path: root/fs/bcachefs/alloc_foreground.c

/*
 * Primary bucket allocation code
 *
 * Copyright 2012 Google, Inc.
 *
 * Allocation in bcache is done in terms of buckets:
 *
 * Each bucket has associated an 8 bit gen; this gen corresponds to the gen in
 * btree pointers - they must match for the pointer to be considered valid.
 *
 * Thus (assuming a bucket has no dirty data or metadata in it) we can reuse a
 * bucket simply by incrementing its gen.
 *
 * The gens (along with the priorities; it's really the gens are important but
 * the code is named as if it's the priorities) are written in an arbitrary list
 * of buckets on disk, with a pointer to them in the journal header.
 *
 * When we invalidate a bucket, we have to write its new gen to disk and wait
 * for that write to complete before we use it - otherwise after a crash we
 * could have pointers that appeared to be good but pointed to data that had
 * been overwritten.
 *
 * Since the gens and priorities are all stored contiguously on disk, we can
 * batch this up: We fill up the free_inc list with freshly invalidated buckets,
 * call prio_write(), and when prio_write() finishes we pull buckets off the
 * free_inc list and optionally discard them.
 *
 * free_inc isn't the only freelist - if it was, we'd often have to sleep while
 * priorities and gens were being written before we could allocate. c->free is a
 * smaller freelist, and buckets on that list are always ready to be used.
 *
 * If we've got discards enabled, that happens when a bucket moves from the
 * free_inc list to the free list.
 *
 * It's important to ensure that gens don't wrap around - with respect to
 * either the oldest gen in the btree or the gen on disk. This is quite
 * difficult to do in practice, but we explicitly guard against it anyways - if
 * a bucket is in danger of wrapping around we simply skip invalidating it that
 * time around, and we garbage collect or rewrite the priorities sooner than we
 * would have otherwise.
 *
 * 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.
 *
 * invalidate_buckets() drives all the processes described above. It's called
 * from bch2_bucket_alloc() and a few other places that need to make sure free
 * buckets are ready.
 *
 * invalidate_buckets_(lru|fifo)() find buckets that are available to be
 * invalidated, and then invalidate them and stick them on the free_inc list -
 * in either lru or fifo order.
 */

#include "bcachefs.h"
#include "alloc_background.h"
#include "alloc_foreground.h"
#include "btree_gc.h"
#include "buckets.h"
#include "clock.h"
#include "debug.h"
#include "disk_groups.h"
#include "ec.h"
#include "io.h"

#include <linux/math64.h>
#include <linux/rculist.h>
#include <linux/rcupdate.h>
#include <trace/events/bcachefs.h>

enum bucket_alloc_ret {
	ALLOC_SUCCESS,
	OPEN_BUCKETS_EMPTY,
	FREELIST_EMPTY,		/* Allocator thread not keeping up */
};

/*
 * 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_open_bucket_put(struct bch_fs *c, struct open_bucket *ob)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);

	if (ob->ec) {
		bch2_ec_bucket_written(c, ob);
		return;
	}

	percpu_down_read_preempt_disable(&c->usage_lock);
	spin_lock(&ob->lock);

	bch2_mark_alloc_bucket(c, ca, PTR_BUCKET_NR(ca, &ob->ptr),
			       false, gc_pos_alloc(c, ob), 0);
	ob->valid = false;

	spin_unlock(&ob->lock);
	percpu_up_read_preempt_enable(&c->usage_lock);

	spin_lock(&c->freelist_lock);
	ob->freelist = c->open_buckets_freelist;
	c->open_buckets_freelist = ob - c->open_buckets;
	c->open_buckets_nr_free++;
	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->ptr.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);

	c->open_buckets_nr_free--;
	return ob;
}

static void open_bucket_free_unused(struct bch_fs *c,
				    struct open_bucket *ob,
				    bool may_realloc)
{
	struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);

	BUG_ON(ca->open_buckets_partial_nr >=
	       ARRAY_SIZE(ca->open_buckets_partial));

	if (ca->open_buckets_partial_nr <
	    ARRAY_SIZE(ca->open_buckets_partial) &&
	    may_realloc) {
		spin_lock(&c->freelist_lock);
		ob->on_partial_list = true;
		ca->open_buckets_partial[ca->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);
	} else {
		bch2_open_bucket_put(c, ob);
	}
}

static void verify_not_stale(struct bch_fs *c, const struct open_buckets *obs)
{
#ifdef CONFIG_BCACHEFS_DEBUG
	struct open_bucket *ob;
	unsigned i;

	open_bucket_for_each(c, obs, ob, i) {
		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);

