[bcachefs-tools-debian] / libbcachefs / alloc.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.h"
#include "btree_update.h"
#include "buckets.h"
#include "checksum.h"
#include "clock.h"
#include "debug.h"
#include "error.h"
#include "extents.h"
#include "io.h"
#include "journal.h"
#include "super-io.h"

#include <linux/blkdev.h>
#include <linux/kthread.h>
#include <linux/math64.h>
#include <linux/random.h>
#include <linux/rcupdate.h>
#include <linux/sched/task.h>
#include <linux/sort.h>
#include <trace/events/bcachefs.h>

static void bch2_recalc_min_prio(struct bch_dev *, int);

/* Allocation groups: */

void bch2_dev_group_remove(struct dev_group *grp, struct bch_dev *ca)
{
        unsigned i;

        spin_lock(&grp->lock);

        for (i = 0; i < grp->nr; i++)
                if (grp->d[i].dev == ca) {
                        grp->nr--;
                        memmove(&grp->d[i],
                                &grp->d[i + 1],
                                (grp->nr- i) * sizeof(grp->d[0]));
                        break;
                }

        spin_unlock(&grp->lock);
}

void bch2_dev_group_add(struct dev_group *grp, struct bch_dev *ca)
{
        unsigned i;

        spin_lock(&grp->lock);
        for (i = 0; i < grp->nr; i++)
                if (grp->d[i].dev == ca)
                        goto out;

        BUG_ON(grp->nr>= BCH_SB_MEMBERS_MAX);

        grp->d[grp->nr++].dev = ca;
out:
        spin_unlock(&grp->lock);
}

/* Ratelimiting/PD controllers */

static void pd_controllers_update(struct work_struct *work)
{
        struct bch_fs *c = container_of(to_delayed_work(work),
                                           struct bch_fs,
                                           pd_controllers_update);
        struct bch_dev *ca;
        unsigned i, iter;

        /* All units are in bytes */
        u64 faster_tiers_size   = 0;
        u64 faster_tiers_dirty  = 0;

        u64 fastest_tier_size   = 0;
        u64 fastest_tier_free   = 0;
        u64 copygc_can_free     = 0;

        rcu_read_lock();
        for (i = 0; i < ARRAY_SIZE(c->tiers); i++) {
                bch2_pd_controller_update(&c->tiers[i].pd,
                                div_u64(faster_tiers_size *
                                        c->tiering_percent, 100),
                                faster_tiers_dirty,
                                -1);

                spin_lock(&c->tiers[i].devs.lock);
                group_for_each_dev(ca, &c->tiers[i].devs, iter) {
                        struct bch_dev_usage stats = bch2_dev_usage_read(ca);
                        unsigned bucket_bits = ca->bucket_bits + 9;

                        u64 size = (ca->mi.nbuckets -
                                    ca->mi.first_bucket) << bucket_bits;
                        u64 dirty = stats.buckets_dirty << bucket_bits;
                        u64 free = __dev_buckets_free(ca, stats) << bucket_bits;
                        /*
                         * Bytes of internal fragmentation, which can be
                         * reclaimed by copy GC
                         */
                        s64 fragmented = ((stats.buckets_dirty +
                                           stats.buckets_cached) <<
                                          bucket_bits) -
                                ((stats.sectors[S_DIRTY] +
                                  stats.sectors[S_CACHED] ) << 9);

                        fragmented = max(0LL, fragmented);

                        bch2_pd_controller_update(&ca->moving_gc_pd,
                                                 free, fragmented, -1);

                        faster_tiers_size               += size;
                        faster_tiers_dirty              += dirty;

                        if (!c->fastest_tier ||
                            c->fastest_tier == &c->tiers[i]) {
                                fastest_tier_size       += size;
                                fastest_tier_free       += free;
                        }

                        copygc_can_free                 += fragmented;
                }
                spin_unlock(&c->tiers[i].devs.lock);
        }

        rcu_read_unlock();

        /*
         * Throttle foreground writes if tier 0 is running out of free buckets,
         * and either tiering or copygc can free up space.
         *
         * Target will be small if there isn't any work to do - we don't want to
         * throttle foreground writes if we currently have all the free space
         * we're ever going to have.
         *
         * Otherwise, if there's work to do, try to keep 20% of tier0 available
         * for foreground writes.
         */
        if (c->fastest_tier)
                copygc_can_free = U64_MAX;

        bch2_pd_controller_update(&c->foreground_write_pd,
                                 min(copygc_can_free,
                                     div_u64(fastest_tier_size *
                                             c->foreground_target_percent,
                                             100)),
                                 fastest_tier_free,
                                 -1);

        schedule_delayed_work(&c->pd_controllers_update,
                              c->pd_controllers_update_seconds * HZ);
}

static unsigned bch_alloc_val_u64s(const struct bch_alloc *a)
{
        unsigned bytes = offsetof(struct bch_alloc, data);

        if (a->fields & (1 << BCH_ALLOC_FIELD_READ_TIME))
                bytes += 2;
        if (a->fields & (1 << BCH_ALLOC_FIELD_WRITE_TIME))
                bytes += 2;

        return DIV_ROUND_UP(bytes, sizeof(u64));
}

static const char *bch2_alloc_invalid(const struct bch_fs *c,
                                      struct bkey_s_c k)
{
        if (k.k->p.inode >= c->sb.nr_devices ||
            !c->devs[k.k->p.inode])
                return "invalid device";

        switch (k.k->type) {
        case BCH_ALLOC: {
                struct bkey_s_c_alloc a = bkey_s_c_to_alloc(k);

                if (bch_alloc_val_u64s(a.v) != bkey_val_u64s(a.k))
                        return "incorrect value size";
                break;
        }
        default:
                return "invalid type";
        }

        return NULL;
}

static void bch2_alloc_to_text(struct bch_fs *c, char *buf,
                               size_t size, struct bkey_s_c k)
{
        buf[0] = '\0';

        switch (k.k->type) {
        case BCH_ALLOC:
                break;
        }
}

const struct bkey_ops bch2_bkey_alloc_ops = {
        .key_invalid    = bch2_alloc_invalid,
        .val_to_text    = bch2_alloc_to_text,
};

static inline unsigned get_alloc_field(const u8 **p, unsigned bytes)
{
        unsigned v;

        switch (bytes) {
        case 1:
                v = **p;
                break;
        case 2:
                v = le16_to_cpup((void *) *p);
                break;
        case 4:
                v = le32_to_cpup((void *) *p);
                break;
        default:
                BUG();
        }

        *p += bytes;
        return v;
}

static inline void put_alloc_field(u8 **p, unsigned bytes, unsigned v)
{
        switch (bytes) {
        case 1:
                **p = v;
                break;
        case 2:
                *((__le16 *) *p) = cpu_to_le16(v);
                break;
        case 4:
                *((__le32 *) *p) = cpu_to_le32(v);
                break;
        default:
                BUG();
        }

