path: root/fs/bcachefs/alloc_foreground.c

// SPDX-License-Identifier: GPL-2.0
/*
 * Copyright 2012 Google, Inc.
 *
 * Foreground allocator code: allocate buckets from freelist, and allocate in
 * sector granularity from writepoints.
 *
 * bch2_bucket_alloc() allocates a single bucket from a specific device.
 *
 * bch2_bucket_alloc_set() allocates one or more buckets from different devices
 * in a given filesystem.
 */

#include "bcachefs.h"
#include "alloc_background.h"
#include "alloc_foreground.h"
#include "backpointers.h"
#include "btree_iter.h"
#include "btree_update.h"
#include "btree_gc.h"
#include "buckets.h"
#include "buckets_waiting_for_journal.h"
#include "clock.h"
#include "debug.h"
#include "disk_groups.h"
#include "ec.h"
#include "error.h"
#include "io.h"
#include "journal.h"
#include "movinggc.h"
#include "nocow_locking.h"
#include "trace.h"

#include <linux/math64.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>

static void bch2_trans_mutex_lock_norelock(struct btree_trans *trans,
					   struct mutex *lock)
{
	if (!mutex_trylock(lock)) {
		bch2_trans_unlock(trans);
		mutex_lock(lock);
	}
}

const char * const bch2_watermarks[] = {
#define x(t) #t,
	BCH_WATERMARKS()
#undef x
	NULL
};

/*
 * Open buckets represent a bucket that's currently being allocated from.  They
 * serve two purposes:
 *
 *  - They track buckets that have been partially allocated, allowing for
 *    sub-bucket sized allocations - they're used by the sector allocator below
 *
 *  - They provide a reference to the buckets they own that mark and sweep GC
 *    can find, until the new allocation has a pointer to it inserted into the
 *    btree
 *
 * When allocating some space with the sector allocator, the allocation comes
 * with a reference to an open bucket - the caller is required to put that
 * reference _after_ doing the index update that makes its allocation reachable.
 */

void bch2_reset_alloc_cursors(struct bch_fs *c)
{
	struct bch_dev *ca;
	unsigned i;

	rcu_read_lock();
	for_each_member_device_rcu(ca, c, i, NULL)
		ca->alloc_cursor = 0;
	rcu_read_unlock();
}

static void bch2_open_bucket_hash_add(struct bch_fs *c, struct open_bucket *ob)
{
	open_bucket_idx_t idx = ob - c->open_buckets;
	open_bucket_idx_t *slot = open_bucket_hashslot(c, ob->dev, ob->bucket);

	ob->hash = *slot;
	*slot = idx;
}

static void bch2_open_bucket_hash_remove(struct bch_fs *c, struct open_bucket *ob)
{
	open_bucket_idx_t idx = ob - c->open_buckets;
	open_bucket_idx_t *slot = open_bucket_hashslot(c, ob->dev, ob->bucket);

	while (*slot != idx) {
		BUG_ON(!*slot);
		slot = &c->open_buckets[*slot].hash;
	}

	*slot = ob->hash;
	ob->hash = 0;
}

void __bch2_open_bucket_put(struct bch_fs *c, struct open_bucket *ob)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->dev);

	if (ob->ec) {
		ec_stripe_new_put(c, ob->ec, STRIPE_REF_io);
		return;
	}

	percpu_down_read(&c->mark_lock);
	spin_lock(&ob->lock);

	ob->valid = false;
	ob->data_type = 0;

	spin_unlock(&ob->lock);
	percpu_up_read(&c->mark_lock);

	spin_lock(&c->freelist_lock);
	bch2_open_bucket_hash_remove(c, ob);

	ob->freelist = c->open_buckets_freelist;
	c->open_buckets_freelist = ob - c->open_buckets;

	c->open_buckets_nr_free++;
	ca->nr_open_buckets--;
	spin_unlock(&c->freelist_lock);

	closure_wake_up(&c->open_buckets_wait);
}

void bch2_open_bucket_write_error(struct bch_fs *c,
				  struct open_buckets *obs,
				  unsigned dev)
{
	struct open_bucket *ob;
	unsigned i;

	open_bucket_for_each(c, obs, ob, i)
		if (ob->dev == dev && ob->ec)
			bch2_ec_bucket_cancel(c, ob);
}

static struct open_bucket *bch2_open_bucket_alloc(struct bch_fs *c)
{
	struct open_bucket *ob;

	BUG_ON(!c->open_buckets_freelist || !c->open_buckets_nr_free);

	ob = c->open_buckets + c->open_buckets_freelist;
	c->open_buckets_freelist = ob->freelist;
	atomic_set(&ob->pin, 1);
	ob->data_type = 0;

	c->open_buckets_nr_free--;
	return ob;
}

static void open_bucket_free_unused(struct bch_fs *c, struct open_bucket *ob)
{
	BUG_ON(c->open_buckets_partial_nr >=
	       ARRAY_SIZE(c->open_buckets_partial));

	spin_lock(&c->freelist_lock);
	ob->on_partial_list = true;
	c->open_buckets_partial[c->open_buckets_partial_nr++] =
		ob - c->open_buckets;
	spin_unlock(&c->freelist_lock);

	closure_wake_up(&c->open_buckets_wait);
	closure_wake_up(&c->freelist_wait);
}

/* _only_ for allocating the journal on a new device: */
long bch2_bucket_alloc_new_fs(struct bch_dev *ca)
{
	while (ca->new_fs_bucket_idx < ca->mi.nbuckets) {
		u64 b = ca->new_fs_bucket_idx++;

		if (!is_superblock_bucket(ca, b) &&
		    (!ca->buckets_nouse || !test_bit(b, ca->buckets_nouse)))
			return b;
	}

	return -1;
}

static inline unsigned open_buckets_reserved(enum bch_watermark watermark)
{
	switch (watermark) {
	case BCH_WATERMARK_reclaim:
		return 0;
	case BCH_WATERMARK_btree:
	case BCH_WATERMARK_btree_copygc:
		return OPEN_BUCKETS_COUNT / 4;
	case BCH_WATERMARK_copygc:
		return OPEN_BUCKETS_COUNT / 3;
	default:
		return OPEN_BUCKETS_COUNT / 2;
	}
}

