Re: [PATCH 03/10] writeback: move bandwidth related fields from backing_dev_info into bdi_writeback

[Jan Kara <jack@suse.cz>]

On Tue 18-11-14 03:37:21, Tejun Heo wrote:
> Currently, a bdi (backing_dev_info) embeds single wb (bdi_writeback)
> and the role of the separation is unclear.  For cgroup support for
> writeback IOs, a bdi will be updated to host multiple wb's where each
> wb serves writeback IOs of a different cgroup on the bdi.  To achieve
> that, a wb should carry all states necessary for servicing writeback
> IOs for a cgroup independently.
> 
> This patch moves bandwidth related fields from backing_dev_info into
> bdi_writeback.
> 
> * The moved fields are: bw_time_stamp, dirtied_stamp, written_stamp,
>   write_bandwidth, avg_write_bandwidth, dirty_ratelimit,
>   balanced_dirty_ratelimit, completions and dirty_exceeded.
> 
> * writeback_chunk_size() and over_bgroup_thresh() now take @wb instead
>   of @bdi.
> 
> * bdi_writeout_fraction(bdi, ...)	-> wb_writeout_fraction(wb, ...)
>   bdi_dirty_limit(bdi, ...)		-> wb_dirty_limit(wb, ...)
>   bdi_position_ration(bdi, ...)		-> wb_position_ratio(wb, ...)
>   bdi_update_writebandwidth(bdi, ...)	-> wb_update_write_bandwidth(wb, ...)
>   [__]bdi_update_bandwidth(bdi, ...)	-> [__]wb_update_bandwidth(wb, ...)
>   bdi_{max|min}_pause(bdi, ...)		-> wb_{max|min}_pause(wb, ...)
>   bdi_dirty_limits(bdi, ...)		-> wb_dirty_limits(wb, ...)
> 
> * Init/exits of the relocated fields are moved to bdi_wb_init/exit()
>   respectively.  Note that explicit zeroing is dropped in the process
>   as wb's are cleared in entirety anyway.
> 
> * As there's still only one bdi_writeback per backing_dev_info, all
>   uses of bdi->stat[] are mechanically replaced with bdi->wb.stat[]
>   introducing no behavior changes.
  Ok, no problem with this patch but I wonder: When you are moving all the
dirty limiting logic to bdi_writeback, then how do you plan to interpret
min/max_ratio in presence of several bdi_writeback structures?

								Honza
> 
> Signed-off-by: Tejun Heo <tj@kernel.org>
> Cc: Jens Axboe <axboe@kernel.dk>
> Cc: Jan Kara <jack@suse.cz>
> Cc: Wu Fengguang <fengguang.wu@intel.com>
> Cc: Jaegeuk Kim <jaegeuk@kernel.org>
> Cc: Steven Whitehouse <swhiteho@redhat.com>
> ---
>  fs/f2fs/node.c                   |   2 +-
>  fs/fs-writeback.c                |  17 ++-
>  fs/gfs2/super.c                  |   2 +-
>  include/linux/backing-dev.h      |  20 ++--
>  include/linux/writeback.h        |  19 ++-
>  include/trace/events/writeback.h |   8 +-
>  mm/backing-dev.c                 |  45 ++++---
>  mm/page-writeback.c              | 246 ++++++++++++++++++++-------------------
>  8 files changed, 177 insertions(+), 182 deletions(-)
> 
> diff --git a/fs/f2fs/node.c b/fs/f2fs/node.c
> index 44b8afe..c53d94b 100644
> --- a/fs/f2fs/node.c
> +++ b/fs/f2fs/node.c
> @@ -43,7 +43,7 @@ bool available_free_memory(struct f2fs_sb_info *sbi, int type)
>  		mem_size = (nm_i->nat_cnt * sizeof(struct nat_entry)) >> 12;
>  		res = mem_size < ((val.totalram * nm_i->ram_thresh / 100) >> 2);
>  	} else if (type == DIRTY_DENTS) {
> -		if (sbi->sb->s_bdi->dirty_exceeded)
> +		if (sbi->sb->s_bdi->wb.dirty_exceeded)
>  			return false;
>  		mem_size = get_pages(sbi, F2FS_DIRTY_DENTS);
>  		res = mem_size < ((val.totalram * nm_i->ram_thresh / 100) >> 1);
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index f5ca16e..daa91ae 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -574,7 +574,7 @@ out:
>  	return ret;
>  }
>  
> -static long writeback_chunk_size(struct backing_dev_info *bdi,
> +static long writeback_chunk_size(struct bdi_writeback *wb,
>  				 struct wb_writeback_work *work)
>  {
>  	long pages;
