text: #ifndef _BCACHE_WRITEBACK_H
  #define _BCACHE_WRITEBACK_H
  
  #define CUTOFF_WRITEBACK	40
  #define CUTOFF_WRITEBACK_SYNC	70
  
  static inline uint64_t bcache_dev_sectors_dirty(struct bcache_device *d)
  {
  	uint64_t i, ret = 0;
  
  	for (i = 0; i < d->nr_stripes; i++)
  		ret += atomic_read(d->stripe_sectors_dirty + i);
  
  	return ret;
  }
  
  static inline uint64_t  bcache_flash_devs_sectors_dirty(struct cache_set *c)
  {
  	uint64_t i, ret = 0;
  
  	mutex_lock(&bch_register_lock);
  
  	for (i = 0; i < c->nr_uuids; i++) {
  		struct bcache_device *d = c->devices[i];
  
  		if (!d || !UUID_FLASH_ONLY(&c->uuids[i]))
  			continue;
  	   ret += bcache_dev_sectors_dirty(d);
  	}
  
  	mutex_unlock(&bch_register_lock);
  
  	return ret;
  }
  
  static inline unsigned offset_to_stripe(struct bcache_device *d,
  					uint64_t offset)
  {
  	do_div(offset, d->stripe_size);
  	return offset;
  }
  
  static inline bool bcache_dev_stripe_dirty(struct cached_dev *dc,
  					   uint64_t offset,
  					   unsigned nr_sectors)
  {
  	unsigned stripe = offset_to_stripe(&dc->disk, offset);
  
  	while (1) {
  		if (atomic_read(dc->disk.stripe_sectors_dirty + stripe))
  			return true;
  
  		if (nr_sectors <= dc->disk.stripe_size)
  			return false;
  
  		nr_sectors -= dc->disk.stripe_size;
  		stripe++;
  	}
  }
  
  static inline bool should_writeback(struct cached_dev *dc, struct bio *bio,
  				    unsigned cache_mode, bool would_skip)
  {
  	unsigned in_use = dc->disk.c->gc_stats.in_use;
  
  	if (cache_mode != CACHE_MODE_WRITEBACK ||
  	    test_bit(BCACHE_DEV_DETACHING, &dc->disk.flags) ||
  	    in_use > CUTOFF_WRITEBACK_SYNC)
  		return false;
  
  	if (dc->partial_stripes_expensive &&
  	    bcache_dev_stripe_dirty(dc, bio->bi_iter.bi_sector,
  				    bio_sectors(bio)))
  		return true;
  
  	if (would_skip)
  		return false;
  
  	return bio->bi_opf & REQ_SYNC ||
  		in_use <= CUTOFF_WRITEBACK;
  }
  
  static inline void bch_writeback_queue(struct cached_dev *dc)
  {
  	if (!IS_ERR_OR_NULL(dc->writeback_thread))
  		wake_up_process(dc->writeback_thread);
  }
  
  static inline 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);
  	}
  }
  
  void bcache_dev_sectors_dirty_add(struct cache_set *, unsigned, uint64_t, int);
  
  void bch_sectors_dirty_init(struct bcache_device *);
  void bch_cached_dev_writeback_init(struct cached_dev *);
  int bch_cached_dev_writeback_start(struct cached_dev *);
  
  #endif
  