static struct open_bucket *__try_alloc_bucket(struct bch_fs *c, struct bch_dev *ca,
					      u64 bucket,
					      enum bch_watermark watermark,
					      const struct bch_alloc_v4 *a,
					      struct bucket_alloc_state *s,
					      struct closure *cl)
{
	struct open_bucket *ob;

	if (unlikely(ca->buckets_nouse && test_bit(bucket, ca->buckets_nouse))) {
		s->skipped_nouse++;
		return NULL;
	}

	if (bch2_bucket_is_open(c, ca->dev_idx, bucket)) {
		s->skipped_open++;
		return NULL;
	}

	if (bch2_bucket_needs_journal_commit(&c->buckets_waiting_for_journal,
			c->journal.flushed_seq_ondisk, ca->dev_idx, bucket)) {
		s->skipped_need_journal_commit++;
		return NULL;
	}

	if (bch2_bucket_nocow_is_locked(&c->nocow_locks, POS(ca->dev_idx, bucket))) {
		s->skipped_nocow++;
		return NULL;
	}

	spin_lock(&c->freelist_lock);

	if (unlikely(c->open_buckets_nr_free <= open_buckets_reserved(watermark))) {
		if (cl)
			closure_wait(&c->open_buckets_wait, cl);

		if (!c->blocked_allocate_open_bucket)
			c->blocked_allocate_open_bucket = local_clock();

		spin_unlock(&c->freelist_lock);
		return ERR_PTR(-BCH_ERR_open_buckets_empty);
	}

	/* Recheck under lock: */
	if (bch2_bucket_is_open(c, ca->dev_idx, bucket)) {
		spin_unlock(&c->freelist_lock);
		s->skipped_open++;
		return NULL;
	}

	ob = bch2_open_bucket_alloc(c);

	spin_lock(&ob->lock);

	ob->valid	= true;
	ob->sectors_free = ca->mi.bucket_size;
	ob->dev		= ca->dev_idx;
	ob->gen		= a->gen;
	ob->bucket	= bucket;
	spin_unlock(&ob->lock);

	ca->nr_open_buckets++;
	bch2_open_bucket_hash_add(c, ob);

	if (c->blocked_allocate_open_bucket) {
		bch2_time_stats_update(
			&c->times[BCH_TIME_blocked_allocate_open_bucket],
			c->blocked_allocate_open_bucket);
		c->blocked_allocate_open_bucket = 0;
	}

	if (c->blocked_allocate) {
		bch2_time_stats_update(
			&c->times[BCH_TIME_blocked_allocate],
			c->blocked_allocate);
		c->blocked_allocate = 0;
	}

	spin_unlock(&c->freelist_lock);
	return ob;
}

static struct open_bucket *try_alloc_bucket(struct btree_trans *trans, struct bch_dev *ca,
					    enum bch_watermark watermark, u64 free_entry,
					    struct bucket_alloc_state *s,
					    struct bkey_s_c freespace_k,
					    struct closure *cl)
{
	struct bch_fs *c = trans->c;
	struct btree_iter iter = { NULL };
	struct bkey_s_c k;
	struct open_bucket *ob;
	struct bch_alloc_v4 a_convert;
	const struct bch_alloc_v4 *a;
	u64 b = free_entry & ~(~0ULL << 56);
	unsigned genbits = free_entry >> 56;
	struct printbuf buf = PRINTBUF;
	int ret;

	if (b < ca->mi.first_bucket || b >= ca->mi.nbuckets) {
		prt_printf(&buf, "freespace btree has bucket outside allowed range %u-%llu\n"
		       "  freespace key ",
			ca->mi.first_bucket, ca->mi.nbuckets);
		bch2_bkey_val_to_text(&buf, c, freespace_k);
		bch2_trans_inconsistent(trans, "%s", buf.buf);
		ob = ERR_PTR(-EIO);
		goto err;
	}

	k = bch2_bkey_get_iter(trans, &iter,
			       BTREE_ID_alloc, POS(ca->dev_idx, b),
			       BTREE_ITER_CACHED);
	ret = bkey_err(k);
	if (ret) {
		ob = ERR_PTR(ret);
		goto err;
	}

	a = bch2_alloc_to_v4(k, &a_convert);

	if (a->data_type != BCH_DATA_free) {
		if (!test_bit(BCH_FS_CHECK_ALLOC_DONE, &c->flags)) {
			ob = NULL;
			goto err;
		}

		prt_printf(&buf, "non free bucket in freespace btree\n"
		       "  freespace key ");
		bch2_bkey_val_to_text(&buf, c, freespace_k);
		prt_printf(&buf, "\n  ");
		bch2_bkey_val_to_text(&buf, c, k);
		bch2_trans_inconsistent(trans, "%s", buf.buf);
		ob = ERR_PTR(-EIO);
		goto err;
	}

	if (genbits != (alloc_freespace_genbits(*a) >> 56) &&
	    test_bit(BCH_FS_CHECK_ALLOC_DONE, &c->flags)) {
		prt_printf(&buf, "bucket in freespace btree with wrong genbits (got %u should be %llu)\n"
		       "  freespace key ",
		       genbits, alloc_freespace_genbits(*a) >> 56);
		bch2_bkey_val_to_text(&buf, c, freespace_k);
		prt_printf(&buf, "\n  ");
		bch2_bkey_val_to_text(&buf, c, k);
		bch2_trans_inconsistent(trans, "%s", buf.buf);
		ob = ERR_PTR(-EIO);
		goto err;

	}

	if (!test_bit(BCH_FS_CHECK_BACKPOINTERS_DONE, &c->flags)) {
		struct bch_backpointer bp;
		struct bpos bp_pos = POS_MIN;

		ret = bch2_get_next_backpointer(trans, POS(ca->dev_idx, b), -1,
						&bp_pos, &bp,
						BTREE_ITER_NOPRESERVE);
		if (ret) {
			ob = ERR_PTR(ret);
			goto err;
		}

		if (!bkey_eq(bp_pos, POS_MAX)) {
			/*
			 * Bucket may have data in it - we don't call
			 * bc2h_trans_inconnsistent() because fsck hasn't
			 * finished yet
			 */
			ob = NULL;
			goto err;
		}
	}

	ob = __try_alloc_bucket(c, ca, b, watermark, a, s, cl);
	if (!ob)
		iter.path->preserve = false;
err:
	if (iter.trans && iter.path)
		set_btree_iter_dontneed(&iter);
	bch2_trans_iter_exit(trans, &iter);
	printbuf_exit(&buf);
	return ob;
}