> @@ -595,7 +595,7 @@ static long writeback_chunk_size(struct backing_dev_info *bdi,
>  	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
>  		pages = LONG_MAX;
>  	else {
> -		pages = min(bdi->avg_write_bandwidth / 2,
> +		pages = min(wb->avg_write_bandwidth / 2,
>  			    global_dirty_limit / DIRTY_SCOPE);
>  		pages = min(pages, work->nr_pages);
>  		pages = round_down(pages + MIN_WRITEBACK_PAGES,
> @@ -693,7 +693,7 @@ static long writeback_sb_inodes(struct super_block *sb,
>  		inode->i_state |= I_SYNC;
>  		spin_unlock(&inode->i_lock);
>  
> -		write_chunk = writeback_chunk_size(wb->bdi, work);
> +		write_chunk = writeback_chunk_size(wb, work);
>  		wbc.nr_to_write = write_chunk;
>  		wbc.pages_skipped = 0;
>  
> @@ -780,7 +780,7 @@ static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
>  	return nr_pages - work.nr_pages;
>  }
>  
> -static bool over_bground_thresh(struct backing_dev_info *bdi)
> +static bool over_bground_thresh(struct bdi_writeback *wb)
>  {
>  	unsigned long background_thresh, dirty_thresh;
>  
> @@ -790,8 +790,7 @@ static bool over_bground_thresh(struct backing_dev_info *bdi)
>  	    global_page_state(NR_UNSTABLE_NFS) > background_thresh)
>  		return true;
>  
> -	if (wb_stat(&bdi->wb, WB_RECLAIMABLE) >
> -				bdi_dirty_limit(bdi, background_thresh))
> +	if (wb_stat(wb, WB_RECLAIMABLE) > wb_dirty_limit(wb, background_thresh))
>  		return true;
>  
>  	return false;
> @@ -804,7 +803,7 @@ static bool over_bground_thresh(struct backing_dev_info *bdi)
>  static void wb_update_bandwidth(struct bdi_writeback *wb,
>  				unsigned long start_time)
>  {
> -	__bdi_update_bandwidth(wb->bdi, 0, 0, 0, 0, 0, start_time);
> +	__wb_update_bandwidth(wb, 0, 0, 0, 0, 0, start_time);
>  }
>  
>  /*
> @@ -856,7 +855,7 @@ static long wb_writeback(struct bdi_writeback *wb,
>  		 * For background writeout, stop when we are below the
>  		 * background dirty threshold
>  		 */
> -		if (work->for_background && !over_bground_thresh(wb->bdi))
> +		if (work->for_background && !over_bground_thresh(wb))
>  			break;
>  
>  		/*
> @@ -948,7 +947,7 @@ static unsigned long get_nr_dirty_pages(void)
>  
>  static long wb_check_background_flush(struct bdi_writeback *wb)
>  {
> -	if (over_bground_thresh(wb->bdi)) {
> +	if (over_bground_thresh(wb)) {
>  
>  		struct wb_writeback_work work = {
>  			.nr_pages	= LONG_MAX,
> diff --git a/fs/gfs2/super.c b/fs/gfs2/super.c
> index a346f56..4566c89 100644
> --- a/fs/gfs2/super.c
> +++ b/fs/gfs2/super.c
> @@ -755,7 +755,7 @@ static int gfs2_write_inode(struct inode *inode, struct writeback_control *wbc)
>  
>  	if (wbc->sync_mode == WB_SYNC_ALL)
>  		gfs2_log_flush(GFS2_SB(inode), ip->i_gl, NORMAL_FLUSH);
> -	if (bdi->dirty_exceeded)
> +	if (bdi->wb.dirty_exceeded)
>  		gfs2_ail1_flush(sdp, wbc);
>  	else
>  		filemap_fdatawrite(metamapping);
> diff --git a/include/linux/backing-dev.h b/include/linux/backing-dev.h
> index 92fed42..a077a8d 100644
> --- a/include/linux/backing-dev.h
> +++ b/include/linux/backing-dev.h
> @@ -59,16 +59,6 @@ struct bdi_writeback {
>  	spinlock_t list_lock;		/* protects the b_* lists */
>  
>  	struct percpu_counter stat[NR_WB_STAT_ITEMS];
> -};
> -
> -struct backing_dev_info {
> -	struct list_head bdi_list;
> -	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
> -	unsigned int capabilities; /* Device capabilities */
> -	congested_fn *congested_fn; /* Function pointer if device is md/dm */
> -	void *congested_data;	/* Pointer to aux data for congested func */
> -
> -	char *name;
>  
>  	unsigned long bw_time_stamp;	/* last time write bw is updated */
>  	unsigned long dirtied_stamp;
> @@ -87,6 +77,16 @@ struct backing_dev_info {
>  
>  	struct fprop_local_percpu completions;