		BUG_ON(ptr_stale(ca, &ob->ptr));
	}
#endif
}

/* _only_ for allocating the journal on a new device: */
long bch2_bucket_alloc_new_fs(struct bch_dev *ca)
{
	struct bucket_array *buckets;
	ssize_t b;

	rcu_read_lock();
	buckets = bucket_array(ca);

	for (b = ca->mi.first_bucket; b < ca->mi.nbuckets; b++)
		if (is_available_bucket(buckets->b[b].mark))
			goto success;
	b = -1;
success:
	rcu_read_unlock();
	return b;
}

static inline unsigned open_buckets_reserved(enum alloc_reserve reserve)
{
	switch (reserve) {
	case RESERVE_ALLOC:
		return 0;
	case RESERVE_BTREE:
		return BTREE_NODE_RESERVE / 2;
	default:
		return BTREE_NODE_RESERVE;
	}
}

/**
 * bch_bucket_alloc - allocate a single bucket from a specific device
 *
 * Returns index of bucket on success, 0 on failure
 * */
struct open_bucket *bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
				      enum alloc_reserve reserve,
				      bool may_alloc_partial,
				      struct closure *cl)
{
	struct bucket_array *buckets;
	struct open_bucket *ob;
	long bucket = 0;

	spin_lock(&c->freelist_lock);

	if (may_alloc_partial &&
	    ca->open_buckets_partial_nr) {
		ob = c->open_buckets +
			ca->open_buckets_partial[--ca->open_buckets_partial_nr];
		ob->on_partial_list = false;
		spin_unlock(&c->freelist_lock);
		return ob;
	}

	if (unlikely(c->open_buckets_nr_free <= open_buckets_reserved(reserve))) {
		if (cl)
			closure_wait(&c->open_buckets_wait, cl);
		spin_unlock(&c->freelist_lock);
		trace_open_bucket_alloc_fail(ca, reserve);
		return ERR_PTR(-OPEN_BUCKETS_EMPTY);
	}

	if (likely(fifo_pop(&ca->free[RESERVE_NONE], bucket)))
		goto out;

	switch (reserve) {
	case RESERVE_ALLOC:
		if (fifo_pop(&ca->free[RESERVE_BTREE], bucket))
			goto out;
		break;
	case RESERVE_BTREE:
		if (fifo_used(&ca->free[RESERVE_BTREE]) * 2 >=
		    ca->free[RESERVE_BTREE].size &&
		    fifo_pop(&ca->free[RESERVE_BTREE], bucket))
			goto out;
		break;
	case RESERVE_MOVINGGC:
		if (fifo_pop(&ca->free[RESERVE_MOVINGGC], bucket))
			goto out;
		break;
	default:
		break;
	}

	if (cl)
		closure_wait(&c->freelist_wait, cl);

	spin_unlock(&c->freelist_lock);

	trace_bucket_alloc_fail(ca, reserve);
	return ERR_PTR(-FREELIST_EMPTY);
out:
	verify_not_on_freelist(c, ca, bucket);

	ob = bch2_open_bucket_alloc(c);

	spin_lock(&ob->lock);
	buckets = bucket_array(ca);

	ob->valid	= true;
	ob->sectors_free = ca->mi.bucket_size;
	ob->ptr		= (struct bch_extent_ptr) {
		.gen	= buckets->b[bucket].mark.gen,
		.offset	= bucket_to_sector(ca, bucket),
		.dev	= ca->dev_idx,
	};

	bucket_io_clock_reset(c, ca, bucket, READ);
	bucket_io_clock_reset(c, ca, bucket, WRITE);
	spin_unlock(&ob->lock);

	spin_unlock(&c->freelist_lock);

	bch2_wake_allocator(ca);

	trace_bucket_alloc(ca, reserve);
	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 };
	struct bch_dev *ca;
	unsigned i;

	for_each_member_device_rcu(ca, c, i, devs)
		ret.devs[ret.nr++] = i;

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

void bch2_dev_stripe_increment(struct bch_fs *c, struct bch_dev *ca,
			       struct dev_stripe_state *stripe)
{
	u64 *v = stripe->next_alloc + ca->dev_idx;
	u64 free_space = dev_buckets_free(c, ca);
	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;
}