        *p += bytes;
}

static void bch2_alloc_read_key(struct bch_fs *c, struct bkey_s_c k)
{
        struct bch_dev *ca;
        struct bkey_s_c_alloc a;
        struct bucket_mark new;
        struct bucket *g;
        const u8 *d;

        if (k.k->type != BCH_ALLOC)
                return;

        a = bkey_s_c_to_alloc(k);
        ca = c->devs[a.k->p.inode];

        if (a.k->p.offset >= ca->mi.nbuckets)
                return;

        g = ca->buckets + a.k->p.offset;
        bucket_cmpxchg(g, new, ({
                new.gen = a.v->gen;
                new.gen_valid = 1;
        }));

        d = a.v->data;
        if (a.v->fields & (1 << BCH_ALLOC_FIELD_READ_TIME))
                g->prio[READ] = get_alloc_field(&d, 2);
        if (a.v->fields & (1 << BCH_ALLOC_FIELD_WRITE_TIME))
                g->prio[WRITE] = get_alloc_field(&d, 2);
}

int bch2_alloc_read(struct bch_fs *c, struct list_head *journal_replay_list)
{
        struct journal_replay *r;
        struct btree_iter iter;
        struct bkey_s_c k;
        int ret;

        if (!c->btree_roots[BTREE_ID_ALLOC].b)
                return 0;

        for_each_btree_key(&iter, c, BTREE_ID_ALLOC, POS_MIN, 0, k) {
                bch2_alloc_read_key(c, k);
                bch2_btree_iter_cond_resched(&iter);
        }

        ret = bch2_btree_iter_unlock(&iter);
        if (ret)
                return ret;

        list_for_each_entry(r, journal_replay_list, list) {
                struct bkey_i *k, *n;
                struct jset_entry *entry;

                for_each_jset_key(k, n, entry, &r->j)
                        if (entry->btree_id == BTREE_ID_ALLOC)
                                bch2_alloc_read_key(c, bkey_i_to_s_c(k));
        }

        return 0;
}

static int __bch2_alloc_write_key(struct bch_fs *c, struct bch_dev *ca,
                                  struct bucket *g, struct btree_iter *iter,
                                  u64 *journal_seq)
{
        struct bucket_mark m;
        __BKEY_PADDED(k, DIV_ROUND_UP(sizeof(struct bch_alloc), 8)) alloc_key;
        struct bkey_i_alloc *a;
        u8 *d;
        int ret;

        bch2_btree_iter_set_pos(iter, POS(ca->dev_idx, g - ca->buckets));

        do {
                ret = bch2_btree_iter_traverse(iter);
                if (ret)
                        break;

                /* read mark under btree node lock: */
                m = READ_ONCE(g->mark);
                a = bkey_alloc_init(&alloc_key.k);
                a->k.p          = iter->pos;
                a->v.fields     = 0;
                a->v.gen        = m.gen;
                set_bkey_val_u64s(&a->k, bch_alloc_val_u64s(&a->v));

                d = a->v.data;
                if (a->v.fields & (1 << BCH_ALLOC_FIELD_READ_TIME))
                        put_alloc_field(&d, 2, g->prio[READ]);
                if (a->v.fields & (1 << BCH_ALLOC_FIELD_WRITE_TIME))
                        put_alloc_field(&d, 2, g->prio[WRITE]);

                bch2_btree_iter_set_pos(iter, a->k.p);
                ret = bch2_btree_insert_at(c, NULL, NULL, journal_seq,
                                           BTREE_INSERT_ATOMIC|
                                           BTREE_INSERT_NOFAIL|
                                           BTREE_INSERT_USE_RESERVE|
                                           BTREE_INSERT_USE_ALLOC_RESERVE|
                                           BTREE_INSERT_NOWAIT,
                                           BTREE_INSERT_ENTRY(iter, &a->k_i));
                bch2_btree_iter_cond_resched(iter);
        } while (ret == -EINTR);

        return ret;
}

int bch2_alloc_replay_key(struct bch_fs *c, struct bpos pos)
{
        struct bch_dev *ca;
        struct bucket *g;
        struct btree_iter iter;
        int ret;

        if (pos.inode >= c->sb.nr_devices || !c->devs[pos.inode])
                return 0;

        ca = c->devs[pos.inode];

        if (pos.offset >= ca->mi.nbuckets)
                return 0;

        g = ca->buckets + pos.offset;

        bch2_btree_iter_init(&iter, c, BTREE_ID_ALLOC, POS_MIN,
                             BTREE_ITER_INTENT);

        ret = __bch2_alloc_write_key(c, ca, g, &iter, NULL);
        bch2_btree_iter_unlock(&iter);
        return ret;
}

int bch2_alloc_write(struct bch_fs *c, struct bch_dev *ca, u64 *journal_seq)
{
        struct btree_iter iter;
        struct bucket *g;
        int ret = 0;

        bch2_btree_iter_init(&iter, c, BTREE_ID_ALLOC, POS_MIN,
                             BTREE_ITER_INTENT);

        for_each_bucket(g, ca) {
                ret = __bch2_alloc_write_key(c, ca, g, &iter, journal_seq);
                if (ret)
                        break;
        }

        bch2_btree_iter_unlock(&iter);
        return ret;
}

#define BUCKET_GC_GEN_MAX       96U

/**
 * wait_buckets_available - wait on reclaimable buckets
 *
 * If there aren't enough available buckets to fill up free_inc, wait until
 * there are.
 */
static int wait_buckets_available(struct bch_fs *c, struct bch_dev *ca)
{
        unsigned long gc_count = c->gc_count;
        int ret = 0;

        while (1) {
                set_current_state(TASK_INTERRUPTIBLE);
                if (kthread_should_stop()) {
                        ret = -1;
                        break;
                }

                if (gc_count != c->gc_count)
                        ca->inc_gen_really_needs_gc = 0;

                if ((ssize_t) (dev_buckets_available(ca) -
                               ca->inc_gen_really_needs_gc) >=
                    (ssize_t) fifo_free(&ca->free_inc))
                        break;

                up_read(&c->gc_lock);
                schedule();
                try_to_freeze();
                down_read(&c->gc_lock);
        }

        __set_current_state(TASK_RUNNING);
        return ret;
}

static void verify_not_on_freelist(struct bch_dev *ca, size_t bucket)
{
        if (expensive_debug_checks(ca->fs)) {
                size_t iter;
                long i;
                unsigned j;

                for (j = 0; j < RESERVE_NR; j++)
                        fifo_for_each_entry(i, &ca->free[j], iter)
                                BUG_ON(i == bucket);
                fifo_for_each_entry(i, &ca->free_inc, iter)
                        BUG_ON(i == bucket);
        }
}

/* Bucket heap / gen */

void bch2_recalc_min_prio(struct bch_dev *ca, int rw)
{
        struct bch_fs *c = ca->fs;
        struct prio_clock *clock = &c->prio_clock[rw];
        struct bucket *g;
        u16 max_delta = 1;
        unsigned i;

        lockdep_assert_held(&c->bucket_lock);

        /* Determine min prio for this particular cache */
        for_each_bucket(g, ca)
                max_delta = max(max_delta, (u16) (clock->hand - g->prio[rw]));

        ca->min_prio[rw] = clock->hand - max_delta;