/*
 * This path is for before the freespace btree is initialized:
 *
 * If ca->new_fs_bucket_idx is nonzero, we haven't yet marked superblock &
 * journal buckets - journal buckets will be < ca->new_fs_bucket_idx
 */
static noinline struct open_bucket *
bch2_bucket_alloc_early(struct btree_trans *trans,
			struct bch_dev *ca,
			enum bch_watermark watermark,
			struct bucket_alloc_state *s,
			struct closure *cl)
{
	struct btree_iter iter;
	struct bkey_s_c k;
	struct open_bucket *ob = NULL;
	u64 alloc_start = max_t(u64, ca->mi.first_bucket, ca->new_fs_bucket_idx);
	u64 alloc_cursor = max(alloc_start, READ_ONCE(ca->alloc_cursor));
	int ret;
again:
	for_each_btree_key_norestart(trans, iter, BTREE_ID_alloc, POS(ca->dev_idx, alloc_cursor),
			   BTREE_ITER_SLOTS, k, ret) {
		struct bch_alloc_v4 a_convert;
		const struct bch_alloc_v4 *a;

		if (bkey_ge(k.k->p, POS(ca->dev_idx, ca->mi.nbuckets)))
			break;

		if (ca->new_fs_bucket_idx &&
		    is_superblock_bucket(ca, k.k->p.offset))
			continue;

		a = bch2_alloc_to_v4(k, &a_convert);

		if (a->data_type != BCH_DATA_free)
			continue;

		s->buckets_seen++;

		ob = __try_alloc_bucket(trans->c, ca, k.k->p.offset, watermark, a, s, cl);
		if (ob)
			break;
	}
	bch2_trans_iter_exit(trans, &iter);

	ca->alloc_cursor = alloc_cursor;

	if (!ob && ret)
		ob = ERR_PTR(ret);

	if (!ob && alloc_cursor > alloc_start) {
		alloc_cursor = alloc_start;
		goto again;
	}

	return ob;
}

static struct open_bucket *bch2_bucket_alloc_freelist(struct btree_trans *trans,
						   struct bch_dev *ca,
						   enum bch_watermark watermark,
						   struct bucket_alloc_state *s,
						   struct closure *cl)
{
	struct btree_iter iter;
	struct bkey_s_c k;
	struct open_bucket *ob = NULL;
	u64 alloc_start = max_t(u64, ca->mi.first_bucket, READ_ONCE(ca->alloc_cursor));
	u64 alloc_cursor = alloc_start;
	int ret;

	BUG_ON(ca->new_fs_bucket_idx);
again:
	for_each_btree_key_norestart(trans, iter, BTREE_ID_freespace,
				     POS(ca->dev_idx, alloc_cursor), 0, k, ret) {
		if (k.k->p.inode != ca->dev_idx)
			break;

		for (alloc_cursor = max(alloc_cursor, bkey_start_offset(k.k));
		     alloc_cursor < k.k->p.offset;
		     alloc_cursor++) {
			ret = btree_trans_too_many_iters(trans);
			if (ret) {
				ob = ERR_PTR(ret);
				break;
			}

			s->buckets_seen++;

			ob = try_alloc_bucket(trans, ca, watermark,
					      alloc_cursor, s, k, cl);
			if (ob) {
				iter.path->preserve = false;
				break;
			}
		}

		if (ob || ret)
			break;
	}
	bch2_trans_iter_exit(trans, &iter);

	ca->alloc_cursor = alloc_cursor;

	if (!ob && ret)
		ob = ERR_PTR(ret);

	if (!ob && alloc_start > ca->mi.first_bucket) {
		alloc_cursor = alloc_start = ca->mi.first_bucket;
		goto again;
	}

	return ob;
}

/**
 * bch_bucket_alloc - allocate a single bucket from a specific device
 *
 * Returns index of bucket on success, 0 on failure
 */
static struct open_bucket *bch2_bucket_alloc_trans(struct btree_trans *trans,
				      struct bch_dev *ca,
				      enum bch_watermark watermark,
				      struct closure *cl,
				      struct bch_dev_usage *usage)
{
	struct bch_fs *c = trans->c;
	struct open_bucket *ob = NULL;
	bool freespace = READ_ONCE(ca->mi.freespace_initialized);
	u64 avail;
	struct bucket_alloc_state s = { 0 };
	bool waiting = false;
again:
	bch2_dev_usage_read_fast(ca, usage);
	avail = dev_buckets_free(ca, *usage, watermark);

	if (usage->d[BCH_DATA_need_discard].buckets > avail)
		bch2_do_discards(c);

	if (usage->d[BCH_DATA_need_gc_gens].buckets > avail)
		bch2_do_gc_gens(c);

	if (should_invalidate_buckets(ca, *usage))
		bch2_do_invalidates(c);

	if (!avail) {
		if (cl && !waiting) {
			closure_wait(&c->freelist_wait, cl);
			waiting = true;
			goto again;
		}

		if (!c->blocked_allocate)
			c->blocked_allocate = local_clock();

		ob = ERR_PTR(-BCH_ERR_freelist_empty);
		goto err;
	}

	if (waiting)
		closure_wake_up(&c->freelist_wait);
alloc:
	ob = likely(freespace)
		? bch2_bucket_alloc_freelist(trans, ca, watermark, &s, cl)
		: bch2_bucket_alloc_early(trans, ca, watermark, &s, cl);

	if (s.skipped_need_journal_commit * 2 > avail)
		bch2_journal_flush_async(&c->journal, NULL);

	if (!ob && freespace && !test_bit(BCH_FS_CHECK_ALLOC_DONE, &c->flags)) {
		freespace = false;
		goto alloc;
	}
err:
	if (!ob)
		ob = ERR_PTR(-BCH_ERR_no_buckets_found);