>  	int dirty_exceeded;
> +};
> +
> +struct backing_dev_info {
> +	struct list_head bdi_list;
> +	unsigned long ra_pages;	/* max readahead in PAGE_CACHE_SIZE units */
> +	unsigned int capabilities; /* Device capabilities */
> +	congested_fn *congested_fn; /* Function pointer if device is md/dm */
> +	void *congested_data;	/* Pointer to aux data for congested func */
> +
> +	char *name;
>  
>  	unsigned int min_ratio;
>  	unsigned int max_ratio, max_prop_frac;
> diff --git a/include/linux/writeback.h b/include/linux/writeback.h
> index a219be9..6887eb5 100644
> --- a/include/linux/writeback.h
> +++ b/include/linux/writeback.h
> @@ -152,16 +152,15 @@ int dirty_writeback_centisecs_handler(struct ctl_table *, int,
>  				      void __user *, size_t *, loff_t *);
>  
>  void global_dirty_limits(unsigned long *pbackground, unsigned long *pdirty);
> -unsigned long bdi_dirty_limit(struct backing_dev_info *bdi,
> -			       unsigned long dirty);
> -
> -void __bdi_update_bandwidth(struct backing_dev_info *bdi,
> -			    unsigned long thresh,
> -			    unsigned long bg_thresh,
> -			    unsigned long dirty,
> -			    unsigned long bdi_thresh,
> -			    unsigned long bdi_dirty,
> -			    unsigned long start_time);
> +unsigned long wb_dirty_limit(struct bdi_writeback *wb, unsigned long dirty);
> +
> +void __wb_update_bandwidth(struct bdi_writeback *wb,
> +			   unsigned long thresh,
> +			   unsigned long bg_thresh,
> +			   unsigned long dirty,
> +			   unsigned long bdi_thresh,
> +			   unsigned long bdi_dirty,
> +			   unsigned long start_time);
>  
>  void page_writeback_init(void);
>  void balance_dirty_pages_ratelimited(struct address_space *mapping);
> diff --git a/include/trace/events/writeback.h b/include/trace/events/writeback.h
> index cee02d6..8622b5b 100644
> --- a/include/trace/events/writeback.h
> +++ b/include/trace/events/writeback.h
> @@ -373,13 +373,13 @@ TRACE_EVENT(bdi_dirty_ratelimit,
>  
>  	TP_fast_assign(
>  		strlcpy(__entry->bdi, dev_name(bdi->dev), 32);
> -		__entry->write_bw	= KBps(bdi->write_bandwidth);
> -		__entry->avg_write_bw	= KBps(bdi->avg_write_bandwidth);
> +		__entry->write_bw	= KBps(bdi->wb.write_bandwidth);
> +		__entry->avg_write_bw	= KBps(bdi->wb.avg_write_bandwidth);
>  		__entry->dirty_rate	= KBps(dirty_rate);
> -		__entry->dirty_ratelimit = KBps(bdi->dirty_ratelimit);
> +		__entry->dirty_ratelimit = KBps(bdi->wb.dirty_ratelimit);
>  		__entry->task_ratelimit	= KBps(task_ratelimit);
>  		__entry->balanced_dirty_ratelimit =
> -					  KBps(bdi->balanced_dirty_ratelimit);
> +					KBps(bdi->wb.balanced_dirty_ratelimit);
>  	),
>  
>  	TP_printk("bdi %s: "
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index 4b6f650..7b9b10e 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -82,7 +82,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
>  	spin_unlock(&wb->list_lock);
>  
>  	global_dirty_limits(&background_thresh, &dirty_thresh);
> -	bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
> +	bdi_thresh = wb_dirty_limit(wb, dirty_thresh);
>  
>  #define K(x) ((x) << (PAGE_SHIFT - 10))
>  	seq_printf(m,
> @@ -106,7 +106,7 @@ static int bdi_debug_stats_show(struct seq_file *m, void *v)
>  		   K(background_thresh),
>  		   (unsigned long) K(wb_stat(wb, WB_DIRTIED)),
>  		   (unsigned long) K(wb_stat(wb, WB_WRITTEN)),
> -		   (unsigned long) K(bdi->write_bandwidth),
> +		   (unsigned long) K(wb->write_bandwidth),
>  		   nr_dirty,
>  		   nr_io,
>  		   nr_more_io,
> @@ -408,6 +408,11 @@ void bdi_unregister(struct backing_dev_info *bdi)
>  }
>  EXPORT_SYMBOL(bdi_unregister);
>  
> +/*
> + * Initial write bandwidth: 100 MB/s
> + */
> +#define INIT_BW		(100 << (20 - PAGE_SHIFT))