        /*
         * This may possibly increase the min prio for the whole cache, check
         * that as well.
         */
        max_delta = 1;

        for_each_member_device(ca, c, i)
                max_delta = max(max_delta,
                                (u16) (clock->hand - ca->min_prio[rw]));

        clock->min_prio = clock->hand - max_delta;
}

static void bch2_rescale_prios(struct bch_fs *c, int rw)
{
        struct prio_clock *clock = &c->prio_clock[rw];
        struct bch_dev *ca;
        struct bucket *g;
        unsigned i;

        trace_rescale_prios(c);

        for_each_member_device(ca, c, i) {
                for_each_bucket(g, ca)
                        g->prio[rw] = clock->hand -
                                (clock->hand - g->prio[rw]) / 2;

                bch2_recalc_min_prio(ca, rw);
        }
}

static void bch2_inc_clock_hand(struct io_timer *timer)
{
        struct prio_clock *clock = container_of(timer,
                                        struct prio_clock, rescale);
        struct bch_fs *c = container_of(clock,
                                struct bch_fs, prio_clock[clock->rw]);
        u64 capacity;

        mutex_lock(&c->bucket_lock);

        clock->hand++;

        /* if clock cannot be advanced more, rescale prio */
        if (clock->hand == (u16) (clock->min_prio - 1))
                bch2_rescale_prios(c, clock->rw);

        mutex_unlock(&c->bucket_lock);

        capacity = READ_ONCE(c->capacity);

        if (!capacity)
                return;

        /*
         * we only increment when 0.1% of the filesystem capacity has been read
         * or written too, this determines if it's time
         *
         * XXX: we shouldn't really be going off of the capacity of devices in
         * RW mode (that will be 0 when we're RO, yet we can still service
         * reads)
         */
        timer->expire += capacity >> 10;

        bch2_io_timer_add(&c->io_clock[clock->rw], timer);
}

static void bch2_prio_timer_init(struct bch_fs *c, int rw)
{
        struct prio_clock *clock = &c->prio_clock[rw];
        struct io_timer *timer = &clock->rescale;

        clock->rw       = rw;
        timer->fn       = bch2_inc_clock_hand;
        timer->expire   = c->capacity >> 10;
}

/*
 * Background allocation thread: scans for buckets to be invalidated,
 * invalidates them, rewrites prios/gens (marking them as invalidated on disk),
 * then optionally issues discard commands to the newly free buckets, then puts
 * them on the various freelists.
 */

static inline bool can_inc_bucket_gen(struct bch_dev *ca, struct bucket *g)
{
        return bucket_gc_gen(ca, g) < BUCKET_GC_GEN_MAX;
}

static bool bch2_can_invalidate_bucket(struct bch_dev *ca, struct bucket *g,
                                       struct bucket_mark mark)
{
        if (!is_available_bucket(mark))
                return false;

        if (bucket_gc_gen(ca, g) >= BUCKET_GC_GEN_MAX / 2)
                ca->inc_gen_needs_gc++;

        if (bucket_gc_gen(ca, g) >= BUCKET_GC_GEN_MAX)
                ca->inc_gen_really_needs_gc++;

        return can_inc_bucket_gen(ca, g);
}

static void bch2_invalidate_one_bucket(struct bch_dev *ca, struct bucket *g)
{
        struct bch_fs *c = ca->fs;
        struct bucket_mark m;

        spin_lock(&ca->freelist_lock);
        if (!bch2_invalidate_bucket(ca, g, &m)) {
                spin_unlock(&ca->freelist_lock);
                return;
        }

        verify_not_on_freelist(ca, g - ca->buckets);
        BUG_ON(!fifo_push(&ca->free_inc, g - ca->buckets));
        spin_unlock(&ca->freelist_lock);

        g->prio[READ] = c->prio_clock[READ].hand;
        g->prio[WRITE] = c->prio_clock[WRITE].hand;

        if (m.cached_sectors) {
                ca->allocator_invalidating_data = true;
        } else if (m.journal_seq_valid) {
                u64 journal_seq = atomic64_read(&c->journal.seq);
                u64 bucket_seq  = journal_seq;

                bucket_seq &= ~((u64) U16_MAX);
                bucket_seq |= m.journal_seq;

                if (bucket_seq > journal_seq)
                        bucket_seq -= 1 << 16;

                ca->allocator_journal_seq_flush =
                        max(ca->allocator_journal_seq_flush, bucket_seq);
        }
}

/*
 * Determines what order we're going to reuse buckets, smallest bucket_key()
 * first.
 *
 *
 * - We take into account the read prio of the bucket, which gives us an
 *   indication of how hot the data is -- we scale the prio so that the prio
 *   farthest from the clock is worth 1/8th of the closest.
 *
 * - The number of sectors of cached data in the bucket, which gives us an
 *   indication of the cost in cache misses this eviction will cause.
 *
 * - If hotness * sectors used compares equal, we pick the bucket with the
 *   smallest bucket_gc_gen() - since incrementing the same bucket's generation
 *   number repeatedly forces us to run mark and sweep gc to avoid generation
 *   number wraparound.
 */

static unsigned long bucket_sort_key(struct bch_dev *ca,
                                     struct bucket *g,
                                     struct bucket_mark m)
{
        /*
         * Time since last read, scaled to [0, 8) where larger value indicates
         * more recently read data:
         */
        unsigned long hotness =
                (g->prio[READ]                  - ca->min_prio[READ]) * 7 /
                (ca->fs->prio_clock[READ].hand  - ca->min_prio[READ]);

        /* How much we want to keep the data in this bucket: */
        unsigned long data_wantness =
                (hotness + 1) * bucket_sectors_used(m);

        unsigned long needs_journal_commit =
                    bucket_needs_journal_commit(m, ca->fs->journal.last_seq_ondisk);

        return  (data_wantness << 9) |
                (needs_journal_commit << 8) |
                bucket_gc_gen(ca, g);
}

static inline int bucket_alloc_cmp(alloc_heap *h,
                                   struct alloc_heap_entry l,
                                   struct alloc_heap_entry r)
{
        return (l.key > r.key) - (l.key < r.key);
}

static void invalidate_buckets_lru(struct bch_dev *ca)
{
        struct alloc_heap_entry e;
        struct bucket *g;

        ca->alloc_heap.used = 0;

        mutex_lock(&ca->fs->bucket_lock);
        bch2_recalc_min_prio(ca, READ);
        bch2_recalc_min_prio(ca, WRITE);

        /*
         * Find buckets with lowest read priority, by building a maxheap sorted
         * by read priority and repeatedly replacing the maximum element until
         * all buckets have been visited.
         */
        for_each_bucket(g, ca) {
                struct bucket_mark m = READ_ONCE(g->mark);

                if (!bch2_can_invalidate_bucket(ca, g, m))
                        continue;

                e = (struct alloc_heap_entry) {
                        .bucket = g - ca->buckets,
                        .key    = bucket_sort_key(ca, g, m)
                };

                heap_add_or_replace(&ca->alloc_heap, e, -bucket_alloc_cmp);
        }

        heap_resort(&ca->alloc_heap, bucket_alloc_cmp);