	if (!IS_ERR(ob))
		trace_and_count(c, bucket_alloc, ca,
				bch2_watermarks[watermark],
				ob->bucket,
				usage->d[BCH_DATA_free].buckets,
				avail,
				bch2_copygc_wait_amount(c),
				c->copygc_wait - atomic64_read(&c->io_clock[WRITE].now),
				&s,
				cl == NULL,
				"");
	else if (!bch2_err_matches(PTR_ERR(ob), BCH_ERR_transaction_restart))
		trace_and_count(c, bucket_alloc_fail, ca,
				bch2_watermarks[watermark],
				0,
				usage->d[BCH_DATA_free].buckets,
				avail,
				bch2_copygc_wait_amount(c),
				c->copygc_wait - atomic64_read(&c->io_clock[WRITE].now),
				&s,
				cl == NULL,
				bch2_err_str(PTR_ERR(ob)));

	return ob;
}

struct open_bucket *bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
				      enum bch_watermark watermark,
				      struct closure *cl)
{
	struct bch_dev_usage usage;
	struct open_bucket *ob;

	bch2_trans_do(c, NULL, NULL, 0,
		      PTR_ERR_OR_ZERO(ob = bch2_bucket_alloc_trans(&trans, ca, watermark,
							cl, &usage)));
	return ob;
}

static int __dev_stripe_cmp(struct dev_stripe_state *stripe,
			    unsigned l, unsigned r)
{
	return ((stripe->next_alloc[l] > stripe->next_alloc[r]) -
		(stripe->next_alloc[l] < stripe->next_alloc[r]));
}

#define dev_stripe_cmp(l, r) __dev_stripe_cmp(stripe, l, r)

struct dev_alloc_list bch2_dev_alloc_list(struct bch_fs *c,
					  struct dev_stripe_state *stripe,
					  struct bch_devs_mask *devs)
{
	struct dev_alloc_list ret = { .nr = 0 };
	unsigned i;

	for_each_set_bit(i, devs->d, BCH_SB_MEMBERS_MAX)
		ret.devs[ret.nr++] = i;

	bubble_sort(ret.devs, ret.nr, dev_stripe_cmp);
	return ret;
}

static inline void bch2_dev_stripe_increment_inlined(struct bch_dev *ca,
			       struct dev_stripe_state *stripe,
			       struct bch_dev_usage *usage)
{
	u64 *v = stripe->next_alloc + ca->dev_idx;
	u64 free_space = dev_buckets_available(ca, BCH_WATERMARK_normal);
	u64 free_space_inv = free_space
		? div64_u64(1ULL << 48, free_space)
		: 1ULL << 48;
	u64 scale = *v / 4;

	if (*v + free_space_inv >= *v)
		*v += free_space_inv;
	else
		*v = U64_MAX;

	for (v = stripe->next_alloc;
	     v < stripe->next_alloc + ARRAY_SIZE(stripe->next_alloc); v++)
		*v = *v < scale ? 0 : *v - scale;
}

void bch2_dev_stripe_increment(struct bch_dev *ca,
			       struct dev_stripe_state *stripe)
{
	struct bch_dev_usage usage;

	bch2_dev_usage_read_fast(ca, &usage);
	bch2_dev_stripe_increment_inlined(ca, stripe, &usage);
}

static int add_new_bucket(struct bch_fs *c,
			   struct open_buckets *ptrs,
			   struct bch_devs_mask *devs_may_alloc,
			   unsigned nr_replicas,
			   unsigned *nr_effective,
			   bool *have_cache,
			   unsigned flags,
			   struct open_bucket *ob)
{
	unsigned durability =
		bch_dev_bkey_exists(c, ob->dev)->mi.durability;

	BUG_ON(*nr_effective >= nr_replicas);
	BUG_ON(flags & BCH_WRITE_ONLY_SPECIFIED_DEVS);

	__clear_bit(ob->dev, devs_may_alloc->d);
	*nr_effective	+= (flags & BCH_WRITE_ONLY_SPECIFIED_DEVS)
		? durability : 1;
	*have_cache	|= !durability;

	ob_push(c, ptrs, ob);

	if (*nr_effective >= nr_replicas)
		return 1;
	if (ob->ec)
		return 1;
	return 0;
}

int bch2_bucket_alloc_set_trans(struct btree_trans *trans,
		      struct open_buckets *ptrs,
		      struct dev_stripe_state *stripe,
		      struct bch_devs_mask *devs_may_alloc,
		      unsigned nr_replicas,
		      unsigned *nr_effective,
		      bool *have_cache,
		      unsigned flags,
		      enum bch_data_type data_type,
		      enum bch_watermark watermark,
		      struct closure *cl)
{
	struct bch_fs *c = trans->c;
	struct dev_alloc_list devs_sorted =
		bch2_dev_alloc_list(c, stripe, devs_may_alloc);
	unsigned dev;
	struct bch_dev *ca;
	int ret = -BCH_ERR_insufficient_devices;
	unsigned i;

	BUG_ON(*nr_effective >= nr_replicas);

	for (i = 0; i < devs_sorted.nr; i++) {
		struct bch_dev_usage usage;
		struct open_bucket *ob;

		dev = devs_sorted.devs[i];

		rcu_read_lock();
		ca = rcu_dereference(c->devs[dev]);
		if (ca)
			percpu_ref_get(&ca->ref);
		rcu_read_unlock();

		if (!ca)
			continue;

		if (!ca->mi.durability && *have_cache) {
			percpu_ref_put(&ca->ref);
			continue;
		}

		ob = bch2_bucket_alloc_trans(trans, ca, watermark, cl, &usage);
		if (!IS_ERR(ob))
			bch2_dev_stripe_increment_inlined(ca, stripe, &usage);
		percpu_ref_put(&ca->ref);

		if (IS_ERR(ob)) {
			ret = PTR_ERR(ob);
			if (bch2_err_matches(ret, BCH_ERR_transaction_restart) || cl)
				break;
			continue;
		}

		ob->data_type = data_type;

		if (add_new_bucket(c, ptrs, devs_may_alloc,
				   nr_replicas, nr_effective,
				   have_cache, flags, ob)) {
			ret = 0;
			break;
		}
	}

	return ret;
}

/* Allocate from stripes: */

/*
 * if we can't allocate a new stripe because there are already too many
 * partially filled stripes, force allocating from an existing stripe even when
 * it's to a device we don't want:
 */

