bcache: Fix a dumb CPU spinning bug in writeback

[mirror_ubuntu-artful-kernel.git] / drivers / md / bcache / writeback.c

/*
 * background writeback - scan btree for dirty data and write it to the backing
 * device
 *
 * Copyright 2010, 2011 Kent Overstreet <kent.overstreet@gmail.com>
 * Copyright 2012 Google, Inc.
 */

#include "bcache.h"
#include "btree.h"
#include "debug.h"
#include "writeback.h"

#include <trace/events/bcache.h>

static struct workqueue_struct *dirty_wq;

static void read_dirty(struct closure *);

struct dirty_io {
        struct closure          cl;
        struct cached_dev       *dc;
        struct bio              bio;
};

/* Rate limiting */

static void __update_writeback_rate(struct cached_dev *dc)
{
        struct cache_set *c = dc->disk.c;
        uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size;
        uint64_t cache_dirty_target =
                div_u64(cache_sectors * dc->writeback_percent, 100);

        int64_t target = div64_u64(cache_dirty_target * bdev_sectors(dc->bdev),
                                   c->cached_dev_sectors);

        /* PD controller */

        int change = 0;
        int64_t error;
        int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
        int64_t derivative = dirty - dc->disk.sectors_dirty_last;

        dc->disk.sectors_dirty_last = dirty;

        derivative *= dc->writeback_rate_d_term;
        derivative = clamp(derivative, -dirty, dirty);

        derivative = ewma_add(dc->disk.sectors_dirty_derivative, derivative,
                              dc->writeback_rate_d_smooth, 0);

        /* Avoid divide by zero */
        if (!target)
                goto out;

        error = div64_s64((dirty + derivative - target) << 8, target);

        change = div_s64((dc->writeback_rate.rate * error) >> 8,
                         dc->writeback_rate_p_term_inverse);

        /* Don't increase writeback rate if the device isn't keeping up */
        if (change > 0 &&
            time_after64(local_clock(),
                         dc->writeback_rate.next + 10 * NSEC_PER_MSEC))
                change = 0;

        dc->writeback_rate.rate =
                clamp_t(int64_t, dc->writeback_rate.rate + change,
                        1, NSEC_PER_MSEC);
out:
        dc->writeback_rate_derivative = derivative;
        dc->writeback_rate_change = change;
        dc->writeback_rate_target = target;

        schedule_delayed_work(&dc->writeback_rate_update,
                              dc->writeback_rate_update_seconds * HZ);
}

static void update_writeback_rate(struct work_struct *work)
{
        struct cached_dev *dc = container_of(to_delayed_work(work),
                                             struct cached_dev,
                                             writeback_rate_update);

        down_read(&dc->writeback_lock);

        if (atomic_read(&dc->has_dirty) &&
            dc->writeback_percent)
                __update_writeback_rate(dc);

        up_read(&dc->writeback_lock);
}

static unsigned writeback_delay(struct cached_dev *dc, unsigned sectors)
{
        uint64_t ret;

        if (atomic_read(&dc->disk.detaching) ||
            !dc->writeback_percent)
                return 0;

        ret = bch_next_delay(&dc->writeback_rate, sectors * 10000000ULL);

        return min_t(uint64_t, ret, HZ);
}

/* Background writeback */

static bool dirty_pred(struct keybuf *buf, struct bkey *k)
{
        return KEY_DIRTY(k);
}

static bool dirty_full_stripe_pred(struct keybuf *buf, struct bkey *k)
{
        uint64_t stripe;
        unsigned nr_sectors = KEY_SIZE(k);
        struct cached_dev *dc = container_of(buf, struct cached_dev,
                                             writeback_keys);
        unsigned stripe_size = 1 << dc->disk.stripe_size_bits;

        if (!KEY_DIRTY(k))
                return false;