#define BUCKET_MAY_ALLOC_PARTIAL	(1 << 0)
#define BUCKET_ALLOC_USE_DURABILITY	(1 << 1)

static int bch2_bucket_alloc_set(struct bch_fs *c,
				 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,
				 enum alloc_reserve reserve,
				 unsigned flags,
				 struct closure *cl)
{
	struct dev_alloc_list devs_sorted =
		bch2_dev_alloc_list(c, stripe, devs_may_alloc);
	struct bch_dev *ca;
	bool alloc_failure = false;
	unsigned i, durability;

	BUG_ON(*nr_effective >= nr_replicas);

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

		ca = rcu_dereference(c->devs[devs_sorted.devs[i]]);
		if (!ca)
			continue;

		if (!ca->mi.durability && *have_cache)
			continue;

		ob = bch2_bucket_alloc(c, ca, reserve,
				flags & BUCKET_MAY_ALLOC_PARTIAL, cl);
		if (IS_ERR(ob)) {
			enum bucket_alloc_ret ret = -PTR_ERR(ob);

			WARN_ON(reserve == RESERVE_MOVINGGC &&
				ret != OPEN_BUCKETS_EMPTY);

			if (cl)
				return -EAGAIN;
			if (ret == OPEN_BUCKETS_EMPTY)
				return -ENOSPC;
			alloc_failure = true;
			continue;
		}

		durability = (flags & BUCKET_ALLOC_USE_DURABILITY)
			? ca->mi.durability : 1;

		__clear_bit(ca->dev_idx, devs_may_alloc->d);
		*nr_effective	+= durability;
		*have_cache	|= !durability;

		ob_push(c, ptrs, ob);

		bch2_dev_stripe_increment(c, ca, stripe);

		if (*nr_effective >= nr_replicas)
			return 0;
	}

	return alloc_failure ? -ENOSPC : -EROFS;
}

/* Allocate from stripes: */

/*
 * XXX: use a higher watermark for allocating open buckets here:
 */
static int ec_stripe_alloc(struct bch_fs *c, struct ec_stripe_head *h)
{
	struct bch_devs_mask devs;
	struct open_bucket *ob;
	unsigned i, nr_have = 0, nr_data =
		min_t(unsigned, h->nr_active_devs,
		      EC_STRIPE_MAX) - h->redundancy;
	bool have_cache = true;
	int ret = 0;

	BUG_ON(h->blocks.nr > nr_data);
	BUG_ON(h->parity.nr > h->redundancy);

	devs = h->devs;

	open_bucket_for_each(c, &h->parity, ob, i)
		__clear_bit(ob->ptr.dev, devs.d);
	open_bucket_for_each(c, &h->blocks, ob, i)
		__clear_bit(ob->ptr.dev, devs.d);

	percpu_down_read_preempt_disable(&c->usage_lock);
	rcu_read_lock();

	if (h->parity.nr < h->redundancy) {
		nr_have = h->parity.nr;

		ret = bch2_bucket_alloc_set(c, &h->parity,
					    &h->parity_stripe,
					    &devs,
					    h->redundancy,
					    &nr_have,
					    &have_cache,
					    RESERVE_NONE,
					    0,
					    NULL);
		if (ret)
			goto err;
	}

	if (h->blocks.nr < nr_data) {
		nr_have = h->blocks.nr;

		ret = bch2_bucket_alloc_set(c, &h->blocks,
					    &h->block_stripe,
					    &devs,
					    nr_data,
					    &nr_have,
					    &have_cache,
					    RESERVE_NONE,
					    0,
					    NULL);
		if (ret)
			goto err;
	}

	rcu_read_unlock();
	percpu_up_read_preempt_enable(&c->usage_lock);

	return bch2_ec_stripe_new_alloc(c, h);
err:
	rcu_read_unlock();
	percpu_up_read_preempt_enable(&c->usage_lock);
	return -1;
}

/*
 * 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 void bucket_alloc_from_stripe(struct bch_fs *c,
				     struct open_buckets *ptrs,
				     struct write_point *wp,
				     struct bch_devs_mask *devs_may_alloc,
				     u16 target,
				     unsigned erasure_code,
				     unsigned nr_replicas,
				     unsigned *nr_effective,
				     bool *have_cache)
{
	struct dev_alloc_list devs_sorted;
	struct ec_stripe_head *h;
	struct open_bucket *ob;
	struct bch_dev *ca;
	unsigned i, ec_idx;

	if (!erasure_code)
		return;

	if (nr_replicas < 2)
		return;

	if (ec_open_bucket(c, ptrs))
		return;

	h = bch2_ec_stripe_head_get(c, target, erasure_code, nr_replicas - 1);
	if (!h)
		return;

	if (!h->s && ec_stripe_alloc(c, h))
		goto out_put_head;

