[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_cache.h"
#include "btree_io.h"
#include "btree_update.h"
#include "btree_gc.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/rculist.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_fs *, struct bch_dev *, int);

/* 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 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);

                for_each_member_device_rcu(ca, c, iter, &c->tiers[i].devs) {
                        struct bch_dev_usage stats = bch2_dev_usage_read(c, ca);

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

                        fragmented = max(0LL, fragmented);

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

                        faster_tiers_size               += size;
                        faster_tiers_dirty              += dirty;

                        copygc_can_free                 += fragmented;
                }
        }

        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;

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

/* Persistent alloc info: */

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 = bch_dev_bkey_exists(c, a.k->p.inode);

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

        lg_local_lock(&c->usage_lock);

        g = bucket(ca, 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);

        lg_local_unlock(&c->usage_lock);
}

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;
        struct bch_dev *ca;
        unsigned i;
        int ret;

        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));
        }

        mutex_lock(&c->prio_clock[READ].lock);
        for_each_member_device(ca, c, i) {
                down_read(&ca->bucket_lock);
                bch2_recalc_min_prio(c, ca, READ);
                up_read(&ca->bucket_lock);
        }
        mutex_unlock(&c->prio_clock[READ].lock);

        mutex_lock(&c->prio_clock[WRITE].lock);
        for_each_member_device(ca, c, i) {
                down_read(&ca->bucket_lock);
                bch2_recalc_min_prio(c, ca, WRITE);
                up_read(&ca->bucket_lock);
        }
        mutex_unlock(&c->prio_clock[WRITE].lock);

        return 0;
}

static int __bch2_alloc_write_key(struct bch_fs *c, struct bch_dev *ca,
                                  size_t b, 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 bucket *g;
        struct bkey_i_alloc *a;
        u8 *d;
        int ret;

        bch2_btree_iter_set_pos(iter, POS(ca->dev_idx, b));

        do {
                ret = btree_iter_err(bch2_btree_iter_peek_slot(iter));
                if (ret)
                        break;

                lg_local_lock(&c->usage_lock);
                g = bucket(ca, b);

                /* 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]);
                lg_local_unlock(&c->usage_lock);

                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 btree_iter iter;
        int ret;

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

        ca = bch_dev_bkey_exists(c, pos.inode);

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

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

        ret = __bch2_alloc_write_key(c, ca, pos.offset, &iter, NULL);
        bch2_btree_iter_unlock(&iter);
        return ret;
}

int bch2_alloc_write(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;
        int ret = 0;

        for_each_rw_member(ca, c, i) {
                struct btree_iter iter;
                unsigned long bucket;

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

                down_read(&ca->bucket_lock);
                for_each_set_bit(bucket, ca->buckets_dirty, ca->mi.nbuckets) {
                        ret = __bch2_alloc_write_key(c, ca, bucket, &iter, NULL);
                        if (ret)
                                break;

                        clear_bit(bucket, ca->buckets_dirty);
                }
                up_read(&ca->bucket_lock);
                bch2_btree_iter_unlock(&iter);

                if (ret) {
                        percpu_ref_put(&ca->io_ref);
                        break;
                }
        }

        return ret;
}

/* Bucket IO clocks: */

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

        lockdep_assert_held(&c->prio_clock[rw].lock);

        /* Determine min prio for this particular device */
        for_each_bucket(g, buckets)
                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 device, 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 bucket_array *buckets;
        struct bch_dev *ca;
        struct bucket *g;
        unsigned i;

        trace_rescale_prios(c);

        for_each_member_device(ca, c, i) {
                down_read(&ca->bucket_lock);
                buckets = bucket_array(ca);

                for_each_bucket(g, buckets)
                        g->prio[rw] = clock->hand -
                        (clock->hand - g->prio[rw]) / 2;

                bch2_recalc_min_prio(c, ca, rw);

                up_read(&ca->bucket_lock);
        }
}

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(&clock->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(&clock->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];

        clock->hand             = 1;
        clock->rw               = rw;
        clock->rescale.fn       = bch2_inc_clock_hand;
        clock->rescale.expire   = c->capacity >> 10;
        mutex_init(&clock->lock);
}