        /*
         * If we run out of buckets to invalidate, bch2_allocator_thread() will
         * kick stuff and retry us
         */
        while (!fifo_full(&ca->free_inc) &&
               heap_pop(&ca->alloc_heap, e, bucket_alloc_cmp))
                bch2_invalidate_one_bucket(ca, &ca->buckets[e.bucket]);

        mutex_unlock(&ca->fs->bucket_lock);
}

static void invalidate_buckets_fifo(struct bch_dev *ca)
{
        struct bucket_mark m;
        struct bucket *g;
        size_t checked = 0;

        while (!fifo_full(&ca->free_inc)) {
                if (ca->fifo_last_bucket <  ca->mi.first_bucket ||
                    ca->fifo_last_bucket >= ca->mi.nbuckets)
                        ca->fifo_last_bucket = ca->mi.first_bucket;

                g = ca->buckets + ca->fifo_last_bucket++;
                m = READ_ONCE(g->mark);

                if (bch2_can_invalidate_bucket(ca, g, m))
                        bch2_invalidate_one_bucket(ca, g);

                if (++checked >= ca->mi.nbuckets)
                        return;
        }
}

static void invalidate_buckets_random(struct bch_dev *ca)
{
        struct bucket_mark m;
        struct bucket *g;
        size_t checked = 0;

        while (!fifo_full(&ca->free_inc)) {
                size_t n = bch2_rand_range(ca->mi.nbuckets -
                                          ca->mi.first_bucket) +
                        ca->mi.first_bucket;

                g = ca->buckets + n;
                m = READ_ONCE(g->mark);

                if (bch2_can_invalidate_bucket(ca, g, m))
                        bch2_invalidate_one_bucket(ca, g);

                if (++checked >= ca->mi.nbuckets / 2)
                        return;
        }
}

static void invalidate_buckets(struct bch_dev *ca)
{
        ca->inc_gen_needs_gc                    = 0;
        ca->inc_gen_really_needs_gc             = 0;

        switch (ca->mi.replacement) {
        case CACHE_REPLACEMENT_LRU:
                invalidate_buckets_lru(ca);
                break;
        case CACHE_REPLACEMENT_FIFO:
                invalidate_buckets_fifo(ca);
                break;
        case CACHE_REPLACEMENT_RANDOM:
                invalidate_buckets_random(ca);
                break;
        }
}

static int size_t_cmp(const void *_l, const void *_r)
{
        const size_t *l = _l, *r = _r;

        return (*l > *r) - (*l < *r);
}

static int bch2_invalidate_free_inc(struct bch_fs *c, struct bch_dev *ca,
                                    u64 *journal_seq)
{
        struct btree_iter iter;
        unsigned nr_invalidated = 0;
        size_t b, i;
        int ret = 0;

        bch2_btree_iter_init(&iter, c, BTREE_ID_ALLOC, POS(ca->dev_idx, 0),
                             BTREE_ITER_INTENT);

        fifo_for_each_entry(b, &ca->free_inc, i) {
                ret = __bch2_alloc_write_key(c, ca, ca->buckets + b,
                                             &iter, journal_seq);
                if (ret)
                        break;

                nr_invalidated++;
        }

        bch2_btree_iter_unlock(&iter);
        return nr_invalidated ?: ret;
}

/*
 * Given an invalidated, ready to use bucket: issue a discard to it if enabled,
 * then add it to the freelist, waiting until there's room if necessary:
 */
static void discard_invalidated_bucket(struct bch_dev *ca, long bucket)
{
        if (ca->mi.discard &&
            blk_queue_discard(bdev_get_queue(ca->disk_sb.bdev)))
                blkdev_issue_discard(ca->disk_sb.bdev,
                                     bucket_to_sector(ca, bucket),
                                     ca->mi.bucket_size, GFP_NOIO, 0);

        while (1) {
                bool pushed = false;
                unsigned i;

                set_current_state(TASK_INTERRUPTIBLE);

                /*
                 * Don't remove from free_inc until after it's added to
                 * freelist, so gc can find it:
                 */
                spin_lock(&ca->freelist_lock);
                for (i = 0; i < RESERVE_NR; i++)
                        if (fifo_push(&ca->free[i], bucket)) {
                                fifo_pop(&ca->free_inc, bucket);
                                closure_wake_up(&ca->fs->freelist_wait);
                                pushed = true;
                                break;
                        }
                spin_unlock(&ca->freelist_lock);

                if (pushed)
                        break;

                if (kthread_should_stop())
                        break;

                schedule();
                try_to_freeze();
        }

        __set_current_state(TASK_RUNNING);
}

/**
 * bch_allocator_thread - move buckets from free_inc to reserves
 *
 * The free_inc FIFO is populated by invalidate_buckets(), and
 * the reserves are depleted by bucket allocation. When we run out
 * of free_inc, try to invalidate some buckets and write out
 * prios and gens.
 */
static int bch2_allocator_thread(void *arg)
{
        struct bch_dev *ca = arg;
        struct bch_fs *c = ca->fs;
        u64 journal_seq;
        size_t bucket;
        int ret;

        set_freezable();

        while (1) {
                while (1) {
                        while (ca->nr_invalidated) {
                                BUG_ON(fifo_empty(&ca->free_inc));

                                bucket = fifo_peek(&ca->free_inc);
                                discard_invalidated_bucket(ca, bucket);
                                if (kthread_should_stop())
                                        goto out;
                                --ca->nr_invalidated;
                        }

                        if (fifo_empty(&ca->free_inc))
                                break;

                        journal_seq = 0;
                        ret = bch2_invalidate_free_inc(c, ca, &journal_seq);
                        if (ret < 0)
                                goto out;

                        ca->nr_invalidated = ret;

                        if (ca->nr_invalidated == fifo_used(&ca->free_inc))
                                ca->alloc_thread_started = true;

                        if (ca->allocator_invalidating_data)
                                bch2_journal_flush_seq(&c->journal, journal_seq);
                        else if (ca->allocator_journal_seq_flush)
                                bch2_journal_flush_seq(&c->journal,
                                                       ca->allocator_journal_seq_flush);
                }

                /* Reset front/back so we can easily sort fifo entries later: */
                ca->free_inc.front = ca->free_inc.back  = 0;
                ca->allocator_journal_seq_flush         = 0;
                ca->allocator_invalidating_data         = false;

                down_read(&c->gc_lock);
                if (test_bit(BCH_FS_GC_FAILURE, &c->flags)) {
                        up_read(&c->gc_lock);
                        goto out;
                }

                while (1) {
                        /*
                         * Find some buckets that we can invalidate, either
                         * they're completely unused, or only contain clean data
                         * that's been written back to the backing device or
                         * another cache tier
                         */

                        invalidate_buckets(ca);
                        trace_alloc_batch(ca, fifo_used(&ca->free_inc),
                                          ca->free_inc.size);

                        if ((ca->inc_gen_needs_gc >= ca->free_inc.size ||
                             (!fifo_full(&ca->free_inc) &&
                              ca->inc_gen_really_needs_gc >=
                              fifo_free(&ca->free_inc))) &&
                            c->gc_thread) {
                                atomic_inc(&c->kick_gc);
                                wake_up_process(c->gc_thread);
                        }

                        if (fifo_full(&ca->free_inc))
                                break;

                        if (wait_buckets_available(c, ca)) {
                                up_read(&c->gc_lock);
                                goto out;
                        }
                }
                up_read(&c->gc_lock);

                BUG_ON(ca->free_inc.front);

                spin_lock(&ca->freelist_lock);
                sort(ca->free_inc.data,
                     ca->free_inc.back,
                     sizeof(ca->free_inc.data[0]),
                     size_t_cmp, NULL);
                spin_unlock(&ca->freelist_lock);

                /*
                 * free_inc is now full of newly-invalidated buckets: next,
                 * write out the new bucket gens:
                 */
        }
out:
        /*
         * Avoid a race with bch2_usage_update() trying to wake us up after
         * we've exited:
         */
        synchronize_rcu();
        return 0;
}

/* Allocation */

static long bch2_bucket_alloc_startup(struct bch_fs *c, struct bch_dev *ca)
{
        struct bucket *g;
        long r = -1;

        if (!down_read_trylock(&c->gc_lock))
                return r;

        if (test_bit(BCH_FS_GC_FAILURE, &c->flags))
                goto out;

        for_each_bucket(g, ca)
                if (!g->mark.touched_this_mount &&
                    is_available_bucket(g->mark) &&
                    bch2_mark_alloc_bucket_startup(ca, g)) {
                        r = g - ca->buckets;
                        break;
                }
out:
        up_read(&c->gc_lock);
        return r;
}

/**
 * bch_bucket_alloc - allocate a single bucket from a specific device
 *
 * Returns index of bucket on success, 0 on failure
 * */
long bch2_bucket_alloc(struct bch_fs *c, struct bch_dev *ca,
                       enum alloc_reserve reserve)
{
        size_t r;

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

        switch (reserve) {
        case RESERVE_ALLOC:
                if (fifo_pop(&ca->free[RESERVE_BTREE], r))
                        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], r))
                        goto out;
                break;
        case RESERVE_MOVINGGC:
                if (fifo_pop(&ca->free[RESERVE_MOVINGGC], r))
                        goto out;
                break;
        default:
                break;
        }

        spin_unlock(&ca->freelist_lock);

        if (unlikely(!ca->alloc_thread_started) &&
            (r = bch2_bucket_alloc_startup(c, ca)) >= 0) {
                verify_not_on_freelist(ca, r);
                goto out2;
        }

        trace_bucket_alloc_fail(ca, reserve);
        return -1;
out:
        verify_not_on_freelist(ca, r);
        spin_unlock(&ca->freelist_lock);

        bch2_wake_allocator(ca);
out2:
        ca->buckets[r].prio[READ]       = c->prio_clock[READ].hand;
        ca->buckets[r].prio[WRITE]      = c->prio_clock[WRITE].hand;

        trace_bucket_alloc(ca, reserve);
        return r;
}

enum bucket_alloc_ret {
        ALLOC_SUCCESS,
        NO_DEVICES,             /* -EROFS */
        FREELIST_EMPTY,         /* Allocator thread not keeping up */
};

static void recalc_alloc_group_weights(struct bch_fs *c,
                                       struct dev_group *devs)
{
        struct bch_dev *ca;
        u64 available_buckets = 1; /* avoid a divide by zero... */
        unsigned i;

        for (i = 0; i < devs->nr; i++) {
                ca = devs->d[i].dev;

                devs->d[i].weight = dev_buckets_free(ca);
                available_buckets += devs->d[i].weight;
        }

        for (i = 0; i < devs->nr; i++) {
                const unsigned min_weight = U32_MAX >> 4;
                const unsigned max_weight = U32_MAX;

                devs->d[i].weight =
                        min_weight +
                        div64_u64(devs->d[i].weight *
                                  devs->nr *
                                  (max_weight - min_weight),
                                  available_buckets);
                devs->d[i].weight = min_t(u64, devs->d[i].weight, max_weight);
        }
}

static enum bucket_alloc_ret bch2_bucket_alloc_group(struct bch_fs *c,
                                                    struct open_bucket *ob,
                                                    enum alloc_reserve reserve,
                                                    unsigned nr_replicas,
                                                    struct dev_group *devs,
                                                    long *devs_used)
{
        enum bucket_alloc_ret ret;
        unsigned fail_idx = -1, i;
        unsigned available = 0;

        BUG_ON(nr_replicas > ARRAY_SIZE(ob->ptrs));

        if (ob->nr_ptrs >= nr_replicas)
                return ALLOC_SUCCESS;

        spin_lock(&devs->lock);

        for (i = 0; i < devs->nr; i++)
                available += !test_bit(devs->d[i].dev->dev_idx,
                                       devs_used);

        recalc_alloc_group_weights(c, devs);

        i = devs->cur_device;

        while (ob->nr_ptrs < nr_replicas) {
                struct bch_dev *ca;
                long bucket;

                if (!available) {
                        ret = NO_DEVICES;
                        goto err;
                }

                i++;
                i %= devs->nr;

                ret = FREELIST_EMPTY;
                if (i == fail_idx)
                        goto err;

                ca = devs->d[i].dev;

                if (test_bit(ca->dev_idx, devs_used))
                        continue;

                if (fail_idx == -1 &&
                    get_random_int() > devs->d[i].weight)
                        continue;

                bucket = bch2_bucket_alloc(c, ca, reserve);
                if (bucket < 0) {
                        if (fail_idx == -1)
                                fail_idx = i;
                        continue;
                }

                /*
                 * open_bucket_add_buckets expects new pointers at the head of
                 * the list:
                 */
                memmove(&ob->ptrs[1],
                        &ob->ptrs[0],
                        ob->nr_ptrs * sizeof(ob->ptrs[0]));
                memmove(&ob->ptr_offset[1],
                        &ob->ptr_offset[0],
                        ob->nr_ptrs * sizeof(ob->ptr_offset[0]));
                ob->nr_ptrs++;
                ob->ptrs[0] = (struct bch_extent_ptr) {
                        .gen    = ca->buckets[bucket].mark.gen,
                        .offset = bucket_to_sector(ca, bucket),
                        .dev    = ca->dev_idx,
                };
                ob->ptr_offset[0] = 0;

                __set_bit(ca->dev_idx, devs_used);
                available--;
                devs->cur_device = i;
        }

        ret = ALLOC_SUCCESS;
err:
        EBUG_ON(ret != ALLOC_SUCCESS && reserve == RESERVE_MOVINGGC);
        spin_unlock(&devs->lock);
        return ret;
}

static enum bucket_alloc_ret __bch2_bucket_alloc_set(struct bch_fs *c,
                                                    struct write_point *wp,
                                                    struct open_bucket *ob,
                                                    unsigned nr_replicas,
                                                    enum alloc_reserve reserve,
                                                    long *devs_used)
{
        struct bch_tier *tier;
        /*
         * this should implement policy - for a given type of allocation, decide
         * which devices to allocate from:
         *
         * XXX: switch off wp->type and do something more intelligent here
         */
        if (wp->group)
                return bch2_bucket_alloc_group(c, ob, reserve, nr_replicas,
                                              wp->group, devs_used);

        /* foreground writes: prefer fastest tier: */
        tier = READ_ONCE(c->fastest_tier);
        if (tier)
                bch2_bucket_alloc_group(c, ob, reserve, nr_replicas,
                                       &tier->devs, devs_used);

        return bch2_bucket_alloc_group(c, ob, reserve, nr_replicas,
                                      &c->all_devs, devs_used);
}

static int bch2_bucket_alloc_set(struct bch_fs *c, struct write_point *wp,
                                struct open_bucket *ob, unsigned nr_replicas,
                                enum alloc_reserve reserve, long *devs_used,
                                struct closure *cl)
{
        bool waiting = false;

        while (1) {
                switch (__bch2_bucket_alloc_set(c, wp, ob, nr_replicas,
                                               reserve, devs_used)) {
                case ALLOC_SUCCESS:
                        if (waiting)
                                closure_wake_up(&c->freelist_wait);