> +
>  static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
>  {
>  	int i, err;
> @@ -422,11 +427,22 @@ static int bdi_wb_init(struct bdi_writeback *wb, struct backing_dev_info *bdi)
>  	spin_lock_init(&wb->list_lock);
>  	INIT_DELAYED_WORK(&wb->dwork, bdi_writeback_workfn);
>  
> +	wb->bw_time_stamp = jiffies;
> +	wb->balanced_dirty_ratelimit = INIT_BW;
> +	wb->dirty_ratelimit = INIT_BW;
> +	wb->write_bandwidth = INIT_BW;
> +	wb->avg_write_bandwidth = INIT_BW;
> +
> +	err = fprop_local_init_percpu(&wb->completions, GFP_KERNEL);
> +	if (err)
> +		return err;
> +
>  	for (i = 0; i < NR_WB_STAT_ITEMS; i++) {
>  		err = percpu_counter_init(&wb->stat[i], 0, GFP_KERNEL);
>  		if (err) {
>  			while (--i)
>  				percpu_counter_destroy(&wb->stat[i]);
> +			fprop_local_destroy_percpu(&wb->completions);
>  			return err;
>  		}
>  	}
> @@ -442,12 +458,9 @@ static void bdi_wb_exit(struct bdi_writeback *wb)
>  
>  	for (i = 0; i < NR_WB_STAT_ITEMS; i++)
>  		percpu_counter_destroy(&wb->stat[i]);
> -}
>  
> -/*
> - * Initial write bandwidth: 100 MB/s
> - */
> -#define INIT_BW		(100 << (20 - PAGE_SHIFT))
> +	fprop_local_destroy_percpu(&wb->completions);
> +}
>  
>  int bdi_init(struct backing_dev_info *bdi)
>  {
> @@ -466,22 +479,6 @@ int bdi_init(struct backing_dev_info *bdi)
>  	if (err)
>  		return err;
>  
> -	bdi->dirty_exceeded = 0;
> -
> -	bdi->bw_time_stamp = jiffies;
> -	bdi->written_stamp = 0;
> -
> -	bdi->balanced_dirty_ratelimit = INIT_BW;
> -	bdi->dirty_ratelimit = INIT_BW;
> -	bdi->write_bandwidth = INIT_BW;
> -	bdi->avg_write_bandwidth = INIT_BW;
> -
> -	err = fprop_local_init_percpu(&bdi->completions, GFP_KERNEL);
> -	if (err) {
> -		bdi_wb_exit(&bdi->wb);
> -		return err;
> -	}
> -
>  	return 0;
>  }
>  EXPORT_SYMBOL(bdi_init);
> @@ -514,8 +511,6 @@ void bdi_destroy(struct backing_dev_info *bdi)
>  
>  	bdi_unregister(bdi);
>  	bdi_wb_exit(&bdi->wb);
> -
> -	fprop_local_destroy_percpu(&bdi->completions);
>  }
>  EXPORT_SYMBOL(bdi_destroy);
>  
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 68fd72a..7c721b4 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -399,7 +399,7 @@ static unsigned long wp_next_time(unsigned long cur_time)
>  static inline void __wb_writeout_inc(struct bdi_writeback *wb)
>  {
>  	__inc_wb_stat(wb, WB_WRITTEN);
> -	__fprop_inc_percpu_max(&writeout_completions, &wb->bdi->completions,
> +	__fprop_inc_percpu_max(&writeout_completions, &wb->completions,
>  			       wb->bdi->max_prop_frac);
>  	/* First event after period switching was turned off? */
>  	if (!unlikely(writeout_period_time)) {
> @@ -427,10 +427,10 @@ EXPORT_SYMBOL_GPL(wb_writeout_inc);
>  /*
>   * Obtain an accurate fraction of the BDI's portion.
>   */
> -static void bdi_writeout_fraction(struct backing_dev_info *bdi,
> -		long *numerator, long *denominator)
> +static void wb_writeout_fraction(struct bdi_writeback *wb,
> +				 long *numerator, long *denominator)
>  {
> -	fprop_fraction_percpu(&writeout_completions, &bdi->completions,
> +	fprop_fraction_percpu(&writeout_completions, &wb->completions,
>  				numerator, denominator);
>  }
>  
> @@ -516,11 +516,11 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
>  }
>  
>  /**
> - * bdi_dirty_limit - @bdi's share of dirty throttling threshold
> - * @bdi: the backing_dev_info to query
> + * wb_dirty_limit - @wb's share of dirty throttling threshold
> + * @wb: the bdi_writeback to query
>   * @dirty: global dirty limit in pages
>   *
> - * Returns @bdi's dirty limit in pages. The term "dirty" in the context of
> + * Returns @wb's dirty limit in pages. The term "dirty" in the context of
>   * dirty balancing includes all PG_dirty, PG_writeback and NFS unstable pages.