static int bucket_alloc_from_stripe(struct btree_trans *trans,
			 struct open_buckets *ptrs,
			 struct write_point *wp,
			 struct bch_devs_mask *devs_may_alloc,
			 u16 target,
			 unsigned nr_replicas,
			 unsigned *nr_effective,
			 bool *have_cache,
			 enum bch_watermark watermark,
			 unsigned flags,
			 struct closure *cl)
{
	struct bch_fs *c = trans->c;
	struct dev_alloc_list devs_sorted;
	struct ec_stripe_head *h;
	struct open_bucket *ob;
	struct bch_dev *ca;
	unsigned i, ec_idx;
	int ret = 0;

	if (nr_replicas < 2)
		return 0;

	if (ec_open_bucket(c, ptrs))
		return 0;

	h = bch2_ec_stripe_head_get(trans, target, 0, nr_replicas - 1, watermark, cl);
	if (IS_ERR(h))
		return PTR_ERR(h);
	if (!h)
		return 0;

	devs_sorted = bch2_dev_alloc_list(c, &wp->stripe, devs_may_alloc);

	for (i = 0; i < devs_sorted.nr; i++)
		for (ec_idx = 0; ec_idx < h->s->nr_data; ec_idx++) {
			if (!h->s->blocks[ec_idx])
				continue;

			ob = c->open_buckets + h->s->blocks[ec_idx];
			if (ob->dev == devs_sorted.devs[i] &&
			    !test_and_set_bit(ec_idx, h->s->blocks_allocated))
				goto got_bucket;
		}
	goto out_put_head;
got_bucket:
	ca = bch_dev_bkey_exists(c, ob->dev);

	ob->ec_idx	= ec_idx;
	ob->ec		= h->s;
	ec_stripe_new_get(h->s, STRIPE_REF_io);

	ret = add_new_bucket(c, ptrs, devs_may_alloc,
			     nr_replicas, nr_effective,
			     have_cache, flags, ob);
out_put_head:
	bch2_ec_stripe_head_put(c, h);
	return ret;
}

/* Sector allocator */

static bool want_bucket(struct bch_fs *c,
			struct write_point *wp,
			struct bch_devs_mask *devs_may_alloc,
			bool *have_cache, bool ec,
			struct open_bucket *ob)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->dev);

	if (!test_bit(ob->dev, devs_may_alloc->d))
		return false;

	if (ob->data_type != wp->data_type)
		return false;

	if (!ca->mi.durability &&
	    (wp->data_type == BCH_DATA_btree || ec || *have_cache))
		return false;

	if (ec != (ob->ec != NULL))
		return false;

	return true;
}

static int bucket_alloc_set_writepoint(struct bch_fs *c,
				       struct open_buckets *ptrs,
				       struct write_point *wp,
				       struct bch_devs_mask *devs_may_alloc,
				       unsigned nr_replicas,
				       unsigned *nr_effective,
				       bool *have_cache,
				       bool ec, unsigned flags)
{
	struct open_buckets ptrs_skip = { .nr = 0 };
	struct open_bucket *ob;
	unsigned i;
	int ret = 0;

	open_bucket_for_each(c, &wp->ptrs, ob, i) {
		if (!ret && want_bucket(c, wp, devs_may_alloc,
					have_cache, ec, ob))
			ret = add_new_bucket(c, ptrs, devs_may_alloc,
				       nr_replicas, nr_effective,
				       have_cache, flags, ob);
		else
			ob_push(c, &ptrs_skip, ob);
	}
	wp->ptrs = ptrs_skip;

	return ret;
}

static int bucket_alloc_set_partial(struct bch_fs *c,
				    struct open_buckets *ptrs,
				    struct write_point *wp,
				    struct bch_devs_mask *devs_may_alloc,
				    unsigned nr_replicas,
				    unsigned *nr_effective,
				    bool *have_cache, bool ec,
				    enum bch_watermark watermark,
				    unsigned flags)
{
	int i, ret = 0;

	if (!c->open_buckets_partial_nr)
		return 0;

	spin_lock(&c->freelist_lock);

	if (!c->open_buckets_partial_nr)
		goto unlock;

	for (i = c->open_buckets_partial_nr - 1; i >= 0; --i) {
		struct open_bucket *ob = c->open_buckets + c->open_buckets_partial[i];

		if (want_bucket(c, wp, devs_may_alloc, have_cache, ec, ob)) {
			struct bch_dev *ca = bch_dev_bkey_exists(c, ob->dev);
			struct bch_dev_usage usage;
			u64 avail;

			bch2_dev_usage_read_fast(ca, &usage);
			avail = dev_buckets_free(ca, usage, watermark);
			if (!avail)
				continue;

			array_remove_item(c->open_buckets_partial,
					  c->open_buckets_partial_nr,
					  i);
			ob->on_partial_list = false;

			ret = add_new_bucket(c, ptrs, devs_may_alloc,
					     nr_replicas, nr_effective,
					     have_cache, flags, ob);
			if (ret)
				break;
		}
	}
unlock:
	spin_unlock(&c->freelist_lock);
	return ret;
}

static int __open_bucket_add_buckets(struct btree_trans *trans,
			struct open_buckets *ptrs,
			struct write_point *wp,
			struct bch_devs_list *devs_have,
			u16 target,
			bool erasure_code,
			unsigned nr_replicas,
			unsigned *nr_effective,
			bool *have_cache,
			enum bch_watermark watermark,
			unsigned flags,
			struct closure *_cl)
{
	struct bch_fs *c = trans->c;
	struct bch_devs_mask devs;
	struct open_bucket *ob;
	struct closure *cl = NULL;
	unsigned i;
	int ret;

	devs = target_rw_devs(c, wp->data_type, target);