                        return 0;

                case NO_DEVICES:
                        if (waiting)
                                closure_wake_up(&c->freelist_wait);
                        return -EROFS;

                case FREELIST_EMPTY:
                        if (!cl || waiting)
                                trace_freelist_empty_fail(c,
                                                        reserve, cl);

                        if (!cl)
                                return -ENOSPC;

                        if (waiting)
                                return -EAGAIN;

                        /* Retry allocation after adding ourself to waitlist: */
                        closure_wait(&c->freelist_wait, cl);
                        waiting = true;
                        break;
                default:
                        BUG();
                }
        }
}

/* Open buckets: */

/*
 * Open buckets represent one or more buckets (on multiple devices) that are
 * 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.
 */

static void __bch2_open_bucket_put(struct bch_fs *c, struct open_bucket *ob)
{
        const struct bch_extent_ptr *ptr;

        lockdep_assert_held(&c->open_buckets_lock);

        open_bucket_for_each_ptr(ob, ptr) {
                struct bch_dev *ca = c->devs[ptr->dev];

                bch2_mark_alloc_bucket(ca, PTR_BUCKET(ca, ptr), false);
        }

        ob->nr_ptrs = 0;

        list_move(&ob->list, &c->open_buckets_free);
        c->open_buckets_nr_free++;
        closure_wake_up(&c->open_buckets_wait);
}

void bch2_open_bucket_put(struct bch_fs *c, struct open_bucket *b)
{
        if (atomic_dec_and_test(&b->pin)) {
                spin_lock(&c->open_buckets_lock);
                __bch2_open_bucket_put(c, b);
                spin_unlock(&c->open_buckets_lock);
        }
}

static struct open_bucket *bch2_open_bucket_get(struct bch_fs *c,
                                               unsigned nr_reserved,
                                               struct closure *cl)
{
        struct open_bucket *ret;

        spin_lock(&c->open_buckets_lock);

        if (c->open_buckets_nr_free > nr_reserved) {
                BUG_ON(list_empty(&c->open_buckets_free));
                ret = list_first_entry(&c->open_buckets_free,
                                       struct open_bucket, list);
                list_move(&ret->list, &c->open_buckets_open);
                BUG_ON(ret->nr_ptrs);

                atomic_set(&ret->pin, 1); /* XXX */
                ret->has_full_ptrs      = false;

                c->open_buckets_nr_free--;
                trace_open_bucket_alloc(c, cl);
        } else {
                trace_open_bucket_alloc_fail(c, cl);

                if (cl) {
                        closure_wait(&c->open_buckets_wait, cl);
                        ret = ERR_PTR(-EAGAIN);
                } else
                        ret = ERR_PTR(-ENOSPC);
        }

        spin_unlock(&c->open_buckets_lock);

        return ret;
}

static unsigned ob_ptr_sectors_free(struct bch_fs *c,
                                    struct open_bucket *ob,
                                    struct bch_extent_ptr *ptr)
{
        struct bch_dev *ca = c->devs[ptr->dev];
        unsigned i = ptr - ob->ptrs;
        unsigned bucket_size = ca->mi.bucket_size;
        unsigned used = (ptr->offset & (bucket_size - 1)) +
                ob->ptr_offset[i];

        BUG_ON(used > bucket_size);

        return bucket_size - used;
}

static unsigned open_bucket_sectors_free(struct bch_fs *c,
                                         struct open_bucket *ob,
                                         unsigned nr_replicas)
{
        unsigned i, sectors_free = UINT_MAX;

        for (i = 0; i < min(nr_replicas, ob->nr_ptrs); i++)
                sectors_free = min(sectors_free,
                                   ob_ptr_sectors_free(c, ob, &ob->ptrs[i]));

        return sectors_free != UINT_MAX ? sectors_free : 0;
}

static void open_bucket_copy_unused_ptrs(struct bch_fs *c,
                                         struct open_bucket *new,
                                         struct open_bucket *old)
{
        unsigned i;

        for (i = 0; i < old->nr_ptrs; i++)
                if (ob_ptr_sectors_free(c, old, &old->ptrs[i])) {
                        struct bch_extent_ptr tmp = old->ptrs[i];

                        tmp.offset += old->ptr_offset[i];
                        new->ptrs[new->nr_ptrs] = tmp;
                        new->ptr_offset[new->nr_ptrs] = 0;
                        new->nr_ptrs++;
                }
}

static void verify_not_stale(struct bch_fs *c, const struct open_bucket *ob)
{
#ifdef CONFIG_BCACHEFS_DEBUG
        const struct bch_extent_ptr *ptr;

        open_bucket_for_each_ptr(ob, ptr) {
                struct bch_dev *ca = c->devs[ptr->dev];

                BUG_ON(ptr_stale(ca, ptr));
        }
#endif
}

/* Sector allocator */

static struct open_bucket *lock_writepoint(struct bch_fs *c,
                                           struct write_point *wp)
{
        struct open_bucket *ob;

        while ((ob = ACCESS_ONCE(wp->b))) {
                mutex_lock(&ob->lock);
                if (wp->b == ob)
                        break;

                mutex_unlock(&ob->lock);
        }

        return ob;
}

static int open_bucket_add_buckets(struct bch_fs *c,
                                   struct write_point *wp,
                                   struct open_bucket *ob,
                                   unsigned nr_replicas,
                                   unsigned nr_replicas_required,
                                   enum alloc_reserve reserve,
                                   struct closure *cl)
{
        long devs_used[BITS_TO_LONGS(BCH_SB_MEMBERS_MAX)];
        unsigned i;
        int ret;

        /*
         * We might be allocating pointers to add to an existing extent
         * (tiering/copygc/migration) - if so, some of the pointers in our
         * existing open bucket might duplicate devices we already have. This is
         * moderately annoying.
         */

        /* Short circuit all the fun stuff if posssible: */
        if (ob->nr_ptrs >= nr_replicas)
                return 0;

        memset(devs_used, 0, sizeof(devs_used));

        for (i = 0; i < ob->nr_ptrs; i++)
                __set_bit(ob->ptrs[i].dev, devs_used);

        ret = bch2_bucket_alloc_set(c, wp, ob, nr_replicas,
                                   reserve, devs_used, cl);

        if (ret == -EROFS &&
            ob->nr_ptrs >= nr_replicas_required)
                ret = 0;

        return ret;
}

/*
 * Get us an open_bucket we can allocate from, return with it locked:
 */
struct open_bucket *bch2_alloc_sectors_start(struct bch_fs *c,
                                             struct write_point *wp,
                                             unsigned nr_replicas,
                                             unsigned nr_replicas_required,
                                             enum alloc_reserve reserve,
                                             struct closure *cl)
{
        struct open_bucket *ob;
        unsigned open_buckets_reserved = wp == &c->btree_write_point
                ? 0 : BTREE_NODE_RESERVE;
        int ret;

        BUG_ON(!nr_replicas);
retry:
        ob = lock_writepoint(c, wp);

        /*
         * If ob->sectors_free == 0, one or more of the buckets ob points to is
         * full. We can't drop pointers from an open bucket - garbage collection
         * still needs to find them; instead, we must allocate a new open bucket
         * and copy any pointers to non-full buckets into the new open bucket.
         */
        if (!ob || ob->has_full_ptrs) {
                struct open_bucket *new_ob;

                new_ob = bch2_open_bucket_get(c, open_buckets_reserved, cl);
                if (IS_ERR(new_ob))
                        return new_ob;

                mutex_lock(&new_ob->lock);