/* Background allocator 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 void verify_not_on_freelist(struct bch_fs *c, struct bch_dev *ca,
                                   size_t bucket)
{
        if (expensive_debug_checks(c) &&
            test_bit(BCH_FS_ALLOCATOR_STARTED, &c->flags)) {
                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);
        }
}

#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(c, 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 bool bch2_can_invalidate_bucket(struct bch_dev *ca,
                                       size_t bucket,
                                       struct bucket_mark mark)
{
        u8 gc_gen;

        if (!is_available_bucket(mark))
                return false;

        gc_gen = bucket_gc_gen(ca, bucket);

        if (gc_gen >= BUCKET_GC_GEN_MAX / 2)
                ca->inc_gen_needs_gc++;

        if (gc_gen >= BUCKET_GC_GEN_MAX)
                ca->inc_gen_really_needs_gc++;

        return gc_gen < BUCKET_GC_GEN_MAX;
}

static void bch2_invalidate_one_bucket(struct bch_fs *c, struct bch_dev *ca,
                                       size_t bucket)
{
        struct bucket_mark m;

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

        verify_not_on_freelist(c, ca, bucket);
        BUG_ON(!fifo_push(&ca->free_inc, bucket));
        spin_unlock(&c->freelist_lock);

        /* gc lock held: */
        bucket_io_clock_reset(c, ca, bucket, READ);
        bucket_io_clock_reset(c, ca, bucket, WRITE);

        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_fs *c, struct bch_dev *ca,
                                     size_t b, struct bucket_mark m)
{
        /*
         * Time since last read, scaled to [0, 8) where larger value indicates
         * more recently read data:
         */
        unsigned long hotness =
                (bucket(ca, b)->prio[READ]      - ca->min_prio[READ]) * 7 /
                (c->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, c->journal.last_seq_ondisk);

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

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 find_reclaimable_buckets_lru(struct bch_fs *c, struct bch_dev *ca)
{
        struct bucket_array *buckets;
        struct alloc_heap_entry e;
        size_t b;

        ca->alloc_heap.used = 0;

        mutex_lock(&c->prio_clock[READ].lock);
        down_read(&ca->bucket_lock);

        buckets = bucket_array(ca);

        bch2_recalc_min_prio(c, ca, READ);

        /*
         * 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 (b = ca->mi.first_bucket; b < ca->mi.nbuckets; b++) {
                struct bucket_mark m = READ_ONCE(buckets->b[b].mark);

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

                e = (struct alloc_heap_entry) {
                        .bucket = b,
                        .key    = bucket_sort_key(c, ca, b, m)
                };

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

        up_read(&ca->bucket_lock);
        mutex_unlock(&c->prio_clock[READ].lock);

        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(c, ca, e.bucket);
}

static void find_reclaimable_buckets_fifo(struct bch_fs *c, struct bch_dev *ca)
{
        struct bucket_array *buckets = bucket_array(ca);
        struct bucket_mark m;
        size_t b, checked;

        for (checked = 0;
             checked < ca->mi.nbuckets && !fifo_full(&ca->free_inc);
             checked++) {
                if (ca->fifo_last_bucket <  ca->mi.first_bucket ||
                    ca->fifo_last_bucket >= ca->mi.nbuckets)
                        ca->fifo_last_bucket = ca->mi.first_bucket;

                b = ca->fifo_last_bucket++;

                m = READ_ONCE(buckets->b[b].mark);

                if (bch2_can_invalidate_bucket(ca, b, m))
                        bch2_invalidate_one_bucket(c, ca, b);
        }
}

