Adding upstream version 4.19.249.upstream/4.19.249

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 826 insertions, 0 deletions

diff --git a/drivers/md/bcache/writeback.c b/drivers/md/bcache/writeback.c
new file mode 100644
index 000000000..aa58833fb
--- /dev/null
+++ b/drivers/md/bcache/writeback.c
@@ -0,0 +1,826 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * 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 <linux/delay.h>
+#include <linux/kthread.h>
+#include <linux/sched/clock.h>
+#include <trace/events/bcache.h>
+
+/* Rate limiting */
+static uint64_t __calc_target_rate(struct cached_dev *dc)
+{
+	struct cache_set *c = dc->disk.c;
+
+	/*
+	 * This is the size of the cache, minus the amount used for
+	 * flash-only devices
+	 */
+	uint64_t cache_sectors = c->nbuckets * c->sb.bucket_size -
+				atomic_long_read(&c->flash_dev_dirty_sectors);
+
+	/*
+	 * Unfortunately there is no control of global dirty data.  If the
+	 * user states that they want 10% dirty data in the cache, and has,
+	 * e.g., 5 backing volumes of equal size, we try and ensure each
+	 * backing volume uses about 2% of the cache for dirty data.
+	 */
+	uint32_t bdev_share =
+		div64_u64(bdev_sectors(dc->bdev) << WRITEBACK_SHARE_SHIFT,
+				c->cached_dev_sectors);
+
+	uint64_t cache_dirty_target =
+		div_u64(cache_sectors * dc->writeback_percent, 100);
+
+	/* Ensure each backing dev gets at least one dirty share */
+	if (bdev_share < 1)
+		bdev_share = 1;
+
+	return (cache_dirty_target * bdev_share) >> WRITEBACK_SHARE_SHIFT;
+}
+
+static void __update_writeback_rate(struct cached_dev *dc)
+{
+	/*
+	 * PI controller:
+	 * Figures out the amount that should be written per second.
+	 *
+	 * First, the error (number of sectors that are dirty beyond our
+	 * target) is calculated.  The error is accumulated (numerically
+	 * integrated).
+	 *
+	 * Then, the proportional value and integral value are scaled
+	 * based on configured values.  These are stored as inverses to
+	 * avoid fixed point math and to make configuration easy-- e.g.
+	 * the default value of 40 for writeback_rate_p_term_inverse
+	 * attempts to write at a rate that would retire all the dirty
+	 * blocks in 40 seconds.
+	 *
+	 * The writeback_rate_i_inverse value of 10000 means that 1/10000th
+	 * of the error is accumulated in the integral term per second.
+	 * This acts as a slow, long-term average that is not subject to
+	 * variations in usage like the p term.
+	 */
+	int64_t target = __calc_target_rate(dc);
+	int64_t dirty = bcache_dev_sectors_dirty(&dc->disk);
+	int64_t error = dirty - target;
+	int64_t proportional_scaled =
+		div_s64(error, dc->writeback_rate_p_term_inverse);
+	int64_t integral_scaled;
+	uint32_t new_rate;
+
+	if ((error < 0 && dc->writeback_rate_integral > 0) ||
+	    (error > 0 && time_before64(local_clock(),
+			 dc->writeback_rate.next + NSEC_PER_MSEC))) {
+		/*
+		 * Only decrease the integral term if it's more than
+		 * zero.  Only increase the integral term if the device
+		 * is keeping up.  (Don't wind up the integral
+		 * ineffectively in either case).
+		 *
+		 * It's necessary to scale this by
+		 * writeback_rate_update_seconds to keep the integral
+		 * term dimensioned properly.