                /*
                 * We point the write point at the open_bucket before doing the
                 * allocation to avoid a race with shutdown:
                 */
                if (race_fault() ||
                    cmpxchg(&wp->b, ob, new_ob) != ob) {
                        /* We raced: */
                        mutex_unlock(&new_ob->lock);
                        bch2_open_bucket_put(c, new_ob);

                        if (ob)
                                mutex_unlock(&ob->lock);
                        goto retry;
                }

                if (ob) {
                        open_bucket_copy_unused_ptrs(c, new_ob, ob);
                        mutex_unlock(&ob->lock);
                        bch2_open_bucket_put(c, ob);
                }

                ob = new_ob;
        }

        ret = open_bucket_add_buckets(c, wp, ob, nr_replicas,
                                      nr_replicas_required,
                                      reserve, cl);
        if (ret) {
                mutex_unlock(&ob->lock);
                return ERR_PTR(ret);
        }

        ob->sectors_free = open_bucket_sectors_free(c, ob, nr_replicas);

        BUG_ON(!ob->sectors_free);
        verify_not_stale(c, ob);

        return ob;
}

/*
 * 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 bkey_i_extent *e,
                                    unsigned nr_replicas, struct open_bucket *ob,
                                    unsigned sectors)
{
        struct bch_extent_ptr tmp;
        bool has_data = false;
        unsigned i;

        /*
         * We're keeping any existing pointer k has, and appending new pointers:
         * __bch2_write() will only write to the pointers we add here:
         */

        BUG_ON(sectors > ob->sectors_free);

        /* didn't use all the ptrs: */
        if (nr_replicas < ob->nr_ptrs)
                has_data = true;

        for (i = 0; i < min(ob->nr_ptrs, nr_replicas); i++) {
                EBUG_ON(bch2_extent_has_device(extent_i_to_s_c(e), ob->ptrs[i].dev));

                tmp = ob->ptrs[i];
                tmp.cached = bkey_extent_is_cached(&e->k);
                tmp.offset += ob->ptr_offset[i];
                extent_ptr_append(e, tmp);

                ob->ptr_offset[i] += sectors;

                this_cpu_add(*c->devs[tmp.dev]->sectors_written, 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_bucket *ob)
{
        bool has_data = false;
        unsigned i;

        for (i = 0; i < ob->nr_ptrs; i++) {
                if (!ob_ptr_sectors_free(c, ob, &ob->ptrs[i]))
                        ob->has_full_ptrs = true;
                else
                        has_data = true;
        }

        if (likely(has_data))
                atomic_inc(&ob->pin);
        else
                BUG_ON(xchg(&wp->b, NULL) != ob);

        mutex_unlock(&ob->lock);
}

/*
 * Allocates some space in the cache to write to, and k to point to the newly
 * allocated space, and updates k->size and k->offset (to point to the
 * end of the newly allocated space).
 *
 * May allocate fewer sectors than @sectors, k->size indicates how many
 * sectors were actually allocated.
 *
 * Return codes:
 * - -EAGAIN: closure was added to waitlist
 * - -ENOSPC: out of space and no closure provided
 *
 * @c  - filesystem.
 * @wp - write point to use for allocating sectors.
 * @k  - key to return the allocated space information.
 * @cl - closure to wait for a bucket
 */
struct open_bucket *bch2_alloc_sectors(struct bch_fs *c,
                                       struct write_point *wp,
                                       struct bkey_i_extent *e,
                                       unsigned nr_replicas,
                                       unsigned nr_replicas_required,
                                       enum alloc_reserve reserve,
                                       struct closure *cl)
{
        struct open_bucket *ob;

        ob = bch2_alloc_sectors_start(c, wp, nr_replicas,
                                     nr_replicas_required,
                                     reserve, cl);
        if (IS_ERR_OR_NULL(ob))
                return ob;

        if (e->k.size > ob->sectors_free)
                bch2_key_resize(&e->k, ob->sectors_free);

        bch2_alloc_sectors_append_ptrs(c, e, nr_replicas, ob, e->k.size);

        bch2_alloc_sectors_done(c, wp, ob);

        return ob;
}

/* Startup/shutdown (ro/rw): */

void bch2_recalc_capacity(struct bch_fs *c)
{
        struct bch_tier *fastest_tier = NULL, *slowest_tier = NULL, *tier;
        struct bch_dev *ca;
        u64 total_capacity, capacity = 0, reserved_sectors = 0;
        unsigned long ra_pages = 0;
        unsigned i, j;

        for_each_online_member(ca, c, i) {
                struct backing_dev_info *bdi = ca->disk_sb.bdev->bd_bdi;

                ra_pages += bdi->ra_pages;
        }

        c->bdi.ra_pages = ra_pages;

        /* Find fastest, slowest tiers with devices: */

        for (tier = c->tiers;
             tier < c->tiers + ARRAY_SIZE(c->tiers); tier++) {
                if (!tier->devs.nr)
                        continue;
                if (!fastest_tier)
                        fastest_tier = tier;
                slowest_tier = tier;
        }

        c->fastest_tier = fastest_tier != slowest_tier ? fastest_tier : NULL;

        c->promote_write_point.group = &fastest_tier->devs;

        if (!fastest_tier)
                goto set_capacity;

        /*
         * Capacity of the filesystem is the capacity of all the devices in the
         * slowest (highest) tier - we don't include lower tier devices.
         */
        spin_lock(&slowest_tier->devs.lock);
        group_for_each_dev(ca, &slowest_tier->devs, i) {
                size_t reserve = 0;

                /*
                 * We need to reserve buckets (from the number
                 * of currently available buckets) against
                 * foreground writes so that mainly copygc can
                 * make forward progress.
                 *
                 * We need enough to refill the various reserves
                 * from scratch - copygc will use its entire
                 * reserve all at once, then run against when
                 * its reserve is refilled (from the formerly
                 * available buckets).
                 *
                 * This reserve is just used when considering if
                 * allocations for foreground writes must wait -
                 * not -ENOSPC calculations.
                 */
                for (j = 0; j < RESERVE_NONE; j++)
                        reserve += ca->free[j].size;

                reserve += ca->free_inc.size;

                reserve += ARRAY_SIZE(c->write_points);

                if (ca->mi.tier)
                        reserve += 1;   /* tiering write point */
                reserve += 1;           /* btree write point */

                reserved_sectors += reserve << ca->bucket_bits;

                capacity += (ca->mi.nbuckets -
                             ca->mi.first_bucket) <<
                        ca->bucket_bits;
        }
        spin_unlock(&slowest_tier->devs.lock);
set_capacity:
        total_capacity = capacity;

        capacity *= (100 - c->opts.gc_reserve_percent);
        capacity = div64_u64(capacity, 100);

        BUG_ON(reserved_sectors > total_capacity);

        capacity = min(capacity, total_capacity - reserved_sectors);

        c->capacity = capacity;

        if (c->capacity) {
                bch2_io_timer_add(&c->io_clock[READ],
                                 &c->prio_clock[READ].rescale);
                bch2_io_timer_add(&c->io_clock[WRITE],
                                 &c->prio_clock[WRITE].rescale);
        } else {
                bch2_io_timer_del(&c->io_clock[READ],
                                 &c->prio_clock[READ].rescale);
                bch2_io_timer_del(&c->io_clock[WRITE],
                                 &c->prio_clock[WRITE].rescale);
        }