static void find_reclaimable_buckets_random(struct bch_fs *c, struct bch_dev *ca)
{
        struct bucket_array *buckets = bucket_array(ca);
        struct bucket_mark m;
        size_t checked;

        for (checked = 0;
             checked < ca->mi.nbuckets / 2 && !fifo_full(&ca->free_inc);
             checked++) {
                size_t b = bch2_rand_range(ca->mi.nbuckets -
                                           ca->mi.first_bucket) +
                        ca->mi.first_bucket;

                m = READ_ONCE(buckets->b[b].mark);

                if (bch2_can_invalidate_bucket(ca, b, m))
                        bch2_invalidate_one_bucket(c, ca, b);
        }
}

static void find_reclaimable_buckets(struct bch_fs *c, 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:
                find_reclaimable_buckets_lru(c, ca);
                break;
        case CACHE_REPLACEMENT_FIFO:
                find_reclaimable_buckets_fifo(c, ca);
                break;
        case CACHE_REPLACEMENT_RANDOM:
                find_reclaimable_buckets_random(c, 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 void sort_free_inc(struct bch_fs *c, struct bch_dev *ca)
{
        BUG_ON(ca->free_inc.front);

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

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

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

        /*
         * XXX: if ca->nr_invalidated != 0, just return if we'd block doing the
         * btree update or journal_res_get
         */
        while (ca->nr_invalidated < min(nr, fifo_used(&ca->free_inc))) {
                size_t b = fifo_idx_entry(&ca->free_inc, ca->nr_invalidated);

                ret = __bch2_alloc_write_key(c, ca, b, &iter, journal_seq);
                if (ret)
                        break;

                ca->nr_invalidated++;
        }

        bch2_btree_iter_unlock(&iter);
        return ret;
}

static bool __push_invalidated_bucket(struct bch_fs *c, struct bch_dev *ca, size_t bucket)
{
        unsigned i;

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

        return false;
}

static int push_invalidated_bucket(struct bch_fs *c, struct bch_dev *ca, size_t bucket)
{
        int ret = 0;

        while (1) {
                set_current_state(TASK_INTERRUPTIBLE);

                if (__push_invalidated_bucket(c, ca, bucket))
                        break;

                if ((current->flags & PF_KTHREAD) &&
                    kthread_should_stop()) {
                        ret = -1;
                        break;
                }

                schedule();
                try_to_freeze();
        }

        __set_current_state(TASK_RUNNING);
        return 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 int discard_invalidated_buckets(struct bch_fs *c, struct bch_dev *ca)
{
        while (ca->nr_invalidated) {
                size_t bucket = fifo_peek(&ca->free_inc);

                BUG_ON(fifo_empty(&ca->free_inc) || !ca->nr_invalidated);

                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);

                if (push_invalidated_bucket(c, ca, bucket))
                        return -1;
        }

        return 0;
}

/**
 * bch_allocator_thread - move buckets from free_inc to reserves
 *
 * The free_inc FIFO is populated by find_reclaimable_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;
        int ret;

        set_freezable();

        while (1) {
                while (1) {
                        ret = discard_invalidated_buckets(c, ca);
                        if (ret)
                                return 0;

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

                        journal_seq = 0;
                        ret = bch2_invalidate_free_inc(c, ca, &journal_seq, SIZE_MAX);
                        if (ret)
                                return 0;

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

                        /*
                         * journal error - buckets haven't actually been
                         * invalidated, can't discard them:
                         */
                        if (ret)
                                return 0;
                }

                /* 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);
                        return 0;
                }

                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
                         */

                        find_reclaimable_buckets(c, 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);
                                return 0;
                        }
                }
                up_read(&c->gc_lock);

                sort_free_inc(c, ca);

                /*
                 * free_inc is now full of newly-invalidated buckets: next,
                 * write out the new bucket gens:
                 */
        }
}

/* Allocation */

/*
 * 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);

        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);

        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);
}

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;
}

/* _only_ for allocating the journal and btree roots on a brand new fs: */
int bch2_bucket_alloc_startup(struct bch_fs *c, 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)) {
                        bch2_mark_alloc_bucket(c, ca, b, true,
                                        gc_pos_alloc(c, NULL),
                                        BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
                                        BCH_BUCKET_MARK_GC_LOCK_HELD);
                        set_bit(b, ca->buckets_dirty);
                        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
 * */
int 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;

        spin_lock(&c->freelist_lock);
        if (may_alloc_partial &&
            ca->open_buckets_partial_nr) {
                int ret = ca->open_buckets_partial[--ca->open_buckets_partial_nr];
                c->open_buckets[ret].on_partial_list = false;
                spin_unlock(&c->freelist_lock);
                return ret;
        }

        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 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 (unlikely(test_bit(BCH_FS_BRAND_NEW_FS, &c->flags)) &&
            (bucket = bch2_bucket_alloc_startup(c, ca)) >= 0)
                goto out;

        spin_unlock(&c->freelist_lock);

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

        ob = bch2_open_bucket_alloc(c);

        spin_lock(&ob->lock);
        lg_local_lock(&c->usage_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);

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

        spin_unlock(&c->freelist_lock);

        bch2_wake_allocator(ca);

        trace_bucket_alloc(ca, reserve);
        return ob - c->open_buckets;
}

struct dev_alloc_list bch2_wp_alloc_list(struct bch_fs *c,
                                         struct write_point *wp,
                                         struct bch_devs_mask *devs)
{
        struct dev_alloc_list ret = { .nr = 0 };
        struct bch_dev *ca, *ca2;
        unsigned i, j;

        for_each_member_device_rcu(ca, c, i, devs) {
                for (j = 0; j < ret.nr; j++) {
                        unsigned idx = ret.devs[j];

                        ca2 = rcu_dereference(c->devs[idx]);
                        if (!ca2)
                                break;

                        if (ca->mi.tier < ca2->mi.tier)
                                break;

                        if (ca->mi.tier == ca2->mi.tier &&
                            wp->next_alloc[i] < wp->next_alloc[idx])
                                break;
                }

                array_insert_item(ret.devs, ret.nr, j, i);
        }

        return ret;
}

void bch2_wp_rescale(struct bch_fs *c, struct bch_dev *ca,
                     struct write_point *wp)
{
        unsigned i;

        for (i = 0; i < ARRAY_SIZE(wp->next_alloc); i++)
                wp->next_alloc[i] >>= 1;
}

static enum bucket_alloc_ret __bch2_bucket_alloc_set(struct bch_fs *c,
                                        struct write_point *wp,
                                        unsigned nr_replicas,
                                        enum alloc_reserve reserve,
                                        struct bch_devs_mask *devs,
                                        struct closure *cl)
{
        enum bucket_alloc_ret ret = NO_DEVICES;
        struct dev_alloc_list devs_sorted;
        u64 buckets_free;
        unsigned i;

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

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

        rcu_read_lock();
        devs_sorted = bch2_wp_alloc_list(c, wp, devs);

        for (i = 0; i < devs_sorted.nr; i++) {
                struct bch_dev *ca =
                        rcu_dereference(c->devs[devs_sorted.devs[i]]);
                int ob;

                if (!ca)
                        continue;

                ob = bch2_bucket_alloc(c, ca, reserve,
                                       wp->type == BCH_DATA_USER, cl);
                if (ob < 0) {
                        ret = ob;
                        if (ret == OPEN_BUCKETS_EMPTY)
                                break;
                        continue;
                }

                BUG_ON(ob <= 0 || ob > U8_MAX);
                BUG_ON(wp->nr_ptrs >= ARRAY_SIZE(wp->ptrs));
                wp->ptrs[wp->nr_ptrs++] = c->open_buckets + ob;

                buckets_free = U64_MAX, dev_buckets_free(c, ca);
                if (buckets_free)
                        wp->next_alloc[ca->dev_idx] +=
                                div64_u64(U64_MAX, buckets_free *
                                          ca->mi.bucket_size);
                else
                        wp->next_alloc[ca->dev_idx] = U64_MAX;
                bch2_wp_rescale(c, ca, wp);

                __clear_bit(ca->dev_idx, devs->d);

                if (wp->nr_ptrs == nr_replicas) {
                        ret = ALLOC_SUCCESS;
                        break;
                }
        }

        EBUG_ON(reserve == RESERVE_MOVINGGC &&
                ret != ALLOC_SUCCESS &&
                ret != OPEN_BUCKETS_EMPTY);
        rcu_read_unlock();
        return ret;
}

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

        while (1) {
                switch (__bch2_bucket_alloc_set(c, wp, nr_replicas,
                                                reserve, devs, cl)) {
                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)
                                return -ENOSPC;

                        if (waiting)
                                return -EAGAIN;

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

/* Sector allocator */

static void writepoint_drop_ptrs(struct bch_fs *c,
                                 struct write_point *wp,
                                 struct bch_devs_mask *devs,
                                 unsigned nr_ptrs_dislike)
{
        int i;

        if (!nr_ptrs_dislike)
                return;

        for (i = wp->nr_ptrs - 1; i >= 0; --i) {
                struct open_bucket *ob = wp->ptrs[i];
                struct bch_dev *ca = bch_dev_bkey_exists(c, ob->ptr.dev);

                if (nr_ptrs_dislike && !test_bit(ob->ptr.dev, devs->d)) {
                        BUG_ON(ca->open_buckets_partial_nr >=
                               ARRAY_SIZE(ca->open_buckets_partial));

                        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);

                        array_remove_item(wp->ptrs, wp->nr_ptrs, i);
                        --nr_ptrs_dislike;
                }
        }
}

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

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

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

static int open_bucket_add_buckets(struct bch_fs *c,
                                   struct bch_devs_mask *_devs,
                                   struct write_point *wp,
                                   struct bch_devs_list *devs_have,
                                   unsigned nr_replicas,
                                   enum alloc_reserve reserve,
                                   struct closure *cl)
{
        struct bch_devs_mask devs = c->rw_devs[wp->type];
        struct open_bucket *ob;
        unsigned i;

        if (wp->nr_ptrs >= nr_replicas)
                return 0;

        /* 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);

        writepoint_for_each_ptr(wp, ob, i)
                __clear_bit(ob->ptr.dev, devs.d);

        if (_devs)
                bitmap_and(devs.d, devs.d, _devs->d, BCH_SB_MEMBERS_MAX);

        return bch2_bucket_alloc_set(c, wp, nr_replicas, reserve, &devs, cl);
}

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 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 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;
        }

        oldest = NULL;
        for (wp = c->write_points;
             wp < c->write_points + ARRAY_SIZE(c->write_points);
             wp++)
                if (!oldest || time_before64(wp->last_used, oldest->last_used))
                        oldest = wp;

        mutex_lock(&oldest->lock);
        mutex_lock(&c->write_points_hash_lock);
        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,
                                struct bch_devs_mask *devs,
                                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 i, nr_ptrs_dislike = 0, nr_ptrs_have = 0;
        int ret;

        BUG_ON(!nr_replicas || !nr_replicas_required);

        wp = writepoint_find(c, write_point.v);

        /* does ob have ptrs we don't need? */
        writepoint_for_each_ptr(wp, ob, i)
                if (bch2_dev_list_has_dev(*devs_have, ob->ptr.dev))
                        nr_ptrs_have++;
                else if (devs && !test_bit(ob->ptr.dev, devs->d))
                        nr_ptrs_dislike++;

        ret = open_bucket_add_buckets(c, devs, wp, devs_have,
                                nr_replicas + nr_ptrs_have + nr_ptrs_dislike,
                                reserve, cl);
        if (ret && ret != -EROFS)
                goto err;

        if (wp->nr_ptrs <
            nr_ptrs_have + nr_ptrs_dislike + nr_replicas_required) {
                ret = -EROFS;
                goto err;
        }

        if ((int) wp->nr_ptrs - nr_ptrs_dislike < nr_replicas)
                nr_ptrs_dislike = clamp_t(int, wp->nr_ptrs - nr_replicas,
                                          0, nr_ptrs_dislike);

        /* Remove pointers we don't want to use: */
        writepoint_drop_ptrs(c, wp, devs, nr_ptrs_dislike);

        /*
         * Move pointers to devices we already have to end of open bucket
         * pointer list - note that removing pointers we don't want to use might
         * have changed nr_ptrs_have:
         */
        if (nr_ptrs_have) {
                i = nr_ptrs_have = 0;
                while (i < wp->nr_ptrs - nr_ptrs_have)
                        if (bch2_dev_list_has_dev(*devs_have, wp->ptrs[i]->ptr.dev)) {
                                nr_ptrs_have++;
                                swap(wp->ptrs[i], wp->ptrs[wp->nr_ptrs - nr_ptrs_have]);
                        } else {
                                i++;
                        }
        }

        wp->nr_ptrs_can_use =
                min_t(unsigned, nr_replicas, wp->nr_ptrs - nr_ptrs_have);

        BUG_ON(wp->nr_ptrs_can_use < nr_replicas_required ||
               wp->nr_ptrs_can_use > wp->nr_ptrs);

        wp->sectors_free = UINT_MAX;

        for (i = 0; i < wp->nr_ptrs_can_use; i++)
                wp->sectors_free = min(wp->sectors_free,
                                       wp->ptrs[i]->sectors_free);

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

        verify_not_stale(c, wp);

        return wp;
err:
        mutex_unlock(&wp->lock);
        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)
{
        unsigned i;

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

        for (i = 0; i < wp->nr_ptrs_can_use; i++) {
                struct open_bucket *ob = wp->ptrs[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);
                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)
{
        int i;

        for (i = wp->nr_ptrs - 1; i >= 0; --i) {
                struct open_bucket *ob = wp->ptrs[i];

                if (!ob->sectors_free) {
                        array_remove_item(wp->ptrs, wp->nr_ptrs, i);
                        bch2_open_bucket_put(c, ob);
                }
        }

        mutex_unlock(&wp->lock);
}

/* 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;

        lockdep_assert_held(&c->state_lock);

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

                ra_pages += bdi->ra_pages;
        }

        bch2_set_ra_pages(c, ra_pages);

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

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

        c->fastest_tier = fastest_tier != slowest_tier ? fastest_tier : NULL;
        c->fastest_devs = fastest_tier != slowest_tier ? &fastest_tier->devs : NULL;

        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.
         */
        for_each_member_device_rcu(ca, c, i, &slowest_tier->devs) {
                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 += bucket_to_sector(ca, reserve);

                capacity += bucket_to_sector(ca, ca->mi.nbuckets -
                                             ca->mi.first_bucket);
        }
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 bch_devs_mask not_self;

        bitmap_complement(not_self.d, ca->self.d, BCH_SB_MEMBERS_MAX);

        mutex_lock(&wp->lock);
        writepoint_drop_ptrs(c, wp, &not_self, wp->nr_ptrs);
        mutex_unlock(&wp->lock);
}

static bool bch2_dev_has_open_write_point(struct bch_fs *c, struct bch_dev *ca)
{
        struct open_bucket *ob;
        bool ret = false;

        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 &&
                    ob->ptr.dev == ca->dev_idx)
                        ret = true;
                spin_unlock(&ob->lock);
        }

        return ret;
}

/* device goes ro: */
void bch2_dev_allocator_remove(struct bch_fs *c, struct bch_dev *ca)
{
        unsigned i;

        BUG_ON(ca->alloc_thread);

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

        clear_bit(ca->dev_idx, c->tiers[ca->mi.tier].devs.d);
        for (i = 0; i < ARRAY_SIZE(c->rw_devs); i++)
                clear_bit(ca->dev_idx, c->rw_devs[i].d);

        /*
         * 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->tiers[ca->mi.tier].wp);
        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_refs(c, &a->ob.nr, a->ob.refs);
        }
        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: */

        closure_wait_event(&c->open_buckets_wait,
                           !bch2_dev_has_open_write_point(c, ca));
}

/* device goes rw: */
void bch2_dev_allocator_add(struct bch_fs *c, struct bch_dev *ca)
{
        unsigned i;

        for (i = 0; i < ARRAY_SIZE(c->rw_devs); i++)
                if (ca->mi.data_allowed & (1 << i))
                        set_bit(ca->dev_idx, c->rw_devs[i].d);
        set_bit(ca->dev_idx, c->tiers[ca->mi.tier].devs.d);
}

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

        ca->alloc_thread = NULL;

        /*
         * We need an rcu barrier between setting ca->alloc_thread = NULL and
         * the thread shutting down to avoid bch2_wake_allocator() racing:
         *
         * XXX: it would be better to have the rcu barrier be asynchronous
         * instead of blocking us here
         */
        synchronize_rcu();

        if (p) {
                kthread_stop(p);
                put_task_struct(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_create(bch2_allocator_thread, ca, "bcache_allocator");
        if (IS_ERR(p))
                return PTR_ERR(p);

        get_task_struct(p);
        ca->alloc_thread = p;
        wake_up_process(p);
        return 0;
}

static void allocator_start_issue_discards(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned dev_iter;
        size_t i, bu;

        for_each_rw_member(ca, c, dev_iter) {
                unsigned done = 0;

                fifo_for_each_entry(bu, &ca->free_inc, i) {
                        if (done == ca->nr_invalidated)
                                break;

                        blkdev_issue_discard(ca->disk_sb.bdev,
                                             bucket_to_sector(ca, bu),
                                             ca->mi.bucket_size, GFP_NOIO, 0);
                        done++;
                }
        }
}

static int __bch2_fs_allocator_start(struct bch_fs *c)
{
        struct bch_dev *ca;
        size_t bu, i, devs_have_enough = 0;
        unsigned dev_iter;
        u64 journal_seq = 0;
        bool invalidating_data = false;
        int ret = 0;

        if (test_bit(BCH_FS_GC_FAILURE, &c->flags))
                return -1;

        /* Scan for buckets that are already invalidated: */
        for_each_rw_member(ca, c, dev_iter) {
                struct btree_iter iter;
                struct bucket_mark m;
                struct bkey_s_c k;

                for_each_btree_key(&iter, c, BTREE_ID_ALLOC, POS(ca->dev_idx, 0), 0, k) {
                        if (k.k->type != BCH_ALLOC)
                                continue;

                        bu = k.k->p.offset;
                        m = READ_ONCE(bucket(ca, bu)->mark);

                        if (!is_available_bucket(m) || m.cached_sectors)
                                continue;

                        bch2_mark_alloc_bucket(c, ca, bu, true,
                                        gc_pos_alloc(c, NULL),
                                        BCH_BUCKET_MARK_MAY_MAKE_UNAVAILABLE|
                                        BCH_BUCKET_MARK_GC_LOCK_HELD);

                        fifo_push(&ca->free_inc, bu);
                        ca->nr_invalidated++;

                        if (fifo_full(&ca->free_inc))
                                break;
                }
                bch2_btree_iter_unlock(&iter);
        }

        /* did we find enough buckets? */
        for_each_rw_member(ca, c, dev_iter)
                devs_have_enough += (fifo_used(&ca->free_inc) >=
                                     ca->free[RESERVE_BTREE].size);

        if (devs_have_enough >= c->opts.metadata_replicas)
                return 0;

        /* clear out free_inc - find_reclaimable_buckets() assumes it's empty */
        for_each_rw_member(ca, c, dev_iter)
                discard_invalidated_buckets(c, ca);

        for_each_rw_member(ca, c, dev_iter) {
                BUG_ON(!fifo_empty(&ca->free_inc));
                ca->free_inc.front = ca->free_inc.back  = 0;

                find_reclaimable_buckets(c, ca);
                sort_free_inc(c, ca);

                invalidating_data |= ca->allocator_invalidating_data;

                fifo_for_each_entry(bu, &ca->free_inc, i)
                        if (!fifo_push(&ca->free[RESERVE_BTREE], bu))
                                break;
        }

        /*
         * We're moving buckets to freelists _before_ they've been marked as
         * invalidated on disk - we have to so that we can allocate new btree
         * nodes to mark them as invalidated on disk.
         *
         * However, we can't _write_ to any of these buckets yet - they might
         * have cached data in them, which is live until they're marked as
         * invalidated on disk:
         */
        if (invalidating_data)
                set_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags);
        else
                allocator_start_issue_discards(c);

        /*
         * XXX: it's possible for this to deadlock waiting on journal reclaim,
         * since we're holding btree writes. What then?
         */

        for_each_rw_member(ca, c, dev_iter) {
                ret = bch2_invalidate_free_inc(c, ca, &journal_seq,
                                               ca->free[RESERVE_BTREE].size);
                if (ret) {
                        percpu_ref_put(&ca->io_ref);
                        return ret;
                }
        }

        if (invalidating_data) {
                ret = bch2_journal_flush_seq(&c->journal, journal_seq);
                if (ret)
                        return ret;
        }

        if (invalidating_data)
                allocator_start_issue_discards(c);

        for_each_rw_member(ca, c, dev_iter)
                while (ca->nr_invalidated) {
                        BUG_ON(!fifo_pop(&ca->free_inc, bu));
                        ca->nr_invalidated--;
                }

        set_bit(BCH_FS_ALLOCATOR_STARTED, &c->flags);

        /* now flush dirty btree nodes: */
        if (invalidating_data) {
                struct bucket_table *tbl;
                struct rhash_head *pos;
                struct btree *b;

                clear_bit(BCH_FS_HOLD_BTREE_WRITES, &c->flags);
again:
                rcu_read_lock();
                for_each_cached_btree(b, c, tbl, i, pos)
                        if (btree_node_dirty(b) && (!b->written || b->level)) {
                                rcu_read_unlock();
                                six_lock_read(&b->lock);
                                bch2_btree_node_write(c, b, SIX_LOCK_read);
                                six_unlock_read(&b->lock);
                                goto again;
                        }
                rcu_read_unlock();
        }

        return 0;
}

int bch2_fs_allocator_start(struct bch_fs *c)
{
        struct bch_dev *ca;
        unsigned i;
        int ret;

        down_read(&c->gc_lock);
        ret = __bch2_fs_allocator_start(c);
        up_read(&c->gc_lock);

        if (ret)
                return ret;

        for_each_rw_member(ca, c, i) {
                ret = bch2_dev_allocator_start(ca);
                if (ret) {
                        percpu_ref_put(&ca->io_ref);
                        return ret;
                }
        }

        return bch2_alloc_write(c);
}

void bch2_fs_allocator_init(struct bch_fs *c)
{
        struct open_bucket *ob;
        struct write_point *wp;
        unsigned i;

        mutex_init(&c->write_points_hash_lock);
        spin_lock_init(&c->freelist_lock);
        bch2_prio_timer_init(c, READ);
        bch2_prio_timer_init(c, WRITE);

        /* 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);

        for (i = 0; i < ARRAY_SIZE(c->tiers); i++)
                writepoint_init(&c->tiers[i].wp, BCH_DATA_USER);

        for (wp = c->write_points;
             wp < c->write_points + ARRAY_SIZE(c->write_points); 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));
        }

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