level {
+		struct bpos	min;
+		struct bpos	max;
+	}			l[BTREE_MAX_DEPTH];
+	unsigned		depth;
+};
+
+static void btree_node_range_checks_init(struct range_checks *r, unsigned depth)
+{
+	unsigned i;
+
+	for (i = 0; i < BTREE_MAX_DEPTH; i++)
+		r->l[i].min = r->l[i].max = POS_MIN;
+	r->depth = depth;
+}
+
+static void btree_node_range_checks(struct cache_set *c, struct btree *b,
+				    struct range_checks *r)
+{
+	struct range_level *l = &r->l[b->level];
+
+	struct bpos expected_min = bkey_cmp(l->min, l->max)
+		? btree_type_successor(b->btree_id, l->max)
+		: l->max;
+
+	cache_set_inconsistent_on(bkey_cmp(b->data->min_key,
+					   expected_min), c,
+		"btree node has incorrect min key: %llu:%llu != %llu:%llu",
+		b->data->min_key.inode,
+		b->data->min_key.offset,
+		expected_min.inode,
+		expected_min.offset);
+
+	l->max = b->data->max_key;
+
+	if (b->level > r->depth) {
+		l = &r->l[b->level - 1];
+
+		cache_set_inconsistent_on(bkey_cmp(b->data->min_key,
+						   l->min), c,
+			"btree node min doesn't match min of child nodes: %llu:%llu != %llu:%llu",
+			b->data->min_key.inode,
+			b->data->min_key.offset,
+			l->min.inode,
+			l->min.offset);
+
+		cache_set_inconsistent_on(bkey_cmp(b->data->max_key,
+						   l->max), c,
+			"btree node max doesn't match max of child nodes: %llu:%llu != %llu:%llu",
+			b->data->max_key.inode,
+			b->data->max_key.offset,
+			l->max.inode,
+			l->max.offset);
+
+		if (bkey_cmp(b->data->max_key, POS_MAX))
+			l->min = l->max =
+				btree_type_successor(b->btree_id,
+						     b->data->max_key);
+	}
+}
+
+u8 bch_btree_key_recalc_oldest_gen(struct cache_set *c, struct bkey_s_c k)
+{
+	const struct bch_extent_ptr *ptr;
+	struct cache *ca;
+	u8 max_stale = 0;
+
+	if (bkey_extent_is_data(k.k)) {
+		struct bkey_s_c_extent e = bkey_s_c_to_extent(k);
+
+		rcu_read_lock();
+
+		extent_for_each_online_device(c, e, ptr, ca) {
+			size_t b = PTR_BUCKET_NR(ca, ptr);
+
+			if (__gen_after(ca->oldest_gens[b], ptr->gen))
+				ca->oldest_gens[b] = ptr->gen;
+
+			max_stale = max(max_stale, ptr_stale(ca, ptr));
+		}
+
+		rcu_read_unlock();
+	}
+
+	return max_stale;
+}
+
+/*
+ * For runtime mark and sweep:
+ */
+u8 __bch_btree_mark_key(struct cache_set *c, enum bkey_type type,
+			struct bkey_s_c k)
+{
+	switch (type) {
+	case BKEY_TYPE_BTREE:
+		bch_gc_mark_key(c, k, c->sb.btree_node_size, true);
+		return 0;
+	case BKEY_TYPE_EXTENTS:
+		bch_gc_mark_key(c, k, k.k->size, false);
+		return bch_btree_key_recalc_oldest_gen(c, k);
+	default:
+		BUG();
+	}
+}
+
+static u8 btree_mark_key(struct cache_set *c, struct btree *b,
+			 struct bkey_s_c k)
+{
+	return __bch_btree_mark_key(c, btree_node_type(b), k);
+}
+
+static bool btree_gc_mark_node(struct cache_set *c, struct btree *b)
+{
+	if (btree_node_has_ptrs(b)) {
+		struct btree_node_iter iter;
+		struct bkey unpacked;
+		struct bkey_s_c k;
+		u8 stale = 0;
+
+		for_each_btree_node_key_unpack(b, k, &iter,
+					       btree_node_is_extents(b),
+					       &unpacked) {
+			bkey_debugcheck(c, b, k);
+			stale = max(stale, btree_mark_key(c, b, k));
+		}
+
+		if (btree_gc_rewrite_disabled(c))
+			return false;
+
+		if (stale > 10)
+			return true;
+	}
+
+	if (btree_gc_always_rewrite(c))
+		return true;
+
+	return false;
+}
+
+static inline void __gc_pos_set(struct cache_set *c, struct gc_pos new_pos)
+{
+	write_seqcount_begin(&c->gc_pos_lock);
+	c->gc_pos = new_pos;
+	write_seqcount_end(&c->gc_pos_lock);
+}
+
+static inline void gc_pos_set(struct cache_set *c, struct gc_pos new_pos)
+{
+	BUG_ON(gc_pos_cmp(new_pos, c->gc_pos) <= 0);
+	__gc_pos_set(c, new_pos);
+}
+
+static int bch_gc_btree(struct cache_set *c, enum btree_id btree_id)
+{
+	struct btree_iter iter;
+	struct btree *b;
+	bool should_rewrite;
+	struct range_checks r;
+	unsigned depth = btree_id == BTREE_ID_EXTENTS ? 0 : 1;
+	int ret;
+
+	/*
+	 * if expensive_debug_checks is on, run range_checks on all leaf nodes:
+	 */
+	if (expensive_debug_checks(c))
+		depth = 0;
+
+	btree_node_range_checks_init(&r, depth);
+
+	for_each_btree_node(&iter, c, btree_id, POS_MIN, depth, b) {
+		btree_node_range_checks(c, b, &r);
+
+		bch_verify_btree_nr_keys(b);
+
+		should_rewrite = btree_gc_mark_node(c, b);
+
+		gc_pos_set(c, gc_pos_btree_node(b));
+
+		if (should_rewrite)
+			bch_btree_node_rewrite(&iter, b, NULL);
+
+		bch_btree_iter_cond_resched(&iter);
+	}
+	ret = bch_btree_iter_unlock(&iter);
+	if (ret)
+		return ret;
+
+	mutex_lock(&c->btree_root_lock);
+
+	b = c->btree_roots[btree_id].b;
+	__bch_btree_mark_key(c, BKEY_TYPE_BTREE, bkey_i_to_s_c(&b->key));
+	gc_pos_set(c, gc_pos_btree_root(b->btree_id));
+
+	mutex_unlock(&c->btree_root_lock);
+	return 0;
+}
+
+static void bch_mark_allocator_buckets(struct cache_set *c)
+{
+	struct cache *ca;
+	struct open_bucket *ob;
+	size_t i, j, iter;
+	unsigned ci;
+
+	for_each_cache(ca, c, ci) {
+		spin_lock(&ca->freelist_lock);
+
+		fifo_for_each_entry(i, &ca->free_inc, iter)
+			bch_mark_alloc_bucket(ca, &ca->buckets[i], true);
+
+		for (j = 0; j < RESERVE_NR; j++)
+			fifo_for_each_entry(i, &ca->free[j], iter)
+				bch_mark_alloc_bucket(ca, &ca->buckets[i], true);
+
+		spin_unlock(&ca->freelist_lock);
+	}
+
+	for (ob = c->open_buckets;
+	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets);
+	     ob++) {
+		const struct bch_extent_ptr *ptr;
+
+		mutex_lock(&ob->lock);
+		rcu_read_lock();
+		open_bucket_for_each_online_device(c, ob, ptr, ca)
+			bch_mark_alloc_bucket(ca, PTR_BUCKET(ca, ptr), true);
+		rcu_read_unlock();
+		mutex_unlock(&ob->lock);
+	}
+}
+
+/*
+ * Mark non btree metadata - prios, journal
+ */
+static void bch_mark_metadata(struct cache_set *c)
+{
+	struct cache *ca;
+	unsigned i;
+
+	for_each_cache(ca, c, i) {
+		unsigned j;
+		u64 *i;
+
+		for (j = 0; j < bch_nr_journal_buckets(ca->disk_sb.sb); j++)
+			bch_mark_metadata_bucket(ca,
+				&ca->buckets[journal_bucket(ca->disk_sb.sb, j)],
+				true);
+
+		spin_lock(&ca->prio_buckets_lock);
+
+		for (i = ca->prio_buckets;
+		     i < ca->prio_buckets + prio_buckets(ca) * 2; i++)
+			bch_mark_metadata_bucket(ca, &ca->buckets[*i], true);
+
+		spin_unlock(&ca->prio_buckets_lock);
+	}
+}
+
+/* Also see bch_pending_btree_node_free_insert_done() */
+static void bch_mark_pending_btree_node_frees(struct cache_set *c)
+{
+	struct bucket_stats_cache_set stats = { 0 };
+	struct btree_interior_update *as;
+	struct pending_btree_node_free *d;
+
+	mutex_lock(&c->btree_interior_update_lock);
+	gc_pos_set(c, gc_phase(GC_PHASE_PENDING_DELETE));
+
+	for_each_pending_btree_node_free(c, as, d)
+		if (d->index_update_done)
+			__bch_gc_mark_key(c, bkey_i_to_s_c(&d->key),
+					  c->sb.btree_node_size, true,
+					  &stats);
+	/*
+	 * Don't apply stats - pending deletes aren't tracked in
+	 * cache_set_stats:
+	 */
+
+	mutex_unlock(&c->btree_interior_update_lock);
+}
+
+/**
+ * bch_gc - recompute bucket marks and oldest_gen, rewrite btree nodes
+ */
+void bch_gc(struct cache_set *c)
+{
+	struct cache *ca;
+	struct bucket *g;
+	struct bucket_mark new;
+	u64 start_time = local_clock();
+	unsigned i;
+	int cpu;
+
+	/*
+	 * Walk _all_ references to buckets, and recompute them:
+	 *
+	 * Order matters here:
+	 *  - Concurrent GC relies on the fact that we have a total ordering for
+	 *    everything that GC walks - see  gc_will_visit_node(),
+	 *    gc_will_visit_root()
+	 *
+	 *  - also, references move around in the course of index updates and
+	 *    various other crap: everything needs to agree on the ordering
+	 *    references are allowed to move around in - e.g., we're allowed to
+	 *    start with a reference owned by an open_bucket (the allocator) and
+	 *    move it to the btree, but not the reverse.
+	 *
+	 *    This is necessary to ensure that gc doesn't miss references that
+	 *    move around - if references move backwards in the ordering GC
+	 *    uses, GC could skip past them
+	 */
+
+	if (test_bit(CACHE_SET_GC_FAILURE, &c->flags))
+		return;
+
+	trace_bcache_gc_start(c);
+
+	/*
+	 * Do this before taking gc_lock - bch_disk_reservation_get() blocks on
+	 * gc_lock if sectors_available goes to 0:
+	 */
+	bch_recalc_sectors_available(c);
+
+	down_write(&c->gc_lock);
+
+	lg_global_lock(&c->bucket_stats_lock);
+
+	/*
+	 * Indicates to buckets code that gc is now in progress - done under
+	 * bucket_stats_lock to avoid racing with bch_mark_key():
+	 */
+	__gc_pos_set(c, GC_POS_MIN);
+
+	/* Save a copy of the existing bucket stats while we recompute them: */
+	for_each_cache(ca, c, i) {
+		ca->bucket_stats_cached = __bch_bucket_stats_read_cache(ca);
+		for_each_possible_cpu(cpu) {
+			struct bucket_stats_cache *p =
+				per_cpu_ptr(ca->bucket_stats_percpu, cpu);
+			memset(p, 0, sizeof(*p));
+		}
+	}
+
+	c->bucket_stats_cached = __bch_bucket_stats_read_cache_set(c);
+	for_each_possible_cpu(cpu) {
+		struct bucket_stats_cache_set *p =
+			per_cpu_ptr(c->bucket_stats_percpu, cpu);
+
+		memset(p->s, 0, sizeof(p->s));
+		p->persistent_reserved = 0;
+	}
+
+	lg_global_unlock(&c->bucket_stats_lock);
+
+	/* Clear bucket marks: */
+	for_each_cache(ca, c, i)
+		for_each_bucket(g, ca) {
+			bucket_cmpxchg(g, new, ({
+				new.owned_by_allocator	= 0;
+				new.is_metadata		= 0;
+				new.cached_sectors	= 0;
+				new.dirty_sectors	= 0;
+			}));
+			ca->oldest_gens[g - ca->buckets] = new.gen;
+		}
+
+	/* Walk allocator's references: */
+	bch_mark_allocator_buckets(c);
+
+	/* Walk btree: */
+	while (c->gc_pos.phase < (int) BTREE_ID_NR) {
+		int ret = c->btree_roots[c->gc_pos.phase].b
+			? bch_gc_btree(c, (int) c->gc_pos.phase)
+			: 0;
+
+		if (ret) {
+			bch_err(c, "btree gc failed: %d", ret);
+			set_bit(CACHE_SET_GC_FAILURE, &c->flags);
+			up_write(&c->gc_lock);
+			return;
+		}
+
+		gc_pos_set(c, gc_phase(c->gc_pos.phase + 1));
+	}
+
+	bch_mark_metadata(c);
+	bch_mark_pending_btree_node_frees(c);
+	bch_writeback_recalc_oldest_gens(c);
+
+	for_each_cache(ca, c, i)
+		atomic_long_set(&ca->saturated_count, 0);
+
+	/* Indicates that gc is no longer in progress: */
+	gc_pos_set(c, gc_phase(GC_PHASE_DONE));
+
+	up_write(&c->gc_lock);
+	trace_bcache_gc_end(c);
+	bch_time_stats_update(&c->btree_gc_time, start_time);
+
+	/*
+	 * Wake up allocator in case it was waiting for buckets
+	 * because of not being able to inc gens
+	 */
+	for_each_cache(ca, c, i)
+		bch_wake_allocator(ca);
+}
+
+/* Btree coalescing */
+
+static void recalc_packed_keys(struct btree *b)
+{
+	struct bkey_packed *k;
+
+	memset(&b->nr, 0, sizeof(b->nr));
+
+	BUG_ON(b->nsets != 1);
+
+	for (k =  btree_bkey_first(b, b->set);
+	     k != btree_bkey_last(b, b->set);
+	     k = bkey_next(k))
+		btree_keys_account_key_add(&b->nr, 0, k);
+}
+
+static void bch_coalesce_nodes(struct btree *old_nodes[GC_MERGE_NODES],
+			       struct btree_iter *iter)
+{
+	struct btree *parent = iter->nodes[old_nodes[0]->level + 1];
+	struct cache_set *c = iter->c;
+	unsigned i, nr_old_nodes, nr_new_nodes, u64s = 0;
+	unsigned blocks = btree_blocks(c) * 2 / 3;
+	struct btree *new_nodes[GC_MERGE_NODES];
+	struct btree_interior_update *as;
+	struct btree_reserve *res;
+	struct keylist keylist;
+	struct bkey_format_state format_state;
+	struct bkey_format new_format;
+
+	memset(new_nodes, 0, sizeof(new_nodes));
+	bch_keylist_init(&keylist, NULL, 0);
+
+	/* Count keys that are not deleted */
+	for (i = 0; i < GC_MERGE_NODES && old_nodes[i]; i++)
+		u64s += old_nodes[i]->nr.live_u64s;
+
+	nr_old_nodes = nr_new_nodes = i;
+
+	/* Check if all keys in @old_nodes could fit in one fewer node */
+	if (nr_old_nodes <= 1 ||
+	    __set_blocks(old_nodes[0]->data,
+			 DIV_ROUND_UP(u64s, nr_old_nodes - 1),
+			 block_bytes(c)) > blocks)
+		return;
+
+	res = bch_btree_reserve_get(c, parent, nr_old_nodes,
+				    BTREE_INSERT_NOFAIL|
+				    BTREE_INSERT_USE_RESERVE,
+				    NULL);
+	if (IS_ERR(res)) {
+		trace_bcache_btree_gc_coalesce_fail(c,
+				BTREE_GC_COALESCE_FAIL_RESERVE_GET);
+		return;
+	}
+
+	if (bch_keylist_realloc(&keylist, NULL, 0,
+			(BKEY_U64s + BKEY_EXTENT_U64s_MAX) * nr_old_nodes)) {
+		trace_bcache_btree_gc_coalesce_fail(c,
+				BTREE_GC_COALESCE_FAIL_KEYLIST_REALLOC);
+		goto out;
+	}
+
+	/* Find a format that all keys in @old_nodes can pack into */
+	bch_bkey_format_init(&format_state);
+
+	for (i = 0; i < nr_old_nodes; i++)
+		__bch_btree_calc_format(&format_state, old_nodes[i]);
+
+	new_format = bch_bkey_format_done(&format_state);
+
+	/* Check if repacking would make any nodes too big to fit */
+	for (i = 0; i < nr_old_nodes; i++)
+		if (!bch_btree_node_format_fits(c, old_nodes[i], &new_format)) {
+			trace_bcache_btree_gc_coalesce_fail(c,
+					BTREE_GC_COALESCE_FAIL_FORMAT_FITS);
+			goto out;
+		}
+
+	trace_bcache_btree_gc_coalesce(c, parent, nr_old_nodes);
+
+	as = bch_btree_interior_update_alloc(c);
+
+	for (i = 0; i < nr_old_nodes; i++)
+		bch_btree_interior_update_will_free_node(c, as, old_nodes[i]);
+
+	/* Repack everything with @new_format and sort down to one bset */
+	for (i = 0; i < nr_old_nodes; i++)
+		new_nodes[i] = __btree_node_alloc_replacement(c, old_nodes[i],
+							      new_format, res);
+
+	/*
+	 * Conceptually we concatenate the nodes together and slice them
+	 * up at different boundaries.
+	 */
+	for (i = nr_new_nodes - 1; i > 0; --i) {
+		struct btree *n1 = new_nodes[i];
+		struct btree *n2 = new_nodes[i - 1];
+
+		struct bset *s1 = btree_bset_first(n1);
+		struct bset *s2 = btree_bset_first(n2);
+		struct bkey_packed *k, *last = NULL;
+
+		/* Calculate how many keys from @n2 we could fit inside @n1 */
+		u64s = 0;
+
+		for (k = s2->start;
+		     k < bset_bkey_last(s2) &&
+		     __set_blocks(n1->data, le16_to_cpu(s1->u64s) + u64s + k->u64s,
+				  block_bytes(c)) <= blocks;
+		     k = bkey_next(k)) {
+			last = k;
+			u64s += k->u64s;
+		}
+
+		if (u64s == le16_to_cpu(s2->u64s)) {
+			/* n2 fits entirely in n1 */
+			n1->key.k.p = n1->data->max_key = n2->data->max_key;
+
+			memcpy_u64s(bset_bkey_last(s1),
+				    s2->start,
+				    le16_to_cpu(s2->u64s));
+			le16_add_cpu(&s1->u64s, le16_to_cpu(s2->u64s));
+
+			set_btree_bset_end(n1, n1->set);
+
+			six_unlock_write(&n2->lock);
+			bch_btree_node_free_never_inserted(c, n2);
+			six_unlock_intent(&n2->lock);
+
+			memmove(new_nodes + i - 1,
+				new_nodes + i,
+				sizeof(new_nodes[0]) * (nr_new_nodes - i));
+			new_nodes[--nr_new_nodes] = NULL;
+		} else if (u64s) {
+			/* move part of n2 into n1 */
+			n1->key.k.p = n1->data->max_key =
+				bkey_unpack_pos(n1, last);
+
+			n2->data->min_key =
+				btree_type_successor(iter->btree_id,
+						     n1->data->max_key);
+
+			memcpy_u64s(bset_bkey_last(s1),
+				    s2->start, u64s);
+			le16_add_cpu(&s1->u64s, u64s);
+
+			memmove(s2->start,
+				bset_bkey_idx(s2, u64s),
+				(le16_to_cpu(s2->u64s) - u64s) * sizeof(u64));
+			s2->u64s = cpu_to_le16(le16_to_cpu(s2->u64s) - u64s);
+
+			set_btree_bset_end(n1, n1->set);
+			set_btree_bset_end(n2, n2->set);
+		}
+	}
+
+	for (i = 0; i < nr_new_nodes; i++) {
+		struct btree *n = new_nodes[i];
+
+		recalc_packed_keys(n);
+		btree_node_reset_sib_u64s(n);
+
+		bch_btree_build_aux_trees(n);
+		six_unlock_write(&n->lock);
+
+		bch_btree_node_write(c, n, &as->cl, SIX_LOCK_intent, -1);
+	}
+
+	/*
+	 * The keys for the old nodes get deleted. We don't want to insert keys
+	 * that compare equal to the keys for the new nodes we'll also be
+	 * inserting - we can't because keys on a keylist must be strictly
+	 * greater than the previous keys, and we also don't need to since the
+	 * key for the new node will serve the same purpose (overwriting the key
+	 * for the old node).
+	 */
+	for (i = 0; i < nr_old_nodes; i++) {
+		struct bkey_i delete;
+		unsigned j;
+
+		for (j = 0; j < nr_new_nodes; j++)
+			if (!bkey_cmp(old_nodes[i]->key.k.p,
+				      new_nodes[j]->key.k.p))
+				goto next;
+
+		bkey_init(&delete.k);
+		delete.k.p = old_nodes[i]->key.k.p;
+		bch_keylist_add_in_order(&keylist, &delete);
+next:
+		i = i;
+	}
+
+	/*
+	 * Keys for the new nodes get inserted: bch_btree_insert_keys() only
+	 * does the lookup once and thus expects the keys to be in sorted order
+	 * so we have to make sure the new keys are correctly ordered with
+	 * respect to the deleted keys added in the previous loop
+	 */
+	for (i = 0; i < nr_new_nodes; i++)
+		bch_keylist_add_in_order(&keylist, &new_nodes[i]->key);
+
+	/* Insert the newly coalesced nodes */
+	bch_btree_insert_node(parent, iter, &keylist, res, as);
+
+	BUG_ON(!bch_keylist_empty(&keylist));
+
+	BUG_ON(iter->nodes[old_nodes[0]->level] != old_nodes[0]);
+
+	BUG_ON(!bch_btree_iter_node_replace(iter, new_nodes[0]));
+
+	for (i = 0; i < nr_new_nodes; i++)
+		btree_open_bucket_put(c, new_nodes[i]);
+
+	/* Free the old nodes and update our sliding window */
+	for (i = 0; i < nr_old_nodes; i++) {
+		bch_btree_node_free_inmem(iter, old_nodes[i]);
+		six_unlock_intent(&old_nodes[i]->lock);
+
+		/*
+		 * the index update might have triggered a split, in which case
+		 * the nodes we coalesced - the new nodes we just created -
+		 * might not be sibling nodes anymore - don't add them to the
+		 * sliding window (except the first):
+		 */
+		if (!i) {
+			old_nodes[i] = new_nodes[i];
+		} else {
+			old_nodes[i] = NULL;
+			if (new_nodes[i])
+				six_unlock_intent(&new_nodes[i]->lock);
+		}
+	}
+out:
+	bch_keylist_free(&keylist, NULL);
+	bch_btree_reserve_put(c, res);
+}
+
+static int bch_coalesce_btree(struct cache_set *c, enum btree_id btree_id)
+{
+	struct btree_iter iter;
+	struct btree *b;
+	unsigned i;
+
+	/* Sliding window of adjacent btree nodes */
+	struct btree *merge[GC_MERGE_NODES];
+	u32 lock_seq[GC_MERGE_NODES];
+
+	/*
+	 * XXX: We don't have a good way of positively matching on sibling nodes
+	 * that have the same parent - this code works by handling the cases
+	 * where they might not have the same parent, and is thus fragile. Ugh.
+	 *
+	 * Perhaps redo this to use multiple linked iterators?
+	 */
+	memset(merge, 0, sizeof(merge));
+
+	__for_each_btree_node(&iter, c, btree_id, POS_MIN, 0, b, U8_MAX) {
+		memmove(merge + 1, merge,
+			sizeof(merge) - sizeof(merge[0]));
+		memmove(lock_seq + 1, lock_seq,
+			sizeof(lock_seq) - sizeof(lock_seq[0]));
+
+		merge[0] = b;
+
+		for (i = 1; i < GC_MERGE_NODES; i++) {
+			if (!merge[i] ||
+			    !six_relock_intent(&merge[i]->lock, lock_seq[i]))
+				break;
+
+			if (merge[i]->level != merge[0]->level) {
+				six_unlock_intent(&merge[i]->lock);
+				break;
+			}
+		}
+		memset(merge + i, 0, (GC_MERGE_NODES - i) * sizeof(merge[0]));
+
+		bch_coalesce_nodes(merge, &iter);
+
+		for (i = 1; i < GC_MERGE_NODES && merge[i]; i++) {
+			lock_seq[i] = merge[i]->lock.state.seq;
+			six_unlock_intent(&merge[i]->lock);
+		}
+
+		lock_seq[0] = merge[0]->lock.state.seq;
+
+		if (test_bit(CACHE_SET_GC_STOPPING, &c->flags)) {
+			bch_btree_iter_unlock(&iter);
+			return -ESHUTDOWN;
+		}
+
+		bch_btree_iter_cond_resched(&iter);
+
+		/*
+		 * If the parent node wasn't relocked, it might have been split
+		 * and the nodes in our sliding window might not have the same
+		 * parent anymore - blow away the sliding window:
+		 */
+		if (iter.nodes[iter.level + 1] &&
+		    !btree_node_intent_locked(&iter, iter.level + 1))
+			memset(merge + 1, 0,
+			       (GC_MERGE_NODES - 1) * sizeof(merge[0]));
+	}
+	return bch_btree_iter_unlock(&iter);
+}
+
+/**
+ * bch_coalesce - coalesce adjacent nodes with low occupancy
+ */
+void bch_coalesce(struct cache_set *c)
+{
+	u64 start_time;
+	enum btree_id id;
+
+	if (btree_gc_coalesce_disabled(c))
+		return;
+
+	if (test_bit(CACHE_SET_GC_FAILURE, &c->flags))
+		return;
+
+	down_read(&c->gc_lock);
+	trace_bcache_gc_coalesce_start(c);
+	start_time = local_clock();
+
+	for (id = 0; id < BTREE_ID_NR; id++) {
+		int ret = c->btree_roots[id].b
+			? bch_coalesce_btree(c, id)
+			: 0;
+
+		if (ret) {
+			if (ret != -ESHUTDOWN)
+				bch_err(c, "btree coalescing failed: %d", ret);
+			set_bit(CACHE_SET_GC_FAILURE, &c->flags);
+			return;
+		}
+	}
+
+	bch_time_stats_update(&c->btree_coalesce_time, start_time);
+	trace_bcache_gc_coalesce_end(c);
+	up_read(&c->gc_lock);
+}
+
+static int bch_gc_thread(void *arg)
+{
+	struct cache_set *c = arg;
+	struct io_clock *clock = &c->io_clock[WRITE];
+	unsigned long last = atomic_long_read(&clock->now);
+	unsigned last_kick = atomic_read(&c->kick_gc);
+
+	set_freezable();
+
+	while (1) {
+		unsigned long next = last + c->capacity / 16;
+
+		while (atomic_long_read(&clock->now) < next) {
+			set_current_state(TASK_INTERRUPTIBLE);
+
+			if (kthread_should_stop()) {
+				__set_current_state(TASK_RUNNING);
+				return 0;
+			}
+
+			if (atomic_read(&c->kick_gc) != last_kick) {
+				__set_current_state(TASK_RUNNING);
+				break;
+			}
+
+			bch_io_clock_schedule_timeout(clock, next);
+			try_to_freeze();
+		}
+
+		last = atomic_long_read(&clock->now);
+		last_kick = atomic_read(&c->kick_gc);
+
+		bch_gc(c);
+		bch_coalesce(c);
+
+		debug_check_no_locks_held();
+	}
+
+	return 0;
+}
+
+void bch_gc_thread_stop(struct cache_set *c)
+{
+	set_bit(CACHE_SET_GC_STOPPING, &c->flags);
+
+	if (!IS_ERR_OR_NULL(c->gc_thread))
+		kthread_stop(c->gc_thread);
+}
+
+int bch_gc_thread_start(struct cache_set *c)
+{
+	clear_bit(CACHE_SET_GC_STOPPING, &c->flags);
+
+	c->gc_thread = kthread_create(bch_gc_thread, c, "bcache_gc");
+	if (IS_ERR(c->gc_thread))
+		return PTR_ERR(c->gc_thread);
+
+	wake_up_process(c->gc_thread);
+	return 0;
+}
+
+/* Initial GC computes bucket marks during startup */
+
+static void bch_initial_gc_btree(struct cache_set *c, enum btree_id id)
+{
+	struct btree_iter iter;
+	struct btree *b;
+	struct range_checks r;
+
+	btree_node_range_checks_init(&r, 0);
+
+	if (!c->btree_roots[id].b)
+		return;
+
+	/*
+	 * We have to hit every btree node before starting journal replay, in
+	 * order for the journal seq blacklist machinery to work:
+	 */
+	for_each_btree_node(&iter, c, id, POS_MIN, 0, b) {
+		btree_node_range_checks(c, b, &r);
+
+		if (btree_node_has_ptrs(b)) {
+			struct btree_node_iter node_iter;
+			struct bkey unpacked;
+			struct bkey_s_c k;
+
+			for_each_btree_node_key_unpack(b, k, &node_iter,
+						       btree_node_is_extents(b),
+						       &unpacked)
+				btree_mark_key(c, b, k);
+		}
+
+		bch_btree_iter_cond_resched(&iter);
+	}
+
+	bch_btree_iter_unlock(&iter);
+
+	__bch_btree_mark_key(c, BKEY_TYPE_BTREE,
+			     bkey_i_to_s_c(&c->btree_roots[id].b->key));
+}
+
+int bch_initial_gc(struct cache_set *c, struct list_head *journal)
+{
+	enum btree_id id;
+
+	if (journal) {
+		for (id = 0; id < BTREE_ID_NR; id++)
+			bch_initial_gc_btree(c, id);
+
+		bch_journal_mark(c, journal);
+	}
+
+	bch_mark_metadata(c);
+
+	gc_pos_set(c, gc_phase(GC_PHASE_DONE));
+	set_bit(CACHE_SET_INITIAL_GC_DONE, &c->flags);
+
+	return 0;
+}