/*
 * 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 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.
 *
 * There is another freelist, because sometimes we have buckets that we know
 * have nothing pointing into them - these we can reuse without waiting for
 * priorities to be rewritten. These come from freed btree nodes and buckets
 * that garbage collection discovered no longer had valid keys pointing into
 * them (because they were overwritten). That's the unused list - buckets on the
 * unused list move to the free list, optionally being discarded in the process.
 *
 * It's also 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.
 *
 * bch_bucket_alloc() allocates a single bucket from a specific cache.
 *
 * bch_bucket_alloc_set() allocates one or more buckets from different caches
 * out of a cache set.
 *
 * free_some_buckets() drives all the processes described above. It's called
 * from bch_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 "bcache.h"
#include "btree.h"

#include <linux/freezer.h>
#include <linux/kthread.h>
#include <linux/random.h>
#include <trace/events/bcache.h>

#define MAX_IN_FLIGHT_DISCARDS          8U

/* Bucket heap / gen */

uint8_t bch_inc_gen(struct cache *ca, struct bucket *b)
{
        uint8_t ret = ++b->gen;

        ca->set->need_gc = max(ca->set->need_gc, bucket_gc_gen(b));
        WARN_ON_ONCE(ca->set->need_gc > BUCKET_GC_GEN_MAX);

        if (CACHE_SYNC(&ca->set->sb)) {
                ca->need_save_prio = max(ca->need_save_prio,
                                         bucket_disk_gen(b));
                WARN_ON_ONCE(ca->need_save_prio > BUCKET_DISK_GEN_MAX);
        }

        return ret;
}

void bch_rescale_priorities(struct cache_set *c, int sectors)
{
        struct cache *ca;
        struct bucket *b;
        unsigned next = c->nbuckets * c->sb.bucket_size / 1024;
        unsigned i;
        int r;

        atomic_sub(sectors, &c->rescale);

        do {
                r = atomic_read(&c->rescale);

                if (r >= 0)
                        return;
        } while (atomic_cmpxchg(&c->rescale, r, r + next) != r);

        mutex_lock(&c->bucket_lock);

        c->min_prio = USHRT_MAX;

        for_each_cache(ca, c, i)
                for_each_bucket(b, ca)
                        if (b->prio &&
                            b->prio != BTREE_PRIO &&
                            !atomic_read(&b->pin)) {
                                b->prio--;
                                c->min_prio = min(c->min_prio, b->prio);
                        }

        mutex_unlock(&c->bucket_lock);
}

/* Discard/TRIM */

struct discard {
        struct list_head        list;
        struct work_struct      work;
        struct cache            *ca;
        long                    bucket;

        struct bio              bio;
        struct bio_vec          bv;
};

static void discard_finish(struct work_struct *w)
{
        struct discard *d = container_of(w, struct discard, work);
        struct cache *ca = d->ca;
        char buf[BDEVNAME_SIZE];

        if (!test_bit(BIO_UPTODATE, &d->bio.bi_flags)) {
                pr_notice("discard error on %s, disabling",
                         bdevname(ca->bdev, buf));
                d->ca->discard = 0;
        }

        mutex_lock(&ca->set->bucket_lock);

        fifo_push(&ca->free, d->bucket);
        list_add(&d->list, &ca->discards);
        atomic_dec(&ca->discards_in_flight);

        mutex_unlock(&ca->set->bucket_lock);

        closure_wake_up(&ca->set->bucket_wait);
        wake_up_process(ca->alloc_thread);

        closure_put(&ca->set->cl);
}

static void discard_endio(struct bio *bio, int error)
{
        struct discard *d = container_of(bio, struct discard, bio);
        schedule_work(&d->work);
}

static void do_discard(struct cache *ca, long bucket)
{
        struct discard *d = list_first_entry(&ca->discards,
                                             struct discard, list);

        list_del(&d->list);
        d->bucket = bucket;

        atomic_inc(&ca->discards_in_flight);
        closure_get(&ca->set->cl);

        bio_init(&d->bio);