>   *
>   * Note that balance_dirty_pages() will only seriously take it as a hard limit
> @@ -528,24 +528,25 @@ static unsigned long hard_dirty_limit(unsigned long thresh)
>   * control. For example, when the device is completely stalled due to some error
>   * conditions, or when there are 1000 dd tasks writing to a slow 10MB/s USB key.
>   * In the other normal situations, it acts more gently by throttling the tasks
> - * more (rather than completely block them) when the bdi dirty pages go high.
> + * more (rather than completely block them) when the wb dirty pages go high.
>   *
>   * It allocates high/low dirty limits to fast/slow devices, in order to prevent
>   * - starving fast devices
>   * - piling up dirty pages (that will take long time to sync) on slow devices
>   *
> - * The bdi's share of dirty limit will be adapting to its throughput and
> + * The wb's share of dirty limit will be adapting to its throughput and
>   * bounded by the bdi->min_ratio and/or bdi->max_ratio parameters, if set.
>   */
> -unsigned long bdi_dirty_limit(struct backing_dev_info *bdi, unsigned long dirty)
> +unsigned long wb_dirty_limit(struct bdi_writeback *wb, unsigned long dirty)
>  {
> +	struct backing_dev_info *bdi = wb->bdi;
>  	u64 bdi_dirty;
>  	long numerator, denominator;
>  
>  	/*
>  	 * Calculate this BDI's share of the dirty ratio.
>  	 */
> -	bdi_writeout_fraction(bdi, &numerator, &denominator);
> +	wb_writeout_fraction(wb, &numerator, &denominator);
>  
>  	bdi_dirty = (dirty * (100 - bdi_min_ratio)) / 100;
>  	bdi_dirty *= numerator;
> @@ -664,14 +665,14 @@ static long long pos_ratio_polynom(unsigned long setpoint,
>   *   card's bdi_dirty may rush to many times higher than bdi_setpoint.
>   * - the bdi dirty thresh drops quickly due to change of JBOD workload
>   */
> -static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
> -					unsigned long thresh,
> -					unsigned long bg_thresh,
> -					unsigned long dirty,
> -					unsigned long bdi_thresh,
> -					unsigned long bdi_dirty)
> +static unsigned long wb_position_ratio(struct bdi_writeback *wb,
> +				       unsigned long thresh,
> +				       unsigned long bg_thresh,
> +				       unsigned long dirty,
> +				       unsigned long bdi_thresh,
> +				       unsigned long bdi_dirty)
>  {
> -	unsigned long write_bw = bdi->avg_write_bandwidth;
> +	unsigned long write_bw = wb->avg_write_bandwidth;
>  	unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
>  	unsigned long limit = hard_dirty_limit(thresh);
>  	unsigned long x_intercept;
> @@ -702,12 +703,12 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
>  	 * consume arbitrary amount of RAM because it is accounted in
>  	 * NR_WRITEBACK_TEMP which is not involved in calculating "nr_dirty".
>  	 *
> -	 * Here, in bdi_position_ratio(), we calculate pos_ratio based on
> +	 * Here, in wb_position_ratio(), we calculate pos_ratio based on
>  	 * two values: bdi_dirty and bdi_thresh. Let's consider an example:
>  	 * total amount of RAM is 16GB, bdi->max_ratio is equal to 1%, global
>  	 * limits are set by default to 10% and 20% (background and throttle).
>  	 * Then bdi_thresh is 1% of 20% of 16GB. This amounts to ~8K pages.
> -	 * bdi_dirty_limit(bdi, bg_thresh) is about ~4K pages. bdi_setpoint is
> +	 * wb_dirty_limit(wb, bg_thresh) is about ~4K pages. bdi_setpoint is
>  	 * about ~6K pages (as the average of background and throttle bdi
>  	 * limits). The 3rd order polynomial will provide positive feedback if
>  	 * bdi_dirty is under bdi_setpoint and vice versa.
> @@ -717,7 +718,7 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
>  	 * much earlier than global "freerun" is reached (~23MB vs. ~2.3GB
>  	 * in the example above).
