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 <koverstreet@google.com>
diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
new file mode 100644
index 0000000..a80ee53
--- /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 <kent.overstreet@gmail.com>
+ * 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;
+}