+		 */
+		dc->writeback_rate_integral += error *
+			dc->writeback_rate_update_seconds;
+	}
+
+	integral_scaled = div_s64(dc->writeback_rate_integral,
+			dc->writeback_rate_i_term_inverse);
+
+	new_rate = clamp_t(int32_t, (proportional_scaled + integral_scaled),
+			dc->writeback_rate_minimum, NSEC_PER_SEC);
+
+	dc->writeback_rate_proportional = proportional_scaled;
+	dc->writeback_rate_integral_scaled = integral_scaled;
+	dc->writeback_rate_change = new_rate -
+			atomic_long_read(&dc->writeback_rate.rate);
+	atomic_long_set(&dc->writeback_rate.rate, new_rate);
+	dc->writeback_rate_target = target;
+}
+
+static bool set_at_max_writeback_rate(struct cache_set *c,
+				       struct cached_dev *dc)
+{
+	/*
+	 * Idle_counter is increased everytime when update_writeback_rate() is
+	 * called. If all backing devices attached to the same cache set have
+	 * identical dc->writeback_rate_update_seconds values, it is about 6
+	 * rounds of update_writeback_rate() on each backing device before
+	 * c->at_max_writeback_rate is set to 1, and then max wrteback rate set
+	 * to each dc->writeback_rate.rate.
+	 * In order to avoid extra locking cost for counting exact dirty cached
+	 * devices number, c->attached_dev_nr is used to calculate the idle
+	 * throushold. It might be bigger if not all cached device are in write-
+	 * back mode, but it still works well with limited extra rounds of
+	 * update_writeback_rate().
+	 */
+	if (atomic_inc_return(&c->idle_counter) <
+	    atomic_read(&c->attached_dev_nr) * 6)
+		return false;
+
+	if (atomic_read(&c->at_max_writeback_rate) != 1)
+		atomic_set(&c->at_max_writeback_rate, 1);
+
+	atomic_long_set(&dc->writeback_rate.rate, INT_MAX);
+
+	/* keep writeback_rate_target as existing value */
+	dc->writeback_rate_proportional = 0;
+	dc->writeback_rate_integral_scaled = 0;
+	dc->writeback_rate_change = 0;
+
+	/*
+	 * Check c->idle_counter and c->at_max_writeback_rate agagain in case
+	 * new I/O arrives during before set_at_max_writeback_rate() returns.
+	 * Then the writeback rate is set to 1, and its new value should be
+	 * decided via __update_writeback_rate().
+	 */
+	if ((atomic_read(&c->idle_counter) <
+	     atomic_read(&c->attached_dev_nr) * 6) ||
+	    !atomic_read(&c->at_max_writeback_rate))
+		return false;
+
+	return true;
+}
+
+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);
+	struct cache_set *c = dc->disk.c;
+
+	/*
+	 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
+	 * cancel_delayed_work_sync().
+	 */
+	set_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
+	/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
+	smp_mb();
+
+	/*
+	 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
+	 * check it here too.
+	 */
+	if (!test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) ||
+	    test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
+		clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
+		/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
+		smp_mb();
+		return;
+	}
+
+	if (atomic_read(&dc->has_dirty) && dc->writeback_percent) {
+		/*
+		 * If the whole cache set is idle, set_at_max_writeback_rate()
+		 * will set writeback rate to a max number. Then it is
+		 * unncessary to update writeback rate for an idle cache set
+		 * in maximum writeback rate number(s).
+		 */
+		if (!set_at_max_writeback_rate(c, dc)) {
+			down_read(&dc->writeback_lock);
+			__update_writeback_rate(dc);
+			up_read(&dc->writeback_lock);
+		}
+	}
+
+
+	/*
+	 * CACHE_SET_IO_DISABLE might be set via sysfs interface,
+	 * check it here too.
+	 */
+	if (test_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags) &&
+	    !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
+		schedule_delayed_work(&dc->writeback_rate_update,
+			      dc->writeback_rate_update_seconds * HZ);
+	}
+
+	/*
+	 * should check BCACHE_DEV_RATE_DW_RUNNING before calling
+	 * cancel_delayed_work_sync().
