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/*
* 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, stripe, sectors_dirty;
if (!d)
return;
if (UUID_FLASH_ONLY(&c->uuids[inode]))
atomic_long_add(nr_sectors, &c->flash_dev_dirty_sectors);
stripe = offset_to_stripe(d, offset);
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, stripe, next_stripe;
bool wrapped = false;
stripe = offset_to_stripe(&dc->disk, KEY_OFFSET(&buf->last_scanned));
if (stripe >= dc->disk.nr_stripes)
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);
}
}
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 = true;
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);
return PTR_ERR(dc->writeback_thread);
}
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;
}
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