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

	for (i = 0; i < devs_sorted.nr; i++)
		open_bucket_for_each(c, &h->s->blocks, ob, ec_idx)
			if (ob->ptr.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->ptr.dev);

	ob->ec_idx	= ec_idx;
	ob->ec		= h->s;

	__clear_bit(ob->ptr.dev, devs_may_alloc->d);
	*nr_effective	+= ca->mi.durability;
	*have_cache	|= !ca->mi.durability;

	ob_push(c, ptrs, ob);
	atomic_inc(&h->s->pin);
out_put_head:
	bch2_ec_stripe_head_put(h);
}

/* Sector allocator */

static void get_buckets_from_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 need_ec)
{
	struct open_buckets ptrs_skip = { .nr = 0 };
	struct open_bucket *ob;
	unsigned i;

	open_bucket_for_each(c, &wp->ptrs, ob, i) {
		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);

		if (*nr_effective < nr_replicas &&
		    test_bit(ob->ptr.dev, devs_may_alloc->d) &&
		    (ca->mi.durability ||
		     (wp->type == BCH_DATA_USER && !*have_cache)) &&
		    (ob->ec || !need_ec)) {
			__clear_bit(ob->ptr.dev, devs_may_alloc->d);
			*nr_effective	+= ca->mi.durability;
			*have_cache	|= !ca->mi.durability;

			ob_push(c, ptrs, ob);
		} else {
			ob_push(c, &ptrs_skip, ob);
		}
	}
	wp->ptrs = ptrs_skip;
}

static int open_bucket_add_buckets(struct bch_fs *c,
				   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 alloc_reserve reserve,
				   struct closure *_cl)
{
	struct bch_devs_mask devs;
	struct open_bucket *ob;
	struct closure *cl = NULL;
	unsigned i, flags = BUCKET_ALLOC_USE_DURABILITY;
	int ret;

	if (wp->type == BCH_DATA_USER)
		flags |= BUCKET_MAY_ALLOC_PARTIAL;

	rcu_read_lock();
	devs = target_rw_devs(c, wp->type, target);
	rcu_read_unlock();

	/* 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->ptr.dev, devs.d);

	if (erasure_code) {
		get_buckets_from_writepoint(c, ptrs, wp, &devs,
					    nr_replicas, nr_effective,
					    have_cache, true);
		if (*nr_effective >= nr_replicas)
			return 0;

		bucket_alloc_from_stripe(c, ptrs, wp, &devs,
					 target, erasure_code,
					 nr_replicas, nr_effective,
					 have_cache);
		if (*nr_effective >= nr_replicas)
			return 0;
	}

	get_buckets_from_writepoint(c, ptrs, wp, &devs,
				    nr_replicas, nr_effective,
				    have_cache, false);
	if (*nr_effective >= nr_replicas)
		return 0;

	percpu_down_read_preempt_disable(&c->usage_lock);
	rcu_read_lock();

retry_blocking:
	/*
	 * Try nonblocking first, so that if one device is full we'll try from
	 * other devices:
	 */
	ret = bch2_bucket_alloc_set(c, ptrs, &wp->stripe, &devs,
				nr_replicas, nr_effective, have_cache,
				reserve, flags, cl);
	if (ret && ret != -EROFS && !cl && _cl) {
		cl = _cl;
		goto retry_blocking;
	}

	rcu_read_unlock();
	percpu_up_read_preempt_enable(&c->usage_lock);

	return ret;
}

void bch2_open_buckets_stop_dev(struct bch_fs *c, struct bch_dev *ca,
				struct open_buckets *obs,
				enum bch_data_type data_type)
{
	struct open_buckets ptrs = { .nr = 0 };
	struct open_bucket *ob, *ob2;
	unsigned i, j;

	open_bucket_for_each(c, obs, ob, i) {
		bool drop = !ca || ob->ptr.dev == ca->dev_idx;

		if (!drop && ob->ec) {
			mutex_lock(&ob->ec->lock);
			open_bucket_for_each(c, &ob->ec->blocks, ob2, j)
				drop |= ob2->ptr.dev == ca->dev_idx;
			open_bucket_for_each(c, &ob->ec->parity, ob2, j)
				drop |= ob2->ptr.dev == ca->dev_idx;
			mutex_unlock(&ob->ec->lock);
		}

		if (drop)
			bch2_open_bucket_put(c, ob);
		else
			ob_push(c, &ptrs, ob);
	}

	*obs = ptrs;
}

void bch2_writepoint_stop(struct bch_fs *c, struct bch_dev *ca,
			  struct write_point *wp)
{
	mutex_lock(&wp->lock);
	bch2_open_buckets_stop_dev(c, ca, &wp->ptrs, wp->type);
	mutex_unlock(&wp->lock);
}