+	 */
+	clear_bit(BCACHE_DEV_RATE_DW_RUNNING, &dc->disk.flags);
+	/* paired with where BCACHE_DEV_RATE_DW_RUNNING is tested */
+	smp_mb();
+}
+
+static unsigned int writeback_delay(struct cached_dev *dc,
+				    unsigned int sectors)
+{
+	if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
+	    !dc->writeback_percent)
+		return 0;
+
+	return bch_next_delay(&dc->writeback_rate, sectors);
+}
+
+struct dirty_io {
+	struct closure		cl;
+	struct cached_dev	*dc;
+	uint16_t		sequence;
+	struct bio		bio;
+};
+
+static void dirty_init(struct keybuf_key *w)
+{
+	struct dirty_io *io = w->private;
+	struct bio *bio = &io->bio;
+
+	bio_init(bio, bio->bi_inline_vecs,
+		 DIV_ROUND_UP(KEY_SIZE(&w->key), PAGE_SECTORS));
+	if (!io->dc->writeback_percent)
+		bio_set_prio(bio, IOPRIO_PRIO_VALUE(IOPRIO_CLASS_IDLE, 0));
+
+	bio->bi_iter.bi_size	= KEY_SIZE(&w->key) << 9;
+	bio->bi_private		= w;
+	bch_bio_map(bio, NULL);
+}
+
+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;
+
+	bio_free_pages(&io->bio);
+
+	/* This is kind of a dumb way of signalling errors. */
+	if (KEY_DIRTY(&w->key)) {
+		int ret;
+		unsigned int i;
+		struct keylist keys;
+
+		bch_keylist_init(&keys);
+
+		bkey_copy(keys.top, &w->key);
+		SET_KEY_DIRTY(keys.top, false);
+		bch_keylist_push(&keys);
+
+		for (i = 0; i < KEY_PTRS(&w->key); i++)
+			atomic_inc(&PTR_BUCKET(dc->disk.c, &w->key, i)->pin);
+
+		ret = bch_btree_insert(dc->disk.c, &keys, NULL, &w->key);
+
+		if (ret)
+			trace_bcache_writeback_collision(&w->key);
+
+		atomic_long_inc(ret
+				? &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)
+{
+	struct keybuf_key *w = bio->bi_private;
+	struct dirty_io *io = w->private;
+
+	if (bio->bi_status) {
+		SET_KEY_DIRTY(&w->key, false);
+		bch_count_backing_io_errors(io->dc, bio);
+	}
+
+	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;
+	struct cached_dev *dc = io->dc;
+
+	uint16_t next_sequence;
+
+	if (atomic_read(&dc->writeback_sequence_next) != io->sequence) {
+		/* Not our turn to write; wait for a write to complete */
+		closure_wait(&dc->writeback_ordering_wait, cl);
+
+		if (atomic_read(&dc->writeback_sequence_next) == io->sequence) {
+			/*
+			 * Edge case-- it happened in indeterminate order
+			 * relative to when we were added to wait list..
+			 */
+			closure_wake_up(&dc->writeback_ordering_wait);
+		}
+
+		continue_at(cl, write_dirty, io->dc->writeback_write_wq);
+		return;
+	}
+
+	next_sequence = io->sequence + 1;
+
+	/*
+	 * IO errors are signalled using the dirty bit on the key.
+	 * If we failed to read, we should not attempt to write to the
+	 * backing device.  Instead, immediately go to write_dirty_finish
+	 * to clean up.
