From cafe563591446cf80bfbc2fe3bc72a2e36cf1060 Mon Sep 17 00:00:00 2001 From: Kent Overstreet Date: Sat, 23 Mar 2013 16:11:31 -0700 Subject: bcache: A block layer cache Does writethrough and writeback caching, handles unclean shutdown, and has a bunch of other nifty features motivated by real world usage. See the wiki at http://bcache.evilpiepirate.org for more. Signed-off-by: Kent Overstreet --- drivers/md/bcache/writeback.c | 414 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 414 insertions(+) create mode 100644 drivers/md/bcache/writeback.c (limited to 'drivers/md/bcache/writeback.c') diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c new file mode 100644 index 00000000000..a80ee5373fd --- /dev/null +++ b/drivers/md/bcache/writeback.c @@ -0,0 +1,414 @@ +/* + * background writeback - scan btree for dirty data and write it to the backing + * device + * + * Copyright 2010, 2011 Kent Overstreet + * Copyright 2012 Google, Inc. + */ + +#include "bcache.h" +#include "btree.h" +#include "debug.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 = atomic_long_read(&dc->disk.sectors_dirty); + 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) +{ + if (atomic_read(&dc->disk.detaching) || + !dc->writeback_percent) + return 0; + + return next_delay(&dc->writeback_rate, sectors * 10000000ULL); +} + +/* Background writeback */ + +static bool dirty_pred(struct keybuf *buf, struct bkey *k) +{ + return KEY_DIRTY(k); +} + +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; + 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; + } + + bch_refill_keybuf(dc->disk.c, buf, &end); + + 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); + + 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, unsigned sectors) +{ + atomic_long_add(sectors, &dc->disk.sectors_dirty); + + 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); + } +} + +/* 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 = bio_iovec_idx(&io->bio, io->bio.bi_vcnt); + + while (bv-- != io->bio.bi_io_vec) + __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); + + pr_debug("clearing %s", pkey(&w->key)); + bch_btree_insert(&op, dc->disk.c); + closure_sync(&op.cl); + + 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); + atomic_dec_bug(&dc->in_flight); + + closure_wake_up(&dc->writeback_wait); + + 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; + + trace_bcache_write_dirty(&io->bio); + closure_bio_submit(&io->bio, cl, &io->dc->disk); + + continue_at(cl, write_dirty_finish, dirty_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); + + trace_bcache_read_dirty(&io->bio); + closure_bio_submit(&io->bio, cl, &io->dc->disk); + + continue_at(cl, write_dirty, dirty_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)) { + w->private = NULL; + + closure_delay(&dc->writeback, delay); + continue_at(cl, read_dirty, dirty_wq); + } + + 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; + + pr_debug("%s", pkey(&w->key)); + + closure_call(&io->cl, read_dirty_submit, NULL, &dc->disk.cl); + + delay = writeback_delay(dc, KEY_SIZE(&w->key)); + + atomic_inc(&dc->in_flight); + + if (!closure_wait_event(&dc->writeback_wait, cl, + atomic_read(&dc->in_flight) < 64)) + continue_at(cl, read_dirty, dirty_wq); + } + + if (0) { +err_free: + kfree(w->private); +err: + bch_keybuf_del(&dc->writeback_keys, w); + } + + refill_dirty(cl); +} + +void bch_writeback_init_cached_dev(struct cached_dev *dc) +{ + closure_init_unlocked(&dc->writeback); + init_rwsem(&dc->writeback_lock); + + bch_keybuf_init(&dc->writeback_keys, dirty_pred); + + 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_singlethread_workqueue("bcache_writeback"); + if (!dirty_wq) + return -ENOMEM; + + return 0; +} -- cgit v1.2.3