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;

	hlist_for_each_entry_rcu(wp, head, node)
		if (wp->write_point == write_point)
			return wp;

	return NULL;
}

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_sectors_free(c, bch2_fs_usage_read(c));

	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 bch_fs *c,
				     unsigned old_nr)
{
	struct write_point *wp;

	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_writepoint_stop(c, NULL, wp);
	return true;
}

static struct write_point *writepoint_find(struct bch_fs *c,
					   unsigned long write_point)
{
	struct write_point *wp, *oldest;
	struct hlist_head *head;

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

	head = writepoint_hash(c, write_point);
restart_find:
	wp = __writepoint_find(head, write_point);
	if (wp) {
lock_wp:
		mutex_lock(&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;

	mutex_lock(&oldest->lock);
	mutex_lock(&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 = sched_clock();
	return wp;
}

/*
 * Get us an open_bucket we can allocate from, return with it locked:
 */
struct write_point *bch2_alloc_sectors_start(struct bch_fs *c,
				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 alloc_reserve reserve,
				unsigned flags,
				struct closure *cl)
{
	struct write_point *wp;
	struct open_bucket *ob;
	unsigned nr_effective = 0;
	struct open_buckets ptrs = { .nr = 0 };
	bool have_cache = false;
	unsigned write_points_nr;
	int ret = 0, i;

	BUG_ON(!nr_replicas || !nr_replicas_required);
retry:
	write_points_nr = c->write_points_nr;

	wp = writepoint_find(c, write_point.v);

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

	if (!target || (flags & BCH_WRITE_ONLY_SPECIFIED_DEVS)) {
		ret = open_bucket_add_buckets(c, &ptrs, wp, devs_have,
					      target, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, reserve, cl);
	} else {
		ret = open_bucket_add_buckets(c, &ptrs, wp, devs_have,
					      target, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, reserve, NULL);
		if (!ret)
			goto alloc_done;

		ret = open_bucket_add_buckets(c, &ptrs, wp, devs_have,
					      0, erasure_code,
					      nr_replicas, &nr_effective,
					      &have_cache, reserve, 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 == -EROFS &&
	    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->type == BCH_DATA_USER);

	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);

	verify_not_stale(c, &wp->ptrs);

	return wp;
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->type == BCH_DATA_USER);
	wp->ptrs = ptrs;

	mutex_unlock(&wp->lock);

	if (ret == -ENOSPC &&
	    try_decrease_writepoints(c, write_points_nr))
		goto retry;

	return ERR_PTR(ret);
}

/*
 * Append pointers to the space we just allocated to @k, and mark @sectors space
 * as allocated out of @ob
 */
void bch2_alloc_sectors_append_ptrs(struct bch_fs *c, struct write_point *wp,
				    struct bkey_i_extent *e, unsigned sectors)
{
	struct open_bucket *ob;
	unsigned i;

	BUG_ON(sectors > wp->sectors_free);
	wp->sectors_free -= sectors;

	open_bucket_for_each(c, &wp->ptrs, ob, i) {
		struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);
		struct bch_extent_ptr tmp = ob->ptr;

		EBUG_ON(bch2_extent_has_device(extent_i_to_s_c(e), ob->ptr.dev));

		tmp.cached = bkey_extent_is_cached(&e->k) ||
			(!ca->mi.durability && wp->type == BCH_DATA_USER);

		tmp.offset += ca->mi.bucket_size - ob->sectors_free;
		extent_ptr_append(e, tmp);

		BUG_ON(sectors > ob->sectors_free);
		ob->sectors_free -= sectors;
	}
}

/*
 * 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)
{
	struct open_buckets ptrs = { .nr = 0 }, keep = { .nr = 0 };
	struct open_bucket *ob;
	unsigned i;

	open_bucket_for_each(c, &wp->ptrs, ob, i)
		ob_push(c, !ob->sectors_free ? &ptrs : &keep, ob);
	wp->ptrs = keep;

	mutex_unlock(&wp->lock);

	bch2_open_buckets_put(c, &ptrs);
}

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);

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

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