+	 */
+	if (KEY_DIRTY(&w->key)) {
+		dirty_init(w);
+		bio_set_op_attrs(&io->bio, REQ_OP_WRITE, 0);
+		io->bio.bi_iter.bi_sector = KEY_START(&w->key);
+		bio_set_dev(&io->bio, io->dc->bdev);
+		io->bio.bi_end_io	= dirty_endio;
+
+		/* I/O request sent to backing device */
+		closure_bio_submit(io->dc->disk.c, &io->bio, cl);
+	}
+
+	atomic_set(&dc->writeback_sequence_next, next_sequence);
+	closure_wake_up(&dc->writeback_ordering_wait);
+
+	continue_at(cl, write_dirty_finish, io->dc->writeback_write_wq);
+}
+
+static void read_dirty_endio(struct bio *bio)
+{
+	struct keybuf_key *w = bio->bi_private;
+	struct dirty_io *io = w->private;
+
+	/* is_read = 1 */
+	bch_count_io_errors(PTR_CACHE(io->dc->disk.c, &w->key, 0),
+			    bio->bi_status, 1,
+			    "reading dirty data from cache");
+
+	dirty_endio(bio);
+}
+
+static void read_dirty_submit(struct closure *cl)
+{
+	struct dirty_io *io = container_of(cl, struct dirty_io, cl);
+
+	closure_bio_submit(io->dc->disk.c, &io->bio, cl);
+
+	continue_at(cl, write_dirty, io->dc->writeback_write_wq);
+}
+
+static void read_dirty(struct cached_dev *dc)
+{
+	unsigned int delay = 0;
+	struct keybuf_key *next, *keys[MAX_WRITEBACKS_IN_PASS], *w;
+	size_t size;
+	int nk, i;
+	struct dirty_io *io;
+	struct closure cl;
+	uint16_t sequence = 0;
+
+	BUG_ON(!llist_empty(&dc->writeback_ordering_wait.list));
+	atomic_set(&dc->writeback_sequence_next, sequence);
+	closure_init_stack(&cl);
+
+	/*
+	 * XXX: if we error, background writeback just spins. Should use some
+	 * mempools.
+	 */
+
+	next = bch_keybuf_next(&dc->writeback_keys);
+
+	while (!kthread_should_stop() &&
+	       !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
+	       next) {
+		size = 0;
+		nk = 0;
+
+		do {
+			BUG_ON(ptr_stale(dc->disk.c, &next->key, 0));
+
+			/*
+			 * Don't combine too many operations, even if they
+			 * are all small.
+			 */
+			if (nk >= MAX_WRITEBACKS_IN_PASS)
+				break;
+
+			/*
+			 * If the current operation is very large, don't
+			 * further combine operations.
+			 */
+			if (size >= MAX_WRITESIZE_IN_PASS)
+				break;
+
+			/*
+			 * Operations are only eligible to be combined
+			 * if they are contiguous.
+			 *
+			 * TODO: add a heuristic willing to fire a
+			 * certain amount of non-contiguous IO per pass,
+			 * so that we can benefit from backing device
+			 * command queueing.
+			 */
+			if ((nk != 0) && bkey_cmp(&keys[nk-1]->key,
+						&START_KEY(&next->key)))
+				break;
+
+			size += KEY_SIZE(&next->key);
+			keys[nk++] = next;
+		} while ((next = bch_keybuf_next(&dc->writeback_keys)));
+
+		/* Now we have gathered a set of 1..5 keys to write back. */
+		for (i = 0; i < nk; i++) {
+			w = keys[i];
+
+			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;
+			io->sequence    = sequence++;
+
+			dirty_init(w);
+			bio_set_op_attrs(&io->bio, REQ_OP_READ, 0);
+			io->bio.bi_iter.bi_sector = PTR_OFFSET(&w->key, 0);
+			bio_set_dev(&io->bio,
+				    PTR_CACHE(dc->disk.c, &w->key, 0)->bdev);
+			io->bio.bi_end_io	= read_dirty_endio;
+
+			if (bch_bio_alloc_pages(&io->bio, GFP_KERNEL))
+				goto err_free;
+
+			trace_bcache_writeback(&w->key);
+
+			down(&dc->in_flight);
+
+			/*
+			 * We've acquired a semaphore for the maximum
+			 * simultaneous number of writebacks; from here
+			 * everything happens asynchronously.