	/* Don't allocate from devices we already have pointers to: */
	for (i = 0; i < devs_have->nr; i++)
		__clear_bit(devs_have->devs[i], devs.d);

	open_bucket_for_each(c, ptrs, ob, i)
		__clear_bit(ob->dev, devs.d);

	if (erasure_code && ec_open_bucket(c, ptrs))
		return 0;

	ret = bucket_alloc_set_writepoint(c, ptrs, wp, &devs,
				 nr_replicas, nr_effective,
				 have_cache, erasure_code, flags);
	if (ret)
		return ret;

	ret = bucket_alloc_set_partial(c, ptrs, wp, &devs,
				 nr_replicas, nr_effective,
				 have_cache, erasure_code, watermark, flags);
	if (ret)
		return ret;

	if (erasure_code) {
		ret = bucket_alloc_from_stripe(trans, ptrs, wp, &devs,
					 target,
					 nr_replicas, nr_effective,
					 have_cache,
					 watermark, flags, _cl);
	} else {
retry_blocking:
		/*
		 * Try nonblocking first, so that if one device is full we'll try from
		 * other devices:
		 */
		ret = bch2_bucket_alloc_set_trans(trans, ptrs, &wp->stripe, &devs,
					nr_replicas, nr_effective, have_cache,
					flags, wp->data_type, watermark, cl);
		if (ret &&
		    !bch2_err_matches(ret, BCH_ERR_transaction_restart) &&
		    !bch2_err_matches(ret, BCH_ERR_insufficient_devices) &&
		    !cl && _cl) {
			cl = _cl;
			goto retry_blocking;
		}

	}

	return ret;
}

static int open_bucket_add_buckets(struct btree_trans *trans,
			struct open_buckets *ptrs,
			struct write_point *wp,
			struct bch_devs_list *devs_have,
			u16 target,
			unsigned erasure_code,
			unsigned nr_replicas,
			unsigned *nr_effective,
			bool *have_cache,
			enum bch_watermark watermark,
			unsigned flags,
			struct closure *cl)
{
	int ret;

	if (erasure_code) {
		ret = __open_bucket_add_buckets(trans, ptrs, wp,
				devs_have, target, erasure_code,
				nr_replicas, nr_effective, have_cache,
				watermark, flags, cl);
		if (bch2_err_matches(ret, BCH_ERR_transaction_restart) ||
		    bch2_err_matches(ret, BCH_ERR_operation_blocked) ||
		    bch2_err_matches(ret, BCH_ERR_freelist_empty) ||
		    bch2_err_matches(ret, BCH_ERR_open_buckets_empty))
			return ret;
		if (*nr_effective >= nr_replicas)
			return 0;
	}

	ret = __open_bucket_add_buckets(trans, ptrs, wp,
			devs_have, target, false,
			nr_replicas, nr_effective, have_cache,
			watermark, flags, cl);
	return ret < 0 ? ret : 0;
}

static bool should_drop_bucket(struct open_bucket *ob, struct bch_fs *c,
			       struct bch_dev *ca, bool ec)
{
	if (ec) {
		return ob->ec != NULL;
	} else if (ca) {
		bool drop = ob->dev == ca->dev_idx;
		struct open_bucket *ob2;
		unsigned i;

		if (!drop && ob->ec) {
			mutex_lock(&ob->ec->lock);
			for (i = 0; i < ob->ec->new_stripe.key.v.nr_blocks; i++) {
				if (!ob->ec->blocks[i])
					continue;

				ob2 = c->open_buckets + ob->ec->blocks[i];
				drop |= ob2->dev == ca->dev_idx;
			}
			mutex_unlock(&ob->ec->lock);
		}

		return drop;
	} else {
		return true;
	}
}

static void bch2_writepoint_stop(struct bch_fs *c, struct bch_dev *ca,
				 bool ec, struct write_point *wp)
{
	struct open_buckets ptrs = { .nr = 0 };
	struct open_bucket *ob;
	unsigned i;

	mutex_lock(&wp->lock);
	open_bucket_for_each(c, &wp->ptrs, ob, i)
		if (should_drop_bucket(ob, c, ca, ec))
			bch2_open_bucket_put(c, ob);
		else
			ob_push(c, &ptrs, ob);
	wp->ptrs = ptrs;
	mutex_unlock(&wp->lock);
}

void bch2_open_buckets_stop(struct bch_fs *c, struct bch_dev *ca,
			    bool ec)
{
	unsigned i;

	/* Next, close write points that point to this device... */
	for (i = 0; i < ARRAY_SIZE(c->write_points); i++)
		bch2_writepoint_stop(c, ca, ec, &c->write_points[i]);

	bch2_writepoint_stop(c, ca, ec, &c->copygc_write_point);
	bch2_writepoint_stop(c, ca, ec, &c->rebalance_write_point);
	bch2_writepoint_stop(c, ca, ec, &c->btree_write_point);

	mutex_lock(&c->btree_reserve_cache_lock);
	while (c->btree_reserve_cache_nr) {
		struct btree_alloc *a =
			&c->btree_reserve_cache[--c->btree_reserve_cache_nr];

		bch2_open_buckets_put(c, &a->ob);
	}
	mutex_unlock(&c->btree_reserve_cache_lock);

	spin_lock(&c->freelist_lock);
	i = 0;
	while (i < c->open_buckets_partial_nr) {
		struct open_bucket *ob =
			c->open_buckets + c->open_buckets_partial[i];

		if (should_drop_bucket(ob, c, ca, ec)) {
			--c->open_buckets_partial_nr;
			swap(c->open_buckets_partial[i],
			     c->open_buckets_partial[c->open_buckets_partial_nr]);
			ob->on_partial_list = false;
			spin_unlock(&c->freelist_lock);
			bch2_open_bucket_put(c, ob);
			spin_lock(&c->freelist_lock);
		} else {
			i++;
		}
	}
	spin_unlock(&c->freelist_lock);

	bch2_ec_stop_dev(c, ca);
}

static inline struct hlist_head *writepoint_hash(struct bch_fs *c,
						 unsigned long write_point)
{
	unsigned hash =
		hash_long(write_point, ilog2(ARRAY_SIZE(c->write_points_hash)));

	return &c->write_points_hash[hash];
}

static struct write_point *__writepoint_find(struct hlist_head *head,
					     unsigned long write_point)
{
	struct write_point *wp;

	rcu_read_lock();
	hlist_for_each_entry_rcu(wp, head, node)
		if (wp->write_point == write_point)
			goto out;
	wp = NULL;
out:
	rcu_read_unlock();
	return wp;
}

static inline bool too_many_writepoints(struct bch_fs *c, unsigned factor)
{
	u64 stranded	= c->write_points_nr * c->bucket_size_max;
	u64 free	= bch2_fs_usage_read_short(c).free;