        d->bio.bi_sector        = bucket_to_sector(ca->set, d->bucket);
        d->bio.bi_bdev          = ca->bdev;
        d->bio.bi_rw            = REQ_WRITE|REQ_DISCARD;
        d->bio.bi_max_vecs      = 1;
        d->bio.bi_io_vec        = d->bio.bi_inline_vecs;
        d->bio.bi_size          = bucket_bytes(ca);
        d->bio.bi_end_io        = discard_endio;
        bio_set_prio(&d->bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));

        submit_bio(0, &d->bio);
}

/* Allocation */

static inline bool can_inc_bucket_gen(struct bucket *b)
{
        return bucket_gc_gen(b) < BUCKET_GC_GEN_MAX &&
                bucket_disk_gen(b) < BUCKET_DISK_GEN_MAX;
}

bool bch_bucket_add_unused(struct cache *ca, struct bucket *b)
{
        BUG_ON(GC_MARK(b) || GC_SECTORS_USED(b));

        if (fifo_used(&ca->free) > ca->watermark[WATERMARK_MOVINGGC] &&
            CACHE_REPLACEMENT(&ca->sb) == CACHE_REPLACEMENT_FIFO)
                return false;

        b->prio = 0;

        if (can_inc_bucket_gen(b) &&
            fifo_push(&ca->unused, b - ca->buckets)) {
                atomic_inc(&b->pin);
                return true;
        }

        return false;
}

static bool can_invalidate_bucket(struct cache *ca, struct bucket *b)
{
        return GC_MARK(b) == GC_MARK_RECLAIMABLE &&
                !atomic_read(&b->pin) &&
                can_inc_bucket_gen(b);
}

static void invalidate_one_bucket(struct cache *ca, struct bucket *b)
{
        bch_inc_gen(ca, b);
        b->prio = INITIAL_PRIO;
        atomic_inc(&b->pin);
        fifo_push(&ca->free_inc, b - ca->buckets);
}

#define bucket_prio(b)                          \
        (((unsigned) (b->prio - ca->set->min_prio)) * GC_SECTORS_USED(b))

#define bucket_max_cmp(l, r)    (bucket_prio(l) < bucket_prio(r))
#define bucket_min_cmp(l, r)    (bucket_prio(l) > bucket_prio(r))

static void invalidate_buckets_lru(struct cache *ca)
{
        struct bucket *b;
        ssize_t i;

        ca->heap.used = 0;

        for_each_bucket(b, ca) {
                /*
                 * If we fill up the unused list, if we then return before
                 * adding anything to the free_inc list we'll skip writing
                 * prios/gens and just go back to allocating from the unused
                 * list:
                 */
                if (fifo_full(&ca->unused))
                        return;

                if (!can_invalidate_bucket(ca, b))
                        continue;

                if (!GC_SECTORS_USED(b) &&
                    bch_bucket_add_unused(ca, b))
                        continue;

                if (!heap_full(&ca->heap))
                        heap_add(&ca->heap, b, bucket_max_cmp);
                else if (bucket_max_cmp(b, heap_peek(&ca->heap))) {
                        ca->heap.data[0] = b;
                        heap_sift(&ca->heap, 0, bucket_max_cmp);
                }
        }

        for (i = ca->heap.used / 2 - 1; i >= 0; --i)
                heap_sift(&ca->heap, i, bucket_min_cmp);

        while (!fifo_full(&ca->free_inc)) {
                if (!heap_pop(&ca->heap, b, bucket_min_cmp)) {
                        /*
                         * We don't want to be calling invalidate_buckets()
                         * multiple times when it can't do anything
                         */
                        ca->invalidate_needs_gc = 1;
                        bch_queue_gc(ca->set);
                        return;
                }

                invalidate_one_bucket(ca, b);
        }
}

static void invalidate_buckets_fifo(struct cache *ca)
{
        struct bucket *b;
        size_t checked = 0;