        stripe = KEY_START(k) >> dc->disk.stripe_size_bits;
        while (1) {
                if (atomic_read(dc->disk.stripe_sectors_dirty + stripe) !=
                    stripe_size)
                        return false;

                if (nr_sectors <= stripe_size)
                        return true;

                nr_sectors -= stripe_size;
                stripe++;
        }
}

static void dirty_init(struct keybuf_key *w)
{
        struct dirty_io *io = w->private;
        struct bio *bio = &io->bio;

        bio_init(bio);
        if (!io->dc->writeback_percent)
                bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));

        bio->bi_size            = KEY_SIZE(&w->key) << 9;
        bio->bi_max_vecs        = DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS);
        bio->bi_private         = w;
        bio->bi_io_vec          = bio->bi_inline_vecs;
        bch_bio_map(bio, NULL);
}

static void refill_dirty(struct closure *cl)
{
        struct cached_dev *dc = container_of(cl, struct cached_dev,
                                             writeback.cl);
        struct keybuf *buf = &dc->writeback_keys;
        bool searched_from_start = false;
        struct bkey end = MAX_KEY;
        SET_KEY_INODE(&end, dc->disk.id);

        if (!atomic_read(&dc->disk.detaching) &&
            !dc->writeback_running)
                closure_return(cl);

        down_write(&dc->writeback_lock);

        if (!atomic_read(&dc->has_dirty)) {
                SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
                bch_write_bdev_super(dc, NULL);

                up_write(&dc->writeback_lock);
                closure_return(cl);
        }

        if (bkey_cmp(&buf->last_scanned, &end) >= 0) {
                buf->last_scanned = KEY(dc->disk.id, 0, 0);
                searched_from_start = true;
        }

        if (dc->partial_stripes_expensive) {
                uint64_t i;

                for (i = 0; i < dc->disk.nr_stripes; i++)
                        if (atomic_read(dc->disk.stripe_sectors_dirty + i) ==
                            1 << dc->disk.stripe_size_bits)
                                goto full_stripes;

                goto normal_refill;
full_stripes:
                bch_refill_keybuf(dc->disk.c, buf, &end,
                                  dirty_full_stripe_pred);
        } else {
normal_refill:
                bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
        }

        if (bkey_cmp(&buf->last_scanned, &end) >= 0 && searched_from_start) {
                /* Searched the entire btree  - delay awhile */

                if (RB_EMPTY_ROOT(&buf->keys)) {
                        atomic_set(&dc->has_dirty, 0);
                        cached_dev_put(dc);
                }

                if (!atomic_read(&dc->disk.detaching))
                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);
        }

        up_write(&dc->writeback_lock);

        bch_ratelimit_reset(&dc->writeback_rate);

        /* Punt to workqueue only so we don't recurse and blow the stack */
        continue_at(cl, read_dirty, dirty_wq);
}

void bch_writeback_queue(struct cached_dev *dc)
{
        if (closure_trylock(&dc->writeback.cl, &dc->disk.cl)) {
                if (!atomic_read(&dc->disk.detaching))
                        closure_delay(&dc->writeback, dc->writeback_delay * HZ);

                continue_at(&dc->writeback.cl, refill_dirty, dirty_wq);
        }
}

void bch_writeback_add(struct cached_dev *dc)
{
        if (!atomic_read(&dc->has_dirty) &&
            !atomic_xchg(&dc->has_dirty, 1)) {
                atomic_inc(&dc->count);

                if (BDEV_STATE(&dc->sb) != BDEV_STATE_DIRTY) {
                        SET_BDEV_STATE(&dc->sb, BDEV_STATE_DIRTY);
                        /* XXX: should do this synchronously */
                        bch_write_bdev_super(dc, NULL);
                }

                bch_writeback_queue(dc);

                if (dc->writeback_percent)
                        schedule_delayed_work(&dc->writeback_rate_update,
                                      dc->writeback_rate_update_seconds * HZ);
        }
}