	return stranded * factor > free;
}

static bool try_increase_writepoints(struct bch_fs *c)
{
	struct write_point *wp;

	if (c->write_points_nr == ARRAY_SIZE(c->write_points) ||
	    too_many_writepoints(c, 32))
		return false;

	wp = c->write_points + c->write_points_nr++;
	hlist_add_head_rcu(&wp->node, writepoint_hash(c, wp->write_point));
	return true;
}

static bool try_decrease_writepoints(struct btree_trans *trans, unsigned old_nr)
{
	struct bch_fs *c = trans->c;
	struct write_point *wp;
	struct open_bucket *ob;
	unsigned i;

	mutex_lock(&c->write_points_hash_lock);
	if (c->write_points_nr < old_nr) {
		mutex_unlock(&c->write_points_hash_lock);
		return true;
	}

	if (c->write_points_nr == 1 ||
	    !too_many_writepoints(c, 8)) {
		mutex_unlock(&c->write_points_hash_lock);
		return false;
	}

	wp = c->write_points + --c->write_points_nr;

	hlist_del_rcu(&wp->node);
	mutex_unlock(&c->write_points_hash_lock);

	bch2_trans_mutex_lock_norelock(trans, &wp->lock);
	open_bucket_for_each(c, &wp->ptrs, ob, i)
		open_bucket_free_unused(c, ob);
	mutex_unlock(&wp->lock);
	return true;
}

static struct write_point *writepoint_find(struct btree_trans *trans,
					   unsigned long write_point)
{
	struct bch_fs *c = trans->c;
	struct write_point *wp, *oldest;
	struct hlist_head *head;

	if (!(write_point & 1UL)) {
		wp = (struct write_point *) write_point;
		bch2_trans_mutex_lock_norelock(trans, &wp->lock);
		return wp;
	}

	head = writepoint_hash(c, write_point);
restart_find:
	wp = __writepoint_find(head, write_point);
	if (wp) {
lock_wp:
		bch2_trans_mutex_lock_norelock(trans, &wp->lock);
		if (wp->write_point == write_point)
			goto out;
		mutex_unlock(&wp->lock);
		goto restart_find;
	}
restart_find_oldest:
	oldest = NULL;
	for (wp = c->write_points;
	     wp < c->write_points + c->write_points_nr; wp++)
		if (!oldest || time_before64(wp->last_used, oldest->last_used))
			oldest = wp;

	bch2_trans_mutex_lock_norelock(trans, &oldest->lock);
	bch2_trans_mutex_lock_norelock(trans, &c->write_points_hash_lock);
	if (oldest >= c->write_points + c->write_points_nr ||
	    try_increase_writepoints(c)) {
		mutex_unlock(&c->write_points_hash_lock);
		mutex_unlock(&oldest->lock);
		goto restart_find_oldest;
	}

	wp = __writepoint_find(head, write_point);
	if (wp && wp != oldest) {
		mutex_unlock(&c->write_points_hash_lock);
		mutex_unlock(&oldest->lock);
		goto lock_wp;
	}

	wp = oldest;
	hlist_del_rcu(&wp->node);
	wp->write_point = write_point;
	hlist_add_head_rcu(&wp->node, head);
	mutex_unlock(&c->write_points_hash_lock);
out:
	wp->last_used = local_clock();
	return wp;
}

/*
 * Get us an open_bucket we can allocate from, return with it locked:
 */
int bch2_alloc_sectors_start_trans(struct btree_trans *trans,
			     unsigned target,
			     unsigned erasure_code,
			     struct write_point_specifier write_point,
			     struct bch_devs_list *devs_have,
			     unsigned nr_replicas,
			     unsigned nr_replicas_required,
			     enum bch_watermark watermark,
			     unsigned flags,
			     struct closure *cl,
			     struct write_point **wp_ret)
{
	struct bch_fs *c = trans->c;
	struct write_point *wp;
	struct open_bucket *ob;
	struct open_buckets ptrs;
	unsigned nr_effective, write_points_nr;
	bool have_cache;
	int ret;
	int i;

	BUG_ON(flags & BCH_WRITE_ONLY_SPECIFIED_DEVS);

	BUG_ON(!nr_replicas || !nr_replicas_required);
retry:
	ptrs.nr		= 0;
	nr_effective	= 0;
	write_points_nr = c->write_points_nr;
	have_cache	= false;

	*wp_ret = wp = writepoint_find(trans, write_point.v);

	/* metadata may not allocate on cache devices: */
	if (wp->data_type != BCH_DATA_user)
		have_cache = true;

	if (target && !(flags & BCH_WRITE_ONLY_SPECIFIED_DEVS)) {
		ret = open_bucket_add_buckets(trans, &ptrs, wp, devs_have,
					      target, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, watermark,
					      flags, NULL);
		if (!ret ||
		    bch2_err_matches(ret, BCH_ERR_transaction_restart))
			goto alloc_done;

		/* Don't retry from all devices if we're out of open buckets: */
		if (bch2_err_matches(ret, BCH_ERR_open_buckets_empty))
			goto allocate_blocking;

		/*
		 * Only try to allocate cache (durability = 0 devices) from the
		 * specified target:
		 */
		have_cache = true;

		ret = open_bucket_add_buckets(trans, &ptrs, wp, devs_have,
					      0, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, watermark,
					      flags, cl);
	} else {
allocate_blocking:
		ret = open_bucket_add_buckets(trans, &ptrs, wp, devs_have,
					      target, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, watermark,
					      flags, cl);
	}
alloc_done:
	BUG_ON(!ret && nr_effective < nr_replicas);

	if (erasure_code && !ec_open_bucket(c, &ptrs))
		pr_debug("failed to get ec bucket: ret %u", ret);

	if (ret == -BCH_ERR_insufficient_devices &&
	    nr_effective >= nr_replicas_required)
		ret = 0;

	if (ret)
		goto err;

	/* Free buckets we didn't use: */
	open_bucket_for_each(c, &wp->ptrs, ob, i)
		open_bucket_free_unused(c, ob);

	wp->ptrs = ptrs;

	wp->sectors_free = UINT_MAX;

	open_bucket_for_each(c, &wp->ptrs, ob, i)
		wp->sectors_free = min(wp->sectors_free, ob->sectors_free);