+			 */
+			closure_call(&io->cl, read_dirty_submit, NULL, &cl);
+		}
+
+		delay = writeback_delay(dc, size);
+
+		while (!kthread_should_stop() &&
+		       !test_bit(CACHE_SET_IO_DISABLE, &dc->disk.c->flags) &&
+		       delay) {
+			schedule_timeout_interruptible(delay);
+			delay = writeback_delay(dc, 0);
+		}
+	}
+
+	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
+	 */
+	closure_sync(&cl);
+}
+
+/* Scan for dirty data */
+
+void bcache_dev_sectors_dirty_add(struct cache_set *c, unsigned int inode,
+				  uint64_t offset, int nr_sectors)
+{
+	struct bcache_device *d = c->devices[inode];
+	unsigned int stripe_offset, sectors_dirty;
+	int stripe;
+
+	if (!d)
+		return;
+
+	stripe = offset_to_stripe(d, offset);
+	if (stripe < 0)
+		return;
+
+	if (UUID_FLASH_ONLY(&c->uuids[inode]))
+		atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
+
+	stripe_offset = offset & (d->stripe_size - 1);
+
+	while (nr_sectors) {
+		int s = min_t(unsigned int, abs(nr_sectors),
+			      d->stripe_size - stripe_offset);
+
+		if (nr_sectors < 0)
+			s = -s;
+
+		if (stripe >= d->nr_stripes)
+			return;
+
+		sectors_dirty = atomic_add_return(s,
+					d->stripe_sectors_dirty + stripe);
+		if (sectors_dirty == d->stripe_size)
+			set_bit(stripe, d->full_dirty_stripes);
+		else
+			clear_bit(stripe, d->full_dirty_stripes);
+
+		nr_sectors -= s;
+		stripe_offset = 0;
+		stripe++;
+	}
+}
+
+static bool dirty_pred(struct keybuf *buf, struct bkey *k)
+{
+	struct cached_dev *dc = container_of(buf,
+					     struct cached_dev,
+					     writeback_keys);
+
+	BUG_ON(KEY_INODE(k) != dc->disk.id);
+
+	return KEY_DIRTY(k);
+}
+
+static void refill_full_stripes(struct cached_dev *dc)
+{
+	struct keybuf *buf = &dc->writeback_keys;
+	unsigned int start_stripe, next_stripe;
+	int stripe;
+	bool wrapped = false;
+
+	stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
+	if (stripe < 0)
+		stripe = 0;
+
+	start_stripe = stripe;
+
+	while (1) {
+		stripe = find_next_bit(dc->disk.full_dirty_stripes,
+				       dc->disk.nr_stripes, stripe);
+
+		if (stripe == dc->disk.nr_stripes)
+			goto next;
+
+		next_stripe = find_next_zero_bit(dc->disk.full_dirty_stripes,
+						 dc->disk.nr_stripes, stripe);
+
+		buf->last_scanned = KEY(dc->disk.id,
+					stripe * dc->disk.stripe_size, 0);
+
+		bch_refill_keybuf(dc->disk.c, buf,
+				  &KEY(dc->disk.id,
+				       next_stripe * dc->disk.stripe_size, 0),
+				  dirty_pred);
+
+		if (array_freelist_empty(&buf->freelist))
+			return;
+
+		stripe = next_stripe;
+next:
+		if (wrapped && stripe > start_stripe)
+			return;
+
+		if (stripe == dc->disk.nr_stripes) {
+			stripe = 0;
+			wrapped = true;
+		}
+	}
+}
+
+/*