void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned inode,
                                  uint64_t offset, int nr_sectors)
{
        struct bcache_device *d = c->devices[inode];
        unsigned stripe_size, stripe_offset;
        uint64_t stripe;

        if (!d)
                return;

        stripe_size = 1 << d->stripe_size_bits;
        stripe = offset >> d->stripe_size_bits;
        stripe_offset = offset & (stripe_size - 1);

        while (nr_sectors) {
                int s = min_t(unsigned, abs(nr_sectors),
                              stripe_size - stripe_offset);

                if (nr_sectors < 0)
                        s = -s;

                atomic_add(s, d->stripe_sectors_dirty + stripe);
                nr_sectors -= s;
                stripe_offset = 0;
                stripe++;
        }
}

/* Background writeback - IO loop */

static void dirty_io_destructor(struct closure *cl)
{
        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
        kfree(io);
}

static void write_dirty_finish(struct closure *cl)
{
        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
        struct keybuf_key *w = io->bio.bi_private;
        struct cached_dev *dc = io->dc;
        struct bio_vec *bv;
        int i;

        bio_for_each_segment_all(bv, &io->bio, i)
                __free_page(bv->bv_page);

        /* This is kind of a dumb way of signalling errors. */
        if (KEY_DIRTY(&w->key)) {
                unsigned i;
                struct btree_op op;
                bch_btree_op_init_stack(&op);

                op.type = BTREE_REPLACE;
                bkey_copy(&op.replace, &w->key);

                SET_KEY_DIRTY(&w->key, false);
                bch_keylist_add(&op.keys, &w->key);

                for (i = 0; i < KEY_PTRS(&w->key); i++)
                        atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);

                bch_btree_insert(&op, dc->disk.c);
                closure_sync(&op.cl);

                if (op.insert_collision)
                        trace_bcache_writeback_collision(&w->key);

                atomic_long_inc(op.insert_collision
                                ? &dc->disk.c->writeback_keys_failed
                                : &dc->disk.c->writeback_keys_done);
        }

        bch_keybuf_del(&dc->writeback_keys, w);
        up(&dc->in_flight);

        closure_return_with_destructor(cl, dirty_io_destructor);
}

static void dirty_endio(struct bio *bio, int error)
{
        struct keybuf_key *w = bio->bi_private;
        struct dirty_io *io = w->private;

        if (error)
                SET_KEY_DIRTY(&w->key, false);

        closure_put(&io->cl);
}

static void write_dirty(struct closure *cl)
{
        struct dirty_io *io = container_of(cl, struct dirty_io, cl);
        struct keybuf_key *w = io->bio.bi_private;

        dirty_init(w);
        io->bio.bi_rw           = WRITE;
        io->bio.bi_sector       = KEY_START(&w->key);
        io->bio.bi_bdev         = io->dc->bdev;
        io->bio.bi_end_io       = dirty_endio;

        closure_bio_submit(&io->bio, cl, &io->dc->disk);

        continue_at(cl, write_dirty_finish, system_wq);
}

static void read_dirty_endio(struct bio *bio, int error)
{
        struct keybuf_key *w = bio->bi_private;
        struct dirty_io *io = w->private;

        bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
                            error, "reading dirty data from cache");

        dirty_endio(bio, error);
}

static void read_dirty_submit(struct closure *cl)
{
        struct dirty_io *io = container_of(cl, struct dirty_io, cl);

        closure_bio_submit(&io->bio, cl, &io->dc->disk);

        continue_at(cl, write_dirty, system_wq);
}

static void read_dirty(struct closure *cl)
{
        struct cached_dev *dc = container_of(cl, struct cached_dev,
                                             writeback.cl);
        unsigned delay = writeback_delay(dc, 0);
        struct keybuf_key *w;
        struct dirty_io *io;

        /*
         * XXX: if we error, background writeback just spins. Should use some
         * mempools.
         */

        while (1) {
                w = bch_keybuf_next(&dc->writeback_keys);
                if (!w)
                        break;