>  	 */
> -	if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
> +	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
>  		long long bdi_pos_ratio;
>  		unsigned long bdi_bg_thresh;
>  
> @@ -842,13 +843,13 @@ static unsigned long bdi_position_ratio(struct backing_dev_info *bdi,
>  	return pos_ratio;
>  }
>  
> -static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
> -				       unsigned long elapsed,
> -				       unsigned long written)
> +static void wb_update_write_bandwidth(struct bdi_writeback *wb,
> +				      unsigned long elapsed,
> +				      unsigned long written)
>  {
>  	const unsigned long period = roundup_pow_of_two(3 * HZ);
> -	unsigned long avg = bdi->avg_write_bandwidth;
> -	unsigned long old = bdi->write_bandwidth;
> +	unsigned long avg = wb->avg_write_bandwidth;
> +	unsigned long old = wb->write_bandwidth;
>  	u64 bw;
>  
>  	/*
> @@ -858,14 +859,14 @@ static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
>  	 * write_bandwidth = ---------------------------------------------------
>  	 *                                          period
>  	 */
> -	bw = written - bdi->written_stamp;
> +	bw = written - wb->written_stamp;
>  	bw *= HZ;
>  	if (unlikely(elapsed > period)) {
>  		do_div(bw, elapsed);
>  		avg = bw;
>  		goto out;
>  	}
> -	bw += (u64)bdi->write_bandwidth * (period - elapsed);
> +	bw += (u64)wb->write_bandwidth * (period - elapsed);
>  	bw >>= ilog2(period);
>  
>  	/*
> @@ -878,8 +879,8 @@ static void bdi_update_write_bandwidth(struct backing_dev_info *bdi,
>  		avg += (old - avg) >> 3;
>  
>  out:
> -	bdi->write_bandwidth = bw;
> -	bdi->avg_write_bandwidth = avg;
> +	wb->write_bandwidth = bw;
> +	wb->avg_write_bandwidth = avg;
>  }
>  
>  /*
> @@ -944,20 +945,20 @@ static void global_update_bandwidth(unsigned long thresh,
>   * Normal bdi tasks will be curbed at or below it in long term.
>   * Obviously it should be around (write_bw / N) when there are N dd tasks.
>   */
> -static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
> -				       unsigned long thresh,
> -				       unsigned long bg_thresh,
> -				       unsigned long dirty,
> -				       unsigned long bdi_thresh,
> -				       unsigned long bdi_dirty,
> -				       unsigned long dirtied,
> -				       unsigned long elapsed)
> +static void wb_update_dirty_ratelimit(struct bdi_writeback *wb,
> +				      unsigned long thresh,
> +				      unsigned long bg_thresh,
> +				      unsigned long dirty,
> +				      unsigned long bdi_thresh,
> +				      unsigned long bdi_dirty,
> +				      unsigned long dirtied,
> +				      unsigned long elapsed)
>  {
>  	unsigned long freerun = dirty_freerun_ceiling(thresh, bg_thresh);
>  	unsigned long limit = hard_dirty_limit(thresh);
>  	unsigned long setpoint = (freerun + limit) / 2;
> -	unsigned long write_bw = bdi->avg_write_bandwidth;
> -	unsigned long dirty_ratelimit = bdi->dirty_ratelimit;
> +	unsigned long write_bw = wb->avg_write_bandwidth;
> +	unsigned long dirty_ratelimit = wb->dirty_ratelimit;
>  	unsigned long dirty_rate;
>  	unsigned long task_ratelimit;
>  	unsigned long balanced_dirty_ratelimit;
> @@ -969,10 +970,10 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
>  	 * The dirty rate will match the writeout rate in long term, except
>  	 * when dirty pages are truncated by userspace or re-dirtied by FS.
>  	 */
> -	dirty_rate = (dirtied - bdi->dirtied_stamp) * HZ / elapsed;
> +	dirty_rate = (dirtied - wb->dirtied_stamp) * HZ / elapsed;
>  
> -	pos_ratio = bdi_position_ratio(bdi, thresh, bg_thresh, dirty,
> -				       bdi_thresh, bdi_dirty);
> +	pos_ratio = wb_position_ratio(wb, thresh, bg_thresh, dirty,
> +				      bdi_thresh, bdi_dirty);
>  	/*
>  	 * task_ratelimit reflects each dd's dirty rate for the past 200ms.
>  	 */
> @@ -1056,31 +1057,31 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
>  
>  	/*
>  	 * For strictlimit case, calculations above were based on bdi counters
> -	 * and limits (starting from pos_ratio = bdi_position_ratio() and up to
> +	 * and limits (starting from pos_ratio = wb_position_ratio() and up to
>  	 * balanced_dirty_ratelimit = task_ratelimit * write_bw / dirty_rate).
>  	 * Hence, to calculate "step" properly, we have to use bdi_dirty as
>  	 * "dirty" and bdi_setpoint as "setpoint".
>  	 *
>  	 * We rampup dirty_ratelimit forcibly if bdi_dirty is low because
>  	 * it's possible that bdi_thresh is close to zero due to inactivity
> -	 * of backing device (see the implementation of bdi_dirty_limit()).
> +	 * of backing device (see the implementation of wb_dirty_limit()).
>  	 */
> -	if (unlikely(bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
> +	if (unlikely(wb->bdi->capabilities & BDI_CAP_STRICTLIMIT)) {
>  		dirty = bdi_dirty;
>  		if (bdi_dirty < 8)
>  			setpoint = bdi_dirty + 1;
>  		else
>  			setpoint = (bdi_thresh +
> -				    bdi_dirty_limit(bdi, bg_thresh)) / 2;
> +				    wb_dirty_limit(wb, bg_thresh)) / 2;
>  	}
>  
>  	if (dirty < setpoint) {
> -		x = min3(bdi->balanced_dirty_ratelimit,
> +		x = min3(wb->balanced_dirty_ratelimit,
>  			 balanced_dirty_ratelimit, task_ratelimit);
>  		if (dirty_ratelimit < x)
>  			step = x - dirty_ratelimit;
>  	} else {
> -		x = max3(bdi->balanced_dirty_ratelimit,
> +		x = max3(wb->balanced_dirty_ratelimit,
>  			 balanced_dirty_ratelimit, task_ratelimit);
>  		if (dirty_ratelimit > x)
>  			step = dirty_ratelimit - x;
> @@ -1102,22 +1103,22 @@ static void bdi_update_dirty_ratelimit(struct backing_dev_info *bdi,
>  	else
>  		dirty_ratelimit -= step;
>  
> -	bdi->dirty_ratelimit = max(dirty_ratelimit, 1UL);
> -	bdi->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
> +	wb->dirty_ratelimit = max(dirty_ratelimit, 1UL);
> +	wb->balanced_dirty_ratelimit = balanced_dirty_ratelimit;
>  
> -	trace_bdi_dirty_ratelimit(bdi, dirty_rate, task_ratelimit);
> +	trace_bdi_dirty_ratelimit(wb->bdi, dirty_rate, task_ratelimit);
>  }
>  
> -void __bdi_update_bandwidth(struct backing_dev_info *bdi,
> -			    unsigned long thresh,
> -			    unsigned long bg_thresh,
> -			    unsigned long dirty,
> -			    unsigned long bdi_thresh,
> -			    unsigned long bdi_dirty,
> -			    unsigned long start_time)
> +void __wb_update_bandwidth(struct bdi_writeback *wb,
> +			   unsigned long thresh,
> +			   unsigned long bg_thresh,
> +			   unsigned long dirty,
> +			   unsigned long bdi_thresh,
> +			   unsigned long bdi_dirty,
> +			   unsigned long start_time)
>  {
>  	unsigned long now = jiffies;
> -	unsigned long elapsed = now - bdi->bw_time_stamp;
> +	unsigned long elapsed = now - wb->bw_time_stamp;
>  	unsigned long dirtied;
>  	unsigned long written;
>  
> @@ -1127,44 +1128,44 @@ void __bdi_update_bandwidth(struct backing_dev_info *bdi,
>  	if (elapsed < BANDWIDTH_INTERVAL)
>  		return;
>  
> -	dirtied = percpu_counter_read(&bdi->wb.stat[WB_DIRTIED]);
> -	written = percpu_counter_read(&bdi->wb.stat[WB_WRITTEN]);
> +	dirtied = percpu_counter_read(&wb->stat[WB_DIRTIED]);
> +	written = percpu_counter_read(&wb->stat[WB_WRITTEN]);
>  
>  	/*
>  	 * Skip quiet periods when disk bandwidth is under-utilized.
>  	 * (at least 1s idle time between two flusher runs)
>  	 */
> -	if (elapsed > HZ && time_before(bdi->bw_time_stamp, start_time))
> +	if (elapsed > HZ && time_before(wb->bw_time_stamp, start_time))
>  		goto snapshot;
>  
>  	if (thresh) {
>  		global_update_bandwidth(thresh, dirty, now);
> -		bdi_update_dirty_ratelimit(bdi, thresh, bg_thresh, dirty,
> -					   bdi_thresh, bdi_dirty,
> -					   dirtied, elapsed);
> +		wb_update_dirty_ratelimit(wb, thresh, bg_thresh, dirty,
> +					  bdi_thresh, bdi_dirty,
> +					  dirtied, elapsed);
>  	}
> -	bdi_update_write_bandwidth(bdi, elapsed, written);
> +	wb_update_write_bandwidth(wb, elapsed, written);
>  
>  snapshot:
> -	bdi->dirtied_stamp = dirtied;
> -	bdi->written_stamp = written;
> -	bdi->bw_time_stamp = now;
> +	wb->dirtied_stamp = dirtied;
> +	wb->written_stamp = written;
> +	wb->bw_time_stamp = now;
>  }
>  
> -static void bdi_update_bandwidth(struct backing_dev_info *bdi,
> -				 unsigned long thresh,
> -				 unsigned long bg_thresh,
> -				 unsigned long dirty,
> -				 unsigned long bdi_thresh,
> -				 unsigned long bdi_dirty,
> -				 unsigned long start_time)
> +static void wb_update_bandwidth(struct bdi_writeback *wb,
> +				unsigned long thresh,
> +				unsigned long bg_thresh,
> +				unsigned long dirty,
> +				unsigned long bdi_thresh,
> +				unsigned long bdi_dirty,
> +				unsigned long start_time)
>  {
> -	if (time_is_after_eq_jiffies(bdi->bw_time_stamp + BANDWIDTH_INTERVAL))
> +	if (time_is_after_eq_jiffies(wb->bw_time_stamp + BANDWIDTH_INTERVAL))
>  		return;
> -	spin_lock(&bdi->wb.list_lock);
> -	__bdi_update_bandwidth(bdi, thresh, bg_thresh, dirty,
> -			       bdi_thresh, bdi_dirty, start_time);
> -	spin_unlock(&bdi->wb.list_lock);
> +	spin_lock(&wb->list_lock);
> +	__wb_update_bandwidth(wb, thresh, bg_thresh, dirty,
> +			      bdi_thresh, bdi_dirty, start_time);
> +	spin_unlock(&wb->list_lock);
>  }
>  
>  /*
> @@ -1184,10 +1185,10 @@ static unsigned long dirty_poll_interval(unsigned long dirty,
>  	return 1;
>  }
>  
> -static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
> -				   unsigned long bdi_dirty)
> +static unsigned long wb_max_pause(struct bdi_writeback *wb,
> +				      unsigned long bdi_dirty)
>  {
> -	unsigned long bw = bdi->avg_write_bandwidth;
> +	unsigned long bw = wb->avg_write_bandwidth;
>  	unsigned long t;
>  
>  	/*
> @@ -1203,14 +1204,14 @@ static unsigned long bdi_max_pause(struct backing_dev_info *bdi,
>  	return min_t(unsigned long, t, MAX_PAUSE);
>  }
>  
> -static long bdi_min_pause(struct backing_dev_info *bdi,
> -			  long max_pause,
> -			  unsigned long task_ratelimit,
> -			  unsigned long dirty_ratelimit,
> -			  int *nr_dirtied_pause)
> +static long wb_min_pause(struct bdi_writeback *wb,
> +			 long max_pause,
> +			 unsigned long task_ratelimit,
> +			 unsigned long dirty_ratelimit,
> +			 int *nr_dirtied_pause)
>  {
> -	long hi = ilog2(bdi->avg_write_bandwidth);
> -	long lo = ilog2(bdi->dirty_ratelimit);
> +	long hi = ilog2(wb->avg_write_bandwidth);
> +	long lo = ilog2(wb->dirty_ratelimit);
>  	long t;		/* target pause */
>  	long pause;	/* estimated next pause */
>  	int pages;	/* target nr_dirtied_pause */
> @@ -1278,14 +1279,13 @@ static long bdi_min_pause(struct backing_dev_info *bdi,
>  	return pages >= DIRTY_POLL_THRESH ? 1 + t / 2 : t;
>  }
>  
> -static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
> -				    unsigned long dirty_thresh,
> -				    unsigned long background_thresh,
> -				    unsigned long *bdi_dirty,
> -				    unsigned long *bdi_thresh,
> -				    unsigned long *bdi_bg_thresh)
> +static inline void wb_dirty_limits(struct bdi_writeback *wb,
> +				   unsigned long dirty_thresh,
> +				   unsigned long background_thresh,
> +				   unsigned long *bdi_dirty,
> +				   unsigned long *bdi_thresh,
> +				   unsigned long *bdi_bg_thresh)
>  {
> -	struct bdi_writeback *wb = &bdi->wb;
>  	unsigned long wb_reclaimable;
>  
>  	/*
> @@ -1298,10 +1298,10 @@ static inline void bdi_dirty_limits(struct backing_dev_info *bdi,
>  	 *   In this case we don't want to hard throttle the USB key
>  	 *   dirtiers for 100 seconds until bdi_dirty drops under
>  	 *   bdi_thresh. Instead the auxiliary bdi control line in
> -	 *   bdi_position_ratio() will let the dirtier task progress
> +	 *   wb_position_ratio() will let the dirtier task progress
>  	 *   at some rate <= (write_bw / 2) for bringing down bdi_dirty.
>  	 */
> -	*bdi_thresh = bdi_dirty_limit(bdi, dirty_thresh);
> +	*bdi_thresh = wb_dirty_limit(wb, dirty_thresh);
>  
>  	if (bdi_bg_thresh)
>  		*bdi_bg_thresh = dirty_thresh ? div_u64((u64)*bdi_thresh *
> @@ -1351,6 +1351,7 @@ static void balance_dirty_pages(struct address_space *mapping,
>  	unsigned long dirty_ratelimit;
>  	unsigned long pos_ratio;
>  	struct backing_dev_info *bdi = mapping->backing_dev_info;
> +	struct bdi_writeback *wb = &bdi->wