md/bcache/journal.c

// SPDX-License-Identifier: GPL-2.0
/*
 * bcache journalling code, for btree insertions
 *
 * Copyright 2012 Google, Inc.
 */

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

#include <trace/events/bcache.h>

/*
 * Journal replay/recovery:
 *
 * This code is all driven from run_cache_set(); we first read the journal
 * entries, do some other stuff, then we mark all the keys in the journal
 * entries (same as garbage collection would), then we replay them - reinserting
 * them into the cache in precisely the same order as they appear in the
 * journal.
 *
 * We only journal keys that go in leaf nodes, which simplifies things quite a
 * bit.
 */

static void journal_read_endio(struct bio *bio)
{
	struct closure *cl = bio->bi_private;

	closure_put(cl);
}

static int journal_read_bucket(struct cache *ca, struct list_head *list,
			       unsigned int bucket_index)
{
	struct journal_device *ja = &ca->journal;
	struct bio *bio = &ja->bio;

	struct journal_replay *i;
	struct jset *j, *data = ca->set->journal.w[0].data;
	struct closure cl;
	unsigned int len, left, offset = 0;
	int ret = 0;
	sector_t bucket = bucket_to_sector(ca->set, ca->sb.d[bucket_index]);

	closure_init_stack(&cl);

	pr_debug("reading %u\n", bucket_index);

	while (offset < ca->sb.bucket_size) {
reread:		left = ca->sb.bucket_size - offset;
		len = min_t(unsigned int, left, PAGE_SECTORS << JSET_BITS);

		bio_reset(bio, ca->bdev, REQ_OP_READ);
		bio->bi_iter.bi_sector	= bucket + offset;
		bio->bi_iter.bi_size	= len << 9;

		bio->bi_end_io	= journal_read_endio;
		bio->bi_private = &cl;
		bch_bio_map(bio, data);

		closure_bio_submit(ca->set, bio, &cl);
		closure_sync(&cl);

		/* This function could be simpler now since we no longer write
		 * journal entries that overlap bucket boundaries; this means
		 * the start of a bucket will always have a valid journal entry
		 * if it has any journal entries at all.
		 */

		j = data;
		while (len) {
			struct list_head *where;
			size_t blocks, bytes = set_bytes(j);

			if (j->magic != jset_magic(&ca->sb)) {
				pr_debug("%u: bad magic\n", bucket_index);
				return ret;
			}

			if (bytes > left << 9 ||
			    bytes > PAGE_SIZE << JSET_BITS) {
				pr_info("%u: too big, %zu bytes, offset %u\n",
					bucket_index, bytes, offset);
				return ret;
			}

			if (bytes > len << 9)
				goto reread;

			if (j->csum != csum_set(j)) {
				pr_info("%u: bad csum, %zu bytes, offset %u\n",
					bucket_index, bytes, offset);
				return ret;
			}

			blocks = set_blocks(j, block_bytes(ca));

			/*
			 * Nodes in 'list' are in linear increasing order of
			 * i->j.seq, the node on head has the smallest (oldest)
			 * journal seq, the node on tail has the biggest
			 * (latest) journal seq.
			 */

			/*
			 * Check from the oldest jset for last_seq. If
			 * i->j.seq < j->last_seq, it means the oldest jset
			 * in list is expired and useless, remove it from
			 * this list. Otherwise, j is a candidate jset for
			 * further following checks.
			 */
			while (!list_empty(list)) {
				i = list_first_entry(list,
					struct journal_replay, list);
				if (i->j.seq >= j->last_seq)
					break;
				list_del(&i->list);
				kfree(i);
			}

			/* iterate list in reverse order (from latest jset) */
			list_for_each_entry_reverse(i, list, list) {
				if (j->seq == i->j.seq)
					goto next_set;

				/*
				 * if j->seq is less than any i->j.last_seq
				 * in list, j is an expired and useless jset.
				 */
				if (j->seq < i->j.last_seq)
					goto next_set;

				/*
				 * 'where' points to first jset in list which
				 * is elder then j.
				 */
				if (j->seq > i->j.seq) {
					where = &i->list;
					goto add;
				}
			}

			where = list;
add:
			i = kmalloc(offsetof(struct journal_replay, j) +
				    bytes, GFP_KERNEL);
			if (!i)
				return -ENOMEM;
			unsafe_memcpy(&i->j, j, bytes,
				/* "bytes" was calculated by set_bytes() above */);
			/* Add to the location after 'where' points to */
			list_add(&i->list, where);
			ret = 1;

			if (j->seq > ja->seq[bucket_index])
				ja->seq[bucket_index] = j->seq;
next_set:
			offset	+= blocks * ca->sb.block_size;
			len	-= blocks * ca->sb.block_size;
			j = ((void *) j) + blocks * block_bytes(ca);
		}
	}

	return ret;
}

int bch_journal_read(struct cache_set *c, struct list_head *list)
{
#define read_bucket(b)							\
	({								\
		ret = journal_read_bucket(ca, list, b);			\
		__set_bit(b, bitmap);					\
		if (ret < 0)						\
			return ret;					\
		ret;							\
	})

	struct cache *ca = c->cache;
	int ret = 0;
	struct journal_device *ja = &ca->journal;
	DECLARE_BITMAP(bitmap, SB_JOURNAL_BUCKETS);
	unsigned int i, l, r, m;
	uint64_t seq;

	bitmap_zero(bitmap, SB_JOURNAL_BUCKETS);
	pr_debug("%u journal buckets\n", ca->sb.njournal_buckets);

	/*
	 * Read journal buckets ordered by golden ratio hash to quickly
	 * find a sequence of buckets with valid journal entries
	 */
	for (i = 0; i < ca->sb.njournal_buckets; i++) {
		/*
		 * We must try the index l with ZERO first for
		 * correctness due to the scenario that the journal
		 * bucket is circular buffer which might have wrapped
		 */
		l = (i * 2654435769U) % ca->sb.njournal_buckets;

		if (test_bit(l, bitmap))
			break;

		if (read_bucket(l))
			goto bsearch;
	}

	/*
	 * If that fails, check all the buckets we haven't checked
	 * already
	 */
	pr_debug("falling back to linear search\n");

	for_each_clear_bit(l, bitmap, ca->sb.njournal_buckets)
		if (read_bucket(l))
			goto bsearch;

	/* no journal entries on this device? */
	if (l == ca->sb.njournal_buckets)
		goto out;
bsearch:
	BUG_ON(list_empty(list));

	/* Binary search */
	m = l;
	r = find_next_bit(bitmap, ca->sb.njournal_buckets, l + 1);
	pr_debug("starting binary search, l %u r %u\n", l, r);

	while (l + 1 < r) {
		seq = list_entry(list->prev, struct journal_replay,
				 list)->j.seq;

		m = (l + r) >> 1;
		read_bucket(m);

		if (seq != list_entry(list->prev, struct journal_replay,
				      list)->j.seq)
			l = m;
		else
			r = m;
	}

	/*
	 * Read buckets in reverse order until we stop finding more
	 * journal entries
	 */
	pr_debug("finishing up: m %u njournal_buckets %u\n",
		 m, ca->sb.njournal_buckets);
	l = m;

	while (1) {
		if (!l--)
			l = ca->sb.njournal_buckets - 1;

		if (l == m)
			break;

		if (test_bit(l, bitmap))
			continue;

		if (!read_bucket(l))
			break;
	}

	seq = 0;

	for (i = 0; i < ca->sb.njournal_buckets; i++)
		if (ja->seq[i] > seq) {
			seq = ja->seq[i];
			/*
			 * When journal_reclaim() goes to allocate for
			 * the first time, it'll use the bucket after
			 * ja->cur_idx
			 */
			ja->cur_idx = i;
			ja->last_idx = ja->discard_idx = (i + 1) %
				ca->sb.njournal_buckets;

		}

out:
	if (!list_empty(list))
		c->journal.seq = list_entry(list->prev,
					    struct journal_replay,
					    list)->j.seq;

	return 0;
#undef read_bucket
}

void bch_journal_mark(struct cache_set *c, struct list_head *list)
{
	atomic_t p = { 0 };
	struct bkey *k;
	struct journal_replay *i;
	struct journal *j = &c->journal;
	uint64_t last = j->seq;

	/*
	 * journal.pin should never fill up - we never write a journal
	 * entry when it would fill up. But if for some reason it does, we
	 * iterate over the list in reverse order so that we can just skip that
	 * refcount instead of bugging.
	 */

	list_for_each_entry_reverse(i, list, list) {
		BUG_ON(last < i->j.seq);
		i->pin = NULL;

		while (last-- != i->j.seq)
			if (fifo_free(&j->pin) > 1) {
				fifo_push_front(&j->pin, p);
				atomic_set(&fifo_front(&j->pin), 0);
			}

		if (fifo_free(&j->pin) > 1) {
			fifo_push_front(&j->pin, p);
			i->pin = &fifo_front(&j->pin);
			atomic_set(i->pin, 1);
		}

		for (k = i->j.start;
		     k < bset_bkey_last(&i->j);
		     k = bkey_next(k))
			if (!__bch_extent_invalid(c, k)) {
				unsigned int j;

				for (j = 0; j < KEY_PTRS(k); j++)
					if (ptr_available(c, k, j))
						atomic_inc(&PTR_BUCKET(c, k, j)->pin);

				bch_initial_mark_key(c, 0, k);
			}
	}
}

static bool is_discard_enabled(struct cache_set *s)
{
	struct cache *ca = s->cache;

	if (ca->discard)
		return true;

	return false;
}

int bch_journal_replay(struct cache_set *s, struct list_head *list)
{
	int ret = 0, keys = 0, entries = 0;
	struct bkey *k;
	struct journal_replay *i =
		list_entry(list->prev, struct journal_replay, list);

	uint64_t start = i->j.last_seq, end = i->j.seq, n = start;
	struct keylist keylist;

	list_for_each_entry(i, list, list) {
		BUG_ON(i->pin && atomic_read(i->pin) != 1);

		if (n != i->j.seq) {
			if (n == start && is_discard_enabled(s))
				pr_info("journal entries %llu-%llu may be discarded! (replaying %llu-%llu)\n",
					n, i->j.seq - 1, start, end);
			else {
				pr_err("journal entries %llu-%llu missing! (replaying %llu-%llu)\n",
					n, i->j.seq - 1, start, end);
				ret = -EIO;
				goto err;
			}
		}

		for (k = i->j.start;
		     k < bset_bkey_last(&i->j);
		     k = bkey_next(k)) {
			trace_bcache_journal_replay_key(k);

			bch_keylist_init_single(&keylist, k);

			ret = bch_btree_insert(s, &keylist, i->pin, NULL);
			if (ret)
				goto err;

			BUG_ON(!bch_keylist_empty(&keylist));
			keys++;

			cond_resched();
		}

		if (i->pin)
			atomic_dec(i->pin);
		n = i->j.seq + 1;
		entries++;
	}

	pr_info("journal replay done, %i keys in %i entries, seq %llu\n",
		keys, entries, end);
err:
	while (!list_empty(list)) {
		i = list_first_entry(list, struct journal_replay, list);
		list_del(&i->list);
		kfree(i);
	}

	return ret;
}

void bch_journal_space_reserve(struct journal *j)
{
	j->do_reserve = true;
}

/* Journalling */

static void btree_flush_write(struct cache_set *c)
{
	struct btree *b, *t, *btree_nodes[BTREE_FLUSH_NR];
	unsigned int i, nr;
	int ref_nr;
	atomic_t *fifo_front_p, *now_fifo_front_p;
	size_t mask;

	if (c->journal.btree_flushing)
		return;

	spin_lock(&c->journal.flush_write_lock);
	if (c->journal.btree_flushing) {
		spin_unlock(&c->journal.flush_write_lock);
		return;
	}
	c->journal.btree_flushing = true;
	spin_unlock(&c->journal.flush_write_lock);

	/* get the oldest journal entry and check its refcount */
	spin_lock(&c->journal.lock);
	fifo_front_p = &fifo_front(&c->journal.pin);
	ref_nr = atomic_read(fifo_front_p);
	if (ref_nr <= 0) {
		/*
		 * do nothing if no btree node references
		 * the oldest journal entry
		 */
		spin_unlock(&c->journal.lock);
		goto out;
	}
	spin_unlock(&c->journal.lock);

	mask = c->journal.pin.mask;
	nr = 0;
	atomic_long_inc(&c->flush_write);
	memset(btree_nodes, 0, sizeof(btree_nodes));

	mutex_lock(&c->bucket_lock);
	list_for_each_entry_safe_reverse(b, t, &c->btree_cache, list) {
		/*
		 * It is safe to get now_fifo_front_p without holding
		 * c->journal.lock here, because we don't need to know
		 * the exactly accurate value, just check whether the
		 * front pointer of c->journal.pin is changed.
		 */
		now_fifo_front_p = &fifo_front(&c->journal.pin);
		/*
		 * If the oldest journal entry is reclaimed and front
		 * pointer of c->journal.pin changes, it is unnecessary
		 * to scan c->btree_cache anymore, just quit the loop and
		 * flush out what we have already.
		 */
		if (now_fifo_front_p != fifo_front_p)
			break;
		/*
		 * quit this loop if all matching btree nodes are
		 * scanned and record in btree_nodes[] already.
		 */
		ref_nr = atomic_read(fifo_front_p);
		if (nr >= ref_nr)
			break;

		if (btree_node_journal_flush(b))
			pr_err("BUG: flush_write bit should not be set here!\n");

		mutex_lock(&b->write_lock);

		if (!btree_node_dirty(b)) {
			mutex_unlock(&b->write_lock);
			continue;
		}

		if (!btree_current_write(b)->journal) {
			mutex_unlock(&b->write_lock);
			continue;
		}

		/*
		 * Only select the btree node which exactly references
		 * the oldest journal entry.
		 *
		 * If the journal entry pointed by fifo_front_p is
		 * reclaimed in parallel, don't worry:
		 * - the list_for_each_xxx loop will quit when checking
		 *   next now_fifo_front_p.
		 * - If there are matched nodes recorded in btree_nodes[],
		 *   they are clean now (this is why and how the oldest
		 *   journal entry can be reclaimed). These selected nodes
		 *   will be ignored and skipped in the following for-loop.
		 */
		if (((btree_current_write(b)->journal - fifo_front_p) &
		     mask) != 0) {
			mutex_unlock(&b->write_lock);
			continue;
		}

		set_btree_node_journal_flush(b);

		mutex_unlock(&b->write_lock);

		btree_nodes[nr++] = b;
		/*
		 * To avoid holding c->bucket_lock too long time,
		 * only scan for BTREE_FLUSH_NR matched btree nodes
		 * at most. If there are more btree nodes reference
		 * the oldest journal entry, try to flush them next
		 * time when btree_flush_write() is called.
		 */
		if (nr == BTREE_FLUSH_NR)
			break;
	}
	mutex_unlock(&c->bucket_lock);

	for (i = 0; i < nr; i++) {
		b = btree_nodes[i];
		if (!b) {
			pr_err("BUG: btree_nodes[%d] is NULL\n", i);
			continue;
		}

		/* safe to check without holding b->write_lock */
		if (!btree_node_journal_flush(b)) {
			pr_err("BUG: bnode %p: journal_flush bit cleaned\n", b);
			continue;
		}

		mutex_lock(&b->write_lock);
		if (!btree_current_write(b)->journal) {
			clear_bit(BTREE_NODE_journal_flush, &b->flags);
			mutex_unlock(&b->write_lock);
			pr_debug("bnode %p: written by others\n", b);
			continue;
		}

		if (!btree_node_dirty(b)) {
			clear_bit(BTREE_NODE_journal_flush, &b->flags);
			mutex_unlock(&b->write_lock);
			pr_debug("bnode %p: dirty bit cleaned by others\n", b);
			continue;
		}

		__bch_btree_node_write(b, NULL);
		clear_bit(BTREE_NODE_journal_flush, &b->flags);
		mutex_unlock(&b->write_lock);
	}

out:
	spin_lock(&c->journal.flush_write_lock);
	c->journal.btree_flushing = false;
	spin_unlock(&c->journal.flush_write_lock);
}

#define last_seq(j)	((j)->seq - fifo_used(&(j)->pin) + 1)

static void journal_discard_endio(struct bio *bio)
{
	struct journal_device *ja =
		container_of(bio, struct journal_device, discard_bio);
	struct cache *ca = container_of(ja, struct cache, journal);

	atomic_set(&ja->discard_in_flight, DISCARD_DONE);

	closure_wake_up(&ca->set->journal.wait);
	closure_put(&ca->set->cl);
}

static void journal_discard_work(struct work_struct *work)
{
	struct journal_device *ja =
		container_of(work, struct journal_device, discard_work);

	submit_bio(&ja->discard_bio);
}

static void do_journal_discard(struct cache *ca)
{
	struct journal_device *ja = &ca->journal;
	struct bio *bio = &ja->discard_bio;

	if (!ca->discard) {
		ja->discard_idx = ja->last_idx;
		return;
	}

	switch (atomic_read(&ja->discard_in_flight)) {
	case DISCARD_IN_FLIGHT:
		return;

	case DISCARD_DONE:
		ja->discard_idx = (ja->discard_idx + 1) %
			ca->sb.njournal_buckets;

		atomic_set(&ja->discard_in_flight, DISCARD_READY);
		fallthrough;

	case DISCARD_READY:
		if (ja->discard_idx == ja->last_idx)
			return;

		atomic_set(&ja->discard_in_flight, DISCARD_IN_FLIGHT);

		bio_init(bio, ca->bdev, bio->bi_inline_vecs, 1, REQ_OP_DISCARD);
		bio->bi_iter.bi_sector	= bucket_to_sector(ca->set,
						ca->sb.d[ja->discard_idx]);
		bio->bi_iter.bi_size	= bucket_bytes(ca);
		bio->bi_end_io		= journal_discard_endio;

		closure_get(&ca->set->cl);
		INIT_WORK(&ja->discard_work, journal_discard_work);
		queue_work(bch_journal_wq, &ja->discard_work);
	}
}

static unsigned int free_journal_buckets(struct cache_set *c)
{
	struct journal *j = &c->journal;
	struct cache *ca = c->cache;
	struct journal_device *ja = &c->cache->journal;
	unsigned int n;

	/* In case njournal_buckets is not power of 2 */
	if (ja->cur_idx >= ja->discard_idx)
		n = ca->sb.njournal_buckets +  ja->discard_idx - ja->cur_idx;
	else
		n = ja->discard_idx - ja->cur_idx;

	if (n > (1 + j->do_reserve))
		return n - (1 + j->do_reserve);

	return 0;
}

static void journal_reclaim(struct cache_set *c)
{
	struct bkey *k = &c->journal.key;
	struct cache *ca = c->cache;
	uint64_t last_seq;
	struct journal_device *ja = &ca->journal;
	atomic_t p __maybe_unused;

	atomic_long_inc(&c->reclaim);

	while (!atomic_read(&fifo_front(&c->journal.pin)))
		fifo_pop(&c->journal.pin, p);

	last_seq = last_seq(&c->journal);

	/* Update last_idx */

	while (ja->last_idx != ja->cur_idx &&
	       ja->seq[ja->last_idx] < last_seq)
		ja->last_idx = (ja->last_idx + 1) %
			ca->sb.njournal_buckets;

	do_journal_discard(ca);

	if (c->journal.blocks_free)
		goto out;

	if (!free_journal_buckets(c))
		goto out;

	ja->cur_idx = (ja->cur_idx + 1) % ca->sb.njournal_buckets;
	k->ptr[0] = MAKE_PTR(0,
			     bucket_to_sector(c, ca->sb.d[ja->cur_idx]),
			     ca->sb.nr_this_dev);
	atomic_long_inc(&c->reclaimed_journal_buckets);

	bkey_init(k);
	SET_KEY_PTRS(k, 1);
	c->journal.blocks_free = ca->sb.bucket_size >> c->block_bits;

out:
	if (!journal_full(&c->journal))
		__closure_wake_up(&c->journal.wait);
}

void bch_journal_next(struct journal *j)
{
	atomic_t p = { 1 };

	j->cur = (j->cur == j->w)
		? &j->w[1]
		: &j->w[0];

	/*
	 * The fifo_push() needs to happen at the same time as j->seq is
	 * incremented for last_seq() to be calculated correctly
	 */
	BUG_ON(!fifo_push(&j->pin, p));
	atomic_set(&fifo_back(&j->pin), 1);

	j->cur->data->seq	= ++j->seq;
	j->cur->dirty		= false;
	j->cur->need_write	= false;
	j->cur->data->keys	= 0;

	if (fifo_full(&j->pin))
		pr_debug("journal_pin full (%zu)\n", fifo_used(&j->pin));
}

static void journal_write_endio(struct bio *bio)
{
	struct journal_write *w = bio->bi_private;

	cache_set_err_on(bio->bi_status, w->c, "journal io error");
	closure_put(&w->c->journal.io);
}

static CLOSURE_CALLBACK(journal_write);

static CLOSURE_CALLBACK(journal_write_done)
{
	closure_type(j, struct journal, io);
	struct journal_write *w = (j->cur == j->w)
		? &j->w[1]
		: &j->w[0];

	__closure_wake_up(&w->wait);
	continue_at_nobarrier(cl, journal_write, bch_journal_wq);
}

static CLOSURE_CALLBACK(journal_write_unlock)
	__releases(&c->journal.lock)
{
	closure_type(c, struct cache_set, journal.io);

	c->journal.io_in_flight = 0;
	spin_unlock(&c->journal.lock);
}

static CLOSURE_CALLBACK(journal_write_unlocked)
	__releases(c->journal.lock)
{
	closure_type(c, struct cache_set, journal.io);
	struct cache *ca = c->cache;
	struct journal_write *w = c->journal.cur;
	struct bkey *k = &c->journal.key;
	unsigned int i, sectors = set_blocks(w->data, block_bytes(ca)) *
		ca->sb.block_size;

	struct bio *bio;
	struct bio_list list;

	bio_list_init(&list);

	if (!w->need_write) {
		closure_return_with_destructor(cl, journal_write_unlock);
		return;
	} else if (journal_full(&c->journal)) {
		journal_reclaim(c);
		spin_unlock(&c->journal.lock);

		btree_flush_write(c);
		continue_at(cl, journal_write, bch_journal_wq);
		return;
	}

	c->journal.blocks_free -= set_blocks(w->data, block_bytes(ca));

	w->data->btree_level = c->root->level;

	bkey_copy(&w->data->btree_root, &c->root->key);
	bkey_copy(&w->data->uuid_bucket, &c->uuid_bucket);

	w->data->prio_bucket[ca->sb.nr_this_dev] = ca->prio_buckets[0];
	w->data->magic		= jset_magic(&ca->sb);
	w->data->version	= BCACHE_JSET_VERSION;
	w->data->last_seq	= last_seq(&c->journal);
	w->data->csum		= csum_set(w->data);

	for (i = 0; i < KEY_PTRS(k); i++) {
		ca = c->cache;
		bio = &ca->journal.bio;

		atomic_long_add(sectors, &ca->meta_sectors_written);

		bio_reset(bio, ca->bdev, REQ_OP_WRITE |
			  REQ_SYNC | REQ_META | REQ_PREFLUSH | REQ_FUA);
		bio->bi_iter.bi_sector	= PTR_OFFSET(k, i);
		bio->bi_iter.bi_size = sectors << 9;

		bio->bi_end_io	= journal_write_endio;
		bio->bi_private = w;
		bch_bio_map(bio, w->data);

		trace_bcache_journal_write(bio, w->data->keys);
		bio_list_add(&list, bio);

		SET_PTR_OFFSET(k, i, PTR_OFFSET(k, i) + sectors);

		ca->journal.seq[ca->journal.cur_idx] = w->data->seq;
	}

	/* If KEY_PTRS(k) == 0, this jset gets lost in air */
	BUG_ON(i == 0);

	atomic_dec_bug(&fifo_back(&c->journal.pin));
	bch_journal_next(&c->journal);
	journal_reclaim(c);

	spin_unlock(&c->journal.lock);

	while ((bio = bio_list_pop(&list)))
		closure_bio_submit(c, bio, cl);

	continue_at(cl, journal_write_done, NULL);
}

static CLOSURE_CALLBACK(journal_write)
{
	closure_type(c, struct cache_set, journal.io);

	spin_lock(&c->journal.lock);
	journal_write_unlocked(&cl->work);
}

static void journal_try_write(struct cache_set *c)
	__releases(c->journal.lock)
{
	struct closure *cl = &c->journal.io;
	struct journal_write *w = c->journal.cur;

	w->need_write = true;

	if (!c->journal.io_in_flight) {
		c->journal.io_in_flight = 1;
		closure_call(cl, journal_write_unlocked, NULL, &c->cl);
	} else {
		spin_unlock(&c->journal.lock);
	}
}

static struct journal_write *journal_wait_for_write(struct cache_set *c,
						    unsigned int nkeys)
	__acquires(&c->journal.lock)
{
	size_t sectors;
	struct closure cl;
	bool wait = false;
	struct cache *ca = c->cache;

	closure_init_stack(&cl);

	spin_lock(&c->journal.lock);

	while (1) {
		struct journal_write *w = c->journal.cur;

		sectors = __set_blocks(w->data, w->data->keys + nkeys,
				       block_bytes(ca)) * ca->sb.block_size;

		if (sectors <= min_t(size_t,
				     c->journal.blocks_free * ca->sb.block_size,
				     PAGE_SECTORS << JSET_BITS))
			return w;

		if (wait)
			closure_wait(&c->journal.wait, &cl);

		if (!journal_full(&c->journal)) {
			if (wait)
				trace_bcache_journal_entry_full(c);

			/*
			 * XXX: If we were inserting so many keys that they
			 * won't fit in an _empty_ journal write, we'll
			 * deadlock. For now, handle this in
			 * bch_keylist_realloc() - but something to think about.
			 */
			BUG_ON(!w->data->keys);

			journal_try_write(c); /* unlocks */
		} else {
			if (wait)
				trace_bcache_journal_full(c);

			journal_reclaim(c);
			spin_unlock(&c->journal.lock);

			btree_flush_write(c);
		}

		closure_sync(&cl);
		spin_lock(&c->journal.lock);
		wait = true;
	}
}

static void journal_write_work(struct work_struct *work)
{
	struct cache_set *c = container_of(to_delayed_work(work),
					   struct cache_set,
					   journal.work);
	spin_lock(&c->journal.lock);
	if (c->journal.cur->dirty)
		journal_try_write(c);
	else
		spin_unlock(&c->journal.lock);
}

/*
 * Entry point to the journalling code - bio_insert() and btree_invalidate()
 * pass bch_journal() a list of keys to be journalled, and then
 * bch_journal() hands those same keys off to btree_insert_async()
 */

atomic_t *bch_journal(struct cache_set *c,
		      struct keylist *keys,
		      struct closure *parent)
{
	struct journal_write *w;
	atomic_t *ret;

	/* No journaling if CACHE_SET_IO_DISABLE set already */
	if (unlikely(test_bit(CACHE_SET_IO_DISABLE, &c->flags)))
		return NULL;

	if (!CACHE_SYNC(&c->cache->sb))
		return NULL;

	w = journal_wait_for_write(c, bch_keylist_nkeys(keys));

	memcpy(bset_bkey_last(w->data), keys->keys, bch_keylist_bytes(keys));
	w->data->keys += bch_keylist_nkeys(keys);

	ret = &fifo_back(&c->journal.pin);
	atomic_inc(ret);

	if (parent) {
		closure_wait(&w->wait, parent);
		journal_try_write(c);
	} else if (!w->dirty) {
		w->dirty = true;
		queue_delayed_work(bch_flush_wq, &c->journal.work,
				   msecs_to_jiffies(c->journal_delay_ms));
		spin_unlock(&c->journal.lock);
	} else {
		spin_unlock(&c->journal.lock);
	}


	return ret;
}

void bch_journal_meta(struct cache_set *c, struct closure *cl)
{
	struct keylist keys;
	atomic_t *ref;

	bch_keylist_init(&keys);

	ref = bch_journal(c, &keys, cl);
	if (ref)
		atomic_dec_bug(ref);
}

void bch_journal_free(struct cache_set *c)
{
	free_pages((unsigned long) c->journal.w[1].data, JSET_BITS);
	free_pages((unsigned long) c->journal.w[0].data, JSET_BITS);
	free_fifo(&c->journal.pin);
}

int bch_journal_alloc(struct cache_set *c)
{
	struct journal *j = &c->journal;

	spin_lock_init(&j->lock);
	spin_lock_init(&j->flush_write_lock);
	INIT_DELAYED_WORK(&j->work, journal_write_work);

	c->journal_delay_ms = 100;

	j->w[0].c = c;
	j->w[1].c = c;

	if (!(init_fifo(&j->pin, JOURNAL_PIN, GFP_KERNEL)) ||
	    !(j->w[0].data = (void *) __get_free_pages(GFP_KERNEL|__GFP_COMP, JSET_BITS)) ||
	    !(j->w[1].data = (void *) __get_free_pages(GFP_KERNEL|__GFP_COMP, JSET_BITS)))
		return -ENOMEM;

	return 0;
}