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

                b = ca->buckets + ca->fifo_last_bucket++;

                if (can_invalidate_bucket(ca, b))
                        invalidate_one_bucket(ca, b);

                if (++checked >= ca->sb.nbuckets) {
                        ca->invalidate_needs_gc = 1;
                        bch_queue_gc(ca->set);
                        return;
                }
        }
}

static void invalidate_buckets_random(struct cache *ca)
{
        struct bucket *b;
        size_t checked = 0;

        while (!fifo_full(&ca->free_inc)) {
                size_t n;
                get_random_bytes(&n, sizeof(n));

                n %= (size_t) (ca->sb.nbuckets - ca->sb.first_bucket);
                n += ca->sb.first_bucket;

                b = ca->buckets + n;

                if (can_invalidate_bucket(ca, b))
                        invalidate_one_bucket(ca, b);

                if (++checked >= ca->sb.nbuckets / 2) {
                        ca->invalidate_needs_gc = 1;
                        bch_queue_gc(ca->set);
                        return;
                }
        }
}

static void invalidate_buckets(struct cache *ca)
{
        if (ca->invalidate_needs_gc)
                return;

        switch (CACHE_REPLACEMENT(&ca->sb)) {
        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;
        }

        trace_bcache_alloc_invalidate(ca);
}

#define allocator_wait(ca, cond)                                        \
do {                                                                    \
        while (1) {                                                     \
                set_current_state(TASK_INTERRUPTIBLE);                  \
                if (cond)                                               \
                        break;                                          \
                                                                        \
                mutex_unlock(&(ca)->set->bucket_lock);                  \
                if (kthread_should_stop())                              \
                        return 0;                                       \
                                                                        \
                try_to_freeze();                                        \
                schedule();                                             \
                mutex_lock(&(ca)->set->bucket_lock);                    \
        }                                                               \
        __set_current_state(TASK_RUNNING);                              \
} while (0)

static int bch_allocator_thread(void *arg)
{
        struct cache *ca = arg;

        mutex_lock(&ca->set->bucket_lock);

        while (1) {
                /*
                 * First, we pull buckets off of the unused and free_inc lists,
                 * possibly issue discards to them, then we add the bucket to
                 * the free list:
                 */
                while (1) {
                        long bucket;

                        if ((!atomic_read(&ca->set->prio_blocked) ||
                             !CACHE_SYNC(&ca->set->sb)) &&
                            !fifo_empty(&ca->unused))
                                fifo_pop(&ca->unused, bucket);
                        else if (!fifo_empty(&ca->free_inc))
                                fifo_pop(&ca->free_inc, bucket);
                        else
                                break;

                        allocator_wait(ca, (int) fifo_free(&ca->free) >
                                       atomic_read(&ca->discards_in_flight));

                        if (ca->discard) {
                                allocator_wait(ca, !list_empty(&ca->discards));
                                do_discard(ca, bucket);
                        } else {
                                fifo_push(&ca->free, bucket);
                                closure_wake_up(&ca->set->bucket_wait);
                        }
                }

                /*
                 * We've run out of free buckets, we need to find some buckets
                 * we can invalidate. First, invalidate them in memory and add
                 * them to the free_inc list:
                 */

                allocator_wait(ca, ca->set->gc_mark_valid &&
                               (ca->need_save_prio > 64 ||
                                !ca->invalidate_needs_gc));
                invalidate_buckets(ca);

                /*
                 * Now, we write their new gens to disk so we can start writing
                 * new stuff to them:
                 */
                allocator_wait(ca, !atomic_read(&ca->set->prio_blocked));
                if (CACHE_SYNC(&ca->set->sb) &&
                    (!fifo_empty(&ca->free_inc) ||
                     ca->need_save_prio > 64))
                        bch_prio_write(ca);
        }
}

long bch_bucket_alloc(struct cache *ca, unsigned watermark, struct closure *cl)
{
        long r = -1;
again:
        wake_up_process(ca->alloc_thread);

        if (fifo_used(&ca->free) > ca->watermark[watermark] &&
            fifo_pop(&ca->free, r)) {
                struct bucket *b = ca->buckets + r;
#ifdef CONFIG_BCACHE_EDEBUG
                size_t iter;
                long i;

                for (iter = 0; iter < prio_buckets(ca) * 2; iter++)
                        BUG_ON(ca->prio_buckets[iter] == (uint64_t) r);

                fifo_for_each(i, &ca->free, iter)
                        BUG_ON(i == r);
                fifo_for_each(i, &ca->free_inc, iter)
                        BUG_ON(i == r);
                fifo_for_each(i, &ca->unused, iter)
                        BUG_ON(i == r);
#endif
                BUG_ON(atomic_read(&b->pin) != 1);

                SET_GC_SECTORS_USED(b, ca->sb.bucket_size);

                if (watermark <= WATERMARK_METADATA) {
                        SET_GC_MARK(b, GC_MARK_METADATA);
                        b->prio = BTREE_PRIO;
                } else {
                        SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
                        b->prio = INITIAL_PRIO;
                }

                return r;
        }

        trace_bcache_alloc_fail(ca);

        if (cl) {
                closure_wait(&ca->set->bucket_wait, cl);

                if (closure_blocking(cl)) {
                        mutex_unlock(&ca->set->bucket_lock);
                        closure_sync(cl);
                        mutex_lock(&ca->set->bucket_lock);
                        goto again;
                }
        }

        return -1;
}

void bch_bucket_free(struct cache_set *c, struct bkey *k)
{
        unsigned i;

        for (i = 0; i < KEY_PTRS(k); i++) {
                struct bucket *b = PTR_BUCKET(c, k, i);

                SET_GC_MARK(b, GC_MARK_RECLAIMABLE);
                SET_GC_SECTORS_USED(b, 0);
                bch_bucket_add_unused(PTR_CACHE(c, k, i), b);
        }
}

int __bch_bucket_alloc_set(struct cache_set *c, unsigned watermark,
                           struct bkey *k, int n, struct closure *cl)
{
        int i;

        lockdep_assert_held(&c->bucket_lock);
        BUG_ON(!n || n > c->caches_loaded || n > 8);

        bkey_init(k);

        /* sort by free space/prio of oldest data in caches */

        for (i = 0; i < n; i++) {
                struct cache *ca = c->cache_by_alloc[i];
                long b = bch_bucket_alloc(ca, watermark, cl);

                if (b == -1)
                        goto err;

                k->ptr[i] = PTR(ca->buckets[b].gen,
                                bucket_to_sector(c, b),
                                ca->sb.nr_this_dev);

                SET_KEY_PTRS(k, i + 1);
        }

        return 0;
err:
        bch_bucket_free(c, k);
        __bkey_put(c, k);
        return -1;
}

int bch_bucket_alloc_set(struct cache_set *c, unsigned watermark,
                         struct bkey *k, int n, struct closure *cl)
{
        int ret;
        mutex_lock(&c->bucket_lock);
        ret = __bch_bucket_alloc_set(c, watermark, k, n, cl);
        mutex_unlock(&c->bucket_lock);
        return ret;
}

/* Init */

int bch_cache_allocator_start(struct cache *ca)
{
        struct task_struct *k = kthread_run(bch_allocator_thread,
                                            ca, "bcache_allocator");
        if (IS_ERR(k))
                return PTR_ERR(k);

        ca->alloc_thread = k;
        return 0;
}

void bch_cache_allocator_exit(struct cache *ca)
{
        struct discard *d;

        while (!list_empty(&ca->discards)) {
                d = list_first_entry(&ca->discards, struct discard, list);
                cancel_work_sync(&d->work);
                list_del(&d->list);
                kfree(d);
        }
}

int bch_cache_allocator_init(struct cache *ca)
{
        unsigned i;

        /*
         * Reserve:
         * Prio/gen writes first
         * Then 8 for btree allocations
         * Then half for the moving garbage collector
         */

        ca->watermark[WATERMARK_PRIO] = 0;

        ca->watermark[WATERMARK_METADATA] = prio_buckets(ca);

        ca->watermark[WATERMARK_MOVINGGC] = 8 +
                ca->watermark[WATERMARK_METADATA];

        ca->watermark[WATERMARK_NONE] = ca->free.size / 2 +
                ca->watermark[WATERMARK_MOVINGGC];

        for (i = 0; i < MAX_IN_FLIGHT_DISCARDS; i++) {
                struct discard *d = kzalloc(sizeof(*d), GFP_KERNEL);
                if (!d)
                        return -ENOMEM;

                d->ca = ca;
                INIT_WORK(&d->work, discard_finish);
                list_add(&d->list, &ca->discards);
        }

        return 0;
}