                BUG_ON(ptr_stale(dc->disk.c, &w->key, 0));

                if (delay > 0 &&
                    (KEY_START(&w->key) != dc->last_read ||
                     jiffies_to_msecs(delay) > 50))
                        delay = schedule_timeout_uninterruptible(delay);

                dc->last_read   = KEY_OFFSET(&w->key);

                io = kzalloc(sizeof(struct dirty_io) + sizeof(struct bio_vec)
                             * DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS),
                             GFP_KERNEL);
                if (!io)
                        goto err;

                w->private      = io;
                io->dc          = dc;

                dirty_init(w);
                io->bio.bi_sector       = PTR_OFFSET(&w->key, 0);
                io->bio.bi_bdev         = PTR_CACHE(dc->disk.c,
                                                    &w->key, 0)->bdev;
                io->bio.bi_rw           = READ;
                io->bio.bi_end_io       = read_dirty_endio;

                if (bio_alloc_pages(&io->bio, GFP_KERNEL))
                        goto err_free;

                trace_bcache_writeback(&w->key);

                down(&dc->in_flight);
                closure_call(&io->cl, read_dirty_submit, NULL, cl);

                delay = writeback_delay(dc, KEY_SIZE(&w->key));
        }

        if (0) {
err_free:
                kfree(w->private);
err:
                bch_keybuf_del(&dc->writeback_keys, w);
        }

        /*
         * Wait for outstanding writeback IOs to finish (and keybuf slots to be
         * freed) before refilling again
         */
        continue_at(cl, refill_dirty, dirty_wq);
}

/* Init */

static int bch_btree_sectors_dirty_init(struct btree *b, struct btree_op *op,
                                        struct cached_dev *dc)
{
        struct bkey *k;
        struct btree_iter iter;

        bch_btree_iter_init(b, &iter, &KEY(dc->disk.id, 0, 0));
        while ((k = bch_btree_iter_next_filter(&iter, b, bch_ptr_bad)))
                if (!b->level) {
                        if (KEY_INODE(k) > dc->disk.id)
                                break;

                        if (KEY_DIRTY(k))
                                bcache_dev_sectors_dirty_add(b->c, dc->disk.id,
                                                             KEY_START(k),
                                                             KEY_SIZE(k));
                } else {
                        btree(sectors_dirty_init, k, b, op, dc);
                        if (KEY_INODE(k) > dc->disk.id)
                                break;

                        cond_resched();
                }

        return 0;
}

void bch_sectors_dirty_init(struct cached_dev *dc)
{
        struct btree_op op;

        bch_btree_op_init_stack(&op);
        btree_root(sectors_dirty_init, dc->disk.c, &op, dc);
}

void bch_cached_dev_writeback_init(struct cached_dev *dc)
{
        sema_init(&dc->in_flight, 64);
        closure_init_unlocked(&dc->writeback);
        init_rwsem(&dc->writeback_lock);

        bch_keybuf_init(&dc->writeback_keys);

        dc->writeback_metadata          = true;
        dc->writeback_running           = true;
        dc->writeback_percent           = 10;
        dc->writeback_delay             = 30;
        dc->writeback_rate.rate         = 1024;

        dc->writeback_rate_update_seconds = 30;
        dc->writeback_rate_d_term       = 16;
        dc->writeback_rate_p_term_inverse = 64;
        dc->writeback_rate_d_smooth     = 8;

        INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
        schedule_delayed_work(&dc->writeback_rate_update,
                              dc->writeback_rate_update_seconds * HZ);
}

void bch_writeback_exit(void)
{
        if (dirty_wq)
                destroy_workqueue(dirty_wq);
}

int __init bch_writeback_init(void)
{
        dirty_wq = create_workqueue("bcache_writeback");
        if (!dirty_wq)
                return -ENOMEM;

        return 0;
}