+ * Returns true if we scanned the entire disk
+ */
+static bool refill_dirty(struct cached_dev *dc)
+{
+	struct keybuf *buf = &dc->writeback_keys;
+	struct bkey start = KEY(dc->disk.id, 0, 0);
+	struct bkey end = KEY(dc->disk.id, MAX_KEY_OFFSET, 0);
+	struct bkey start_pos;
+
+	/*
+	 * make sure keybuf pos is inside the range for this disk - at bringup
+	 * we might not be attached yet so this disk's inode nr isn't
+	 * initialized then
+	 */
+	if (bkey_cmp(&buf->last_scanned, &start) < 0 ||
+	    bkey_cmp(&buf->last_scanned, &end) > 0)
+		buf->last_scanned = start;
+
+	if (dc->partial_stripes_expensive) {
+		refill_full_stripes(dc);
+		if (array_freelist_empty(&buf->freelist))
+			return false;
+	}
+
+	start_pos = buf->last_scanned;
+	bch_refill_keybuf(dc->disk.c, buf, &end, dirty_pred);
+
+	if (bkey_cmp(&buf->last_scanned, &end) < 0)
+		return false;
+
+	/*
+	 * If we get to the end start scanning again from the beginning, and
+	 * only scan up to where we initially started scanning from:
+	 */
+	buf->last_scanned = start;
+	bch_refill_keybuf(dc->disk.c, buf, &start_pos, dirty_pred);
+
+	return bkey_cmp(&buf->last_scanned, &start_pos) >= 0;
+}
+
+static int bch_writeback_thread(void *arg)
+{
+	struct cached_dev *dc = arg;
+	struct cache_set *c = dc->disk.c;
+	bool searched_full_index;
+
+	bch_ratelimit_reset(&dc->writeback_rate);
+
+	while (!kthread_should_stop() &&
+	       !test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
+		down_write(&dc->writeback_lock);
+		set_current_state(TASK_INTERRUPTIBLE);
+		/*
+		 * If the bache device is detaching, skip here and continue
+		 * to perform writeback. Otherwise, if no dirty data on cache,
+		 * or there is dirty data on cache but writeback is disabled,
+		 * the writeback thread should sleep here and wait for others
+		 * to wake up it.
+		 */
+		if (!test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) &&
+		    (!atomic_read(&dc->has_dirty) || !dc->writeback_running)) {
+			up_write(&dc->writeback_lock);
+
+			if (kthread_should_stop() ||
+			    test_bit(CACHE_SET_IO_DISABLE, &c->flags)) {
+				set_current_state(TASK_RUNNING);
+				break;
+			}
+
+			schedule();
+			continue;
+		}
+		set_current_state(TASK_RUNNING);
+
+		searched_full_index = refill_dirty(dc);
+
+		if (searched_full_index &&
+		    RB_EMPTY_ROOT(&dc->writeback_keys.keys)) {
+			atomic_set(&dc->has_dirty, 0);
+			SET_BDEV_STATE(&dc->sb, BDEV_STATE_CLEAN);
+			bch_write_bdev_super(dc, NULL);
+			/*
+			 * If bcache device is detaching via sysfs interface,
+			 * writeback thread should stop after there is no dirty
+			 * data on cache. BCACHE_DEV_DETACHING flag is set in
+			 * bch_cached_dev_detach().