        /* Wake up case someone was waiting for buckets */
        closure_wake_up(&c->freelist_wait);
}

static void bch2_stop_write_point(struct bch_fs *c, struct bch_dev *ca,
                                  struct write_point *wp)
{
        struct open_bucket *ob;
        struct bch_extent_ptr *ptr;

        ob = lock_writepoint(c, wp);
        if (!ob)
                return;

        for (ptr = ob->ptrs; ptr < ob->ptrs + ob->nr_ptrs; ptr++)
                if (ptr->dev == ca->dev_idx)
                        goto found;

        mutex_unlock(&ob->lock);
        return;
found:
        BUG_ON(xchg(&wp->b, NULL) != ob);
        mutex_unlock(&ob->lock);

        /* Drop writepoint's ref: */
        bch2_open_bucket_put(c, ob);
}

static bool bch2_dev_has_open_write_point(struct bch_fs *c, struct bch_dev *ca)
{
        struct bch_extent_ptr *ptr;
        struct open_bucket *ob;

        for (ob = c->open_buckets;
             ob < c->open_buckets + ARRAY_SIZE(c->open_buckets);
             ob++)
                if (atomic_read(&ob->pin)) {
                        mutex_lock(&ob->lock);
                        for (ptr = ob->ptrs; ptr < ob->ptrs + ob->nr_ptrs; ptr++)
                                if (ptr->dev == ca->dev_idx) {
                                        mutex_unlock(&ob->lock);
                                        return true;
                                }
                        mutex_unlock(&ob->lock);
                }

        return false;
}

/* device goes ro: */
void bch2_dev_allocator_remove(struct bch_fs *c, struct bch_dev *ca)
{
        struct dev_group *tier = &c->tiers[ca->mi.tier].devs;
        struct closure cl;
        unsigned i;

        BUG_ON(ca->alloc_thread);

        closure_init_stack(&cl);

        /* First, remove device from allocation groups: */

        bch2_dev_group_remove(&c->journal.devs, ca);
        bch2_dev_group_remove(tier, ca);
        bch2_dev_group_remove(&c->all_devs, ca);

        /*
         * Capacity is calculated based off of devices in allocation groups:
         */
        bch2_recalc_capacity(c);

        /* Next, close write points that point to this device... */
        for (i = 0; i < ARRAY_SIZE(c->write_points); i++)
                bch2_stop_write_point(c, ca, &c->write_points[i]);

        bch2_stop_write_point(c, ca, &ca->copygc_write_point);
        bch2_stop_write_point(c, ca, &c->promote_write_point);
        bch2_stop_write_point(c, ca, &ca->tiering_write_point);
        bch2_stop_write_point(c, ca, &c->migration_write_point);
        bch2_stop_write_point(c, ca, &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_bucket_put(c, a->ob);
        }
        mutex_unlock(&c->btree_reserve_cache_lock);

        /*
         * Wake up threads that were blocked on allocation, so they can notice
         * the device can no longer be removed and the capacity has changed:
         */
        closure_wake_up(&c->freelist_wait);

        /*
         * journal_res_get() can block waiting for free space in the journal -
         * it needs to notice there may not be devices to allocate from anymore:
         */
        wake_up(&c->journal.wait);

        /* Now wait for any in flight writes: */

        while (1) {
                closure_wait(&c->open_buckets_wait, &cl);

                if (!bch2_dev_has_open_write_point(c, ca)) {
                        closure_wake_up(&c->open_buckets_wait);
                        break;
                }

                closure_sync(&cl);
        }
}

/* device goes rw: */
void bch2_dev_allocator_add(struct bch_fs *c, struct bch_dev *ca)
{
        struct dev_group *tier = &c->tiers[ca->mi.tier].devs;
        struct bch_sb_field_journal *journal_buckets;
        bool has_journal;

        bch2_dev_group_add(&c->all_devs, ca);
        bch2_dev_group_add(tier, ca);

        mutex_lock(&c->sb_lock);
        journal_buckets = bch2_sb_get_journal(ca->disk_sb.sb);
        has_journal = bch2_nr_journal_buckets(journal_buckets) >=
                BCH_JOURNAL_BUCKETS_MIN;
        mutex_unlock(&c->sb_lock);

        if (has_journal)
                bch2_dev_group_add(&c->journal.devs, ca);
}

/* stop allocator thread: */
void bch2_dev_allocator_stop(struct bch_dev *ca)
{
        struct task_struct *p = ca->alloc_thread;

        ca->alloc_thread = NULL;
        smp_wmb();

        /*
         * We need an rcu barrier between setting ca->alloc_thread = NULL and
         * the thread shutting down to avoid a race with bch2_usage_update() -
         * the allocator thread itself does a synchronize_rcu() on exit.
         *
         * XXX: it would be better to have the rcu barrier be asynchronous
         * instead of blocking us here
         */
        if (p)
                kthread_stop(p);
}

/* start allocator thread: */
int bch2_dev_allocator_start(struct bch_dev *ca)
{
        struct task_struct *p;

        /*
         * allocator thread already started?
         */
        if (ca->alloc_thread)
                return 0;

        p = kthread_run(bch2_allocator_thread, ca, "bcache_allocator");
        if (IS_ERR(p))
                return PTR_ERR(p);

        ca->alloc_thread = p;
        return 0;
}

void bch2_fs_allocator_init(struct bch_fs *c)
{
        unsigned i;

        INIT_LIST_HEAD(&c->open_buckets_open);
        INIT_LIST_HEAD(&c->open_buckets_free);
        spin_lock_init(&c->open_buckets_lock);
        bch2_prio_timer_init(c, READ);
        bch2_prio_timer_init(c, WRITE);

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

        for (i = 1; i < ARRAY_SIZE(c->open_buckets); i++) {
                mutex_init(&c->open_buckets[i].lock);
                c->open_buckets_nr_free++;
                list_add(&c->open_buckets[i].list, &c->open_buckets_free);
        }

        spin_lock_init(&c->all_devs.lock);

        for (i = 0; i < ARRAY_SIZE(c->tiers); i++)
                spin_lock_init(&c->tiers[i].devs.lock);

        for (i = 0; i < ARRAY_SIZE(c->write_points); i++)
                c->write_points[i].throttle = true;

        c->pd_controllers_update_seconds = 5;
        INIT_DELAYED_WORK(&c->pd_controllers_update, pd_controllers_update);

        spin_lock_init(&c->foreground_write_pd_lock);
        bch2_pd_controller_init(&c->foreground_write_pd);
        /*
         * We do not want the write rate to have an effect on the computed
         * rate, for two reasons:
         *
         * We do not call bch2_ratelimit_delay() at all if the write rate
         * exceeds 1GB/s. In this case, the PD controller will think we are
         * not "keeping up" and not change the rate.
         */
        c->foreground_write_pd.backpressure = 0;
        init_timer(&c->foreground_write_wakeup);

        c->foreground_write_wakeup.data = (unsigned long) c;
        c->foreground_write_wakeup.function = bch2_wake_delayed_writes;
}