	BUG_ON(!wp->sectors_free || wp->sectors_free == UINT_MAX);

	return 0;
err:
	open_bucket_for_each(c, &wp->ptrs, ob, i)
		if (ptrs.nr < ARRAY_SIZE(ptrs.v))
			ob_push(c, &ptrs, ob);
		else
			open_bucket_free_unused(c, ob);
	wp->ptrs = ptrs;

	mutex_unlock(&wp->lock);

	if (bch2_err_matches(ret, BCH_ERR_freelist_empty) &&
	    try_decrease_writepoints(trans, write_points_nr))
		goto retry;

	if (bch2_err_matches(ret, BCH_ERR_open_buckets_empty) ||
	    bch2_err_matches(ret, BCH_ERR_freelist_empty))
		return cl
			? -BCH_ERR_bucket_alloc_blocked
			: -BCH_ERR_ENOSPC_bucket_alloc;

	return ret;
}

struct bch_extent_ptr bch2_ob_ptr(struct bch_fs *c, struct open_bucket *ob)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->dev);

	return (struct bch_extent_ptr) {
		.type	= 1 << BCH_EXTENT_ENTRY_ptr,
		.gen	= ob->gen,
		.dev	= ob->dev,
		.offset	= bucket_to_sector(ca, ob->bucket) +
			ca->mi.bucket_size -
			ob->sectors_free,
	};
}

void bch2_alloc_sectors_append_ptrs(struct bch_fs *c, struct write_point *wp,
				    struct bkey_i *k, unsigned sectors,
				    bool cached)
{
	bch2_alloc_sectors_append_ptrs_inlined(c, wp, k, sectors, cached);
}

/*
 * Append pointers to the space we just allocated to @k, and mark @sectors space
 * as allocated out of @ob
 */
void bch2_alloc_sectors_done(struct bch_fs *c, struct write_point *wp)
{
	bch2_alloc_sectors_done_inlined(c, wp);
}

static inline void writepoint_init(struct write_point *wp,
				   enum bch_data_type type)
{
	mutex_init(&wp->lock);
	wp->data_type = type;

	INIT_WORK(&wp->index_update_work, bch2_write_point_do_index_updates);
	INIT_LIST_HEAD(&wp->writes);
	spin_lock_init(&wp->writes_lock);
}

void bch2_fs_allocator_foreground_init(struct bch_fs *c)
{
	struct open_bucket *ob;
	struct write_point *wp;

	mutex_init(&c->write_points_hash_lock);
	c->write_points_nr = ARRAY_SIZE(c->write_points);

	/* open bucket 0 is a sentinal NULL: */
	spin_lock_init(&c->open_buckets[0].lock);

	for (ob = c->open_buckets + 1;
	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets); ob++) {
		spin_lock_init(&ob->lock);
		c->open_buckets_nr_free++;

		ob->freelist = c->open_buckets_freelist;
		c->open_buckets_freelist = ob - c->open_buckets;
	}

	writepoint_init(&c->btree_write_point,		BCH_DATA_btree);
	writepoint_init(&c->rebalance_write_point,	BCH_DATA_user);
	writepoint_init(&c->copygc_write_point,		BCH_DATA_user);

	for (wp = c->write_points;
	     wp < c->write_points + c->write_points_nr; wp++) {
		writepoint_init(wp, BCH_DATA_user);

		wp->last_used	= local_clock();
		wp->write_point	= (unsigned long) wp;
		hlist_add_head_rcu(&wp->node,
				   writepoint_hash(c, wp->write_point));
	}
}

static void bch2_open_bucket_to_text(struct printbuf *out, struct bch_fs *c, struct open_bucket *ob)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->dev);
	unsigned data_type = ob->data_type;
	barrier(); /* READ_ONCE() doesn't work on bitfields */

	prt_printf(out, "%zu ref %u %s %u:%llu gen %u allocated %u/%u",
		   ob - c->open_buckets,
		   atomic_read(&ob->pin),
		   data_type < BCH_DATA_NR ? bch2_data_types[data_type] : "invalid data type",
		   ob->dev, ob->bucket, ob->gen,
		   ca->mi.bucket_size - ob->sectors_free, ca->mi.bucket_size);
	if (ob->ec)
		prt_printf(out, " ec idx %llu", ob->ec->idx);
	if (ob->on_partial_list)
		prt_str(out, " partial");
	prt_newline(out);
}

void bch2_open_buckets_to_text(struct printbuf *out, struct bch_fs *c)
{
	struct open_bucket *ob;

	out->atomic++;

	for (ob = c->open_buckets;
	     ob < c->open_buckets + ARRAY_SIZE(c->open_buckets);
	     ob++) {
		spin_lock(&ob->lock);
		if (ob->valid && !ob->on_partial_list)
			bch2_open_bucket_to_text(out, c, ob);
		spin_unlock(&ob->lock);
	}

	--out->atomic;
}

void bch2_open_buckets_partial_to_text(struct printbuf *out, struct bch_fs *c)
{
	unsigned i;

	out->atomic++;
	spin_lock(&c->freelist_lock);

	for (i = 0; i < c->open_buckets_partial_nr; i++)
		bch2_open_bucket_to_text(out, c,
				c->open_buckets + c->open_buckets_partial[i]);

	spin_unlock(&c->freelist_lock);
	--out->atomic;
}

static const char * const bch2_write_point_states[] = {
#define x(n)	#n,
	WRITE_POINT_STATES()
#undef x
	NULL
};

void bch2_write_points_to_text(struct printbuf *out, struct bch_fs *c)
{
	struct write_point *wp;
	unsigned i;

	for (wp = c->write_points;
	     wp < c->write_points + ARRAY_SIZE(c->write_points);
	     wp++) {
		prt_printf(out, "%lu: ", wp->write_point);
		prt_human_readable_u64(out, wp->sectors_allocated);

		prt_printf(out, " last wrote: ");
		bch2_pr_time_units(out, sched_clock() - wp->last_used);

		for (i = 0; i < WRITE_POINT_STATE_NR; i++) {
			prt_printf(out, " %s: ", bch2_write_point_states[i]);
			bch2_pr_time_units(out, wp->time[i]);
		}

		prt_newline(out);
	}
}