+			 */
+			if (test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags)) {
+				up_write(&dc->writeback_lock);
+				break;
+			}
+		}
+
+		up_write(&dc->writeback_lock);
+
+		read_dirty(dc);
+
+		if (searched_full_index) {
+			unsigned int delay = dc->writeback_delay * HZ;
+
+			while (delay &&
+			       !kthread_should_stop() &&
+			       !test_bit(CACHE_SET_IO_DISABLE, &c->flags) &&
+			       !test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags))
+				delay = schedule_timeout_interruptible(delay);
+
+			bch_ratelimit_reset(&dc->writeback_rate);
+		}
+	}
+
+	if (dc->writeback_write_wq) {
+		flush_workqueue(dc->writeback_write_wq);
+		destroy_workqueue(dc->writeback_write_wq);
+	}
+	cached_dev_put(dc);
+	wait_for_kthread_stop();
+
+	return 0;
+}
+
+/* Init */
+#define INIT_KEYS_EACH_TIME	500000
+#define INIT_KEYS_SLEEP_MS	100
+
+struct sectors_dirty_init {
+	struct btree_op	op;
+	unsigned int	inode;
+	size_t		count;
+	struct bkey	start;
+};
+
+static int sectors_dirty_init_fn(struct btree_op *_op, struct btree *b,
+				 struct bkey *k)
+{
+	struct sectors_dirty_init *op = container_of(_op,
+						struct sectors_dirty_init, op);
+	if (KEY_INODE(k) > op->inode)
+		return MAP_DONE;
+
+	if (KEY_DIRTY(k))
+		bcache_dev_sectors_dirty_add(b->c, KEY_INODE(k),
+					     KEY_START(k), KEY_SIZE(k));
+
+	op->count++;
+	if (atomic_read(&b->c->search_inflight) &&
+	    !(op->count % INIT_KEYS_EACH_TIME)) {
+		bkey_copy_key(&op->start, k);
+		return -EAGAIN;
+	}
+
+	return MAP_CONTINUE;
+}
+
+void bch_sectors_dirty_init(struct bcache_device *d)
+{
+	struct sectors_dirty_init op;
+	int ret;
+
+	bch_btree_op_init(&op.op, -1);
+	op.inode = d->id;
+	op.count = 0;
+	op.start = KEY(op.inode, 0, 0);
+
+	do {
+		ret = bch_btree_map_keys(&op.op, d->c, &op.start,
+					 sectors_dirty_init_fn, 0);
+		if (ret == -EAGAIN)
+			schedule_timeout_interruptible(
+				msecs_to_jiffies(INIT_KEYS_SLEEP_MS));
+		else if (ret < 0) {
+			pr_warn("sectors dirty init failed, ret=%d!", ret);
+			break;
+		}
+	} while (ret == -EAGAIN);
+}
+
+void bch_cached_dev_writeback_init(struct cached_dev *dc)
+{
+	sema_init(&dc->in_flight, 64);
+	init_rwsem(&dc->writeback_lock);
+	bch_keybuf_init(&dc->writeback_keys);
+
+	dc->writeback_metadata		= true;
+	dc->writeback_running		= false;
+	dc->writeback_percent		= 10;
+	dc->writeback_delay		= 30;
+	atomic_long_set(&dc->writeback_rate.rate, 1024);
+	dc->writeback_rate_minimum	= 8;
+
+	dc->writeback_rate_update_seconds = WRITEBACK_RATE_UPDATE_SECS_DEFAULT;
+	dc->writeback_rate_p_term_inverse = 40;
+	dc->writeback_rate_i_term_inverse = 10000;
+
+	WARN_ON(test_and_clear_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
+	INIT_DELAYED_WORK(&dc->writeback_rate_update, update_writeback_rate);
+}
+
+int bch_cached_dev_writeback_start(struct cached_dev *dc)
+{
+	dc->writeback_write_wq = alloc_workqueue("bcache_writeback_wq",
+						WQ_MEM_RECLAIM, 0);
+	if (!dc->writeback_write_wq)
+		return -ENOMEM;
+
+	cached_dev_get(dc);
+	dc->writeback_thread = kthread_create(bch_writeback_thread, dc,
+					      "bcache_writeback");
+	if (IS_ERR(dc->writeback_thread)) {
+		cached_dev_put(dc);
+		destroy_workqueue(dc->writeback_write_wq);
+		return PTR_ERR(dc->writeback_thread);
+	}
+	dc->writeback_running = true;
+
+	WARN_ON(test_and_set_bit(BCACHE_DEV_WB_RUNNING, &dc->disk.flags));
+	schedule_delayed_work(&dc->writeback_rate_update,
+			      dc->writeback_rate_update_seconds * HZ);
+
+	bch_writeback_queue(dc);
+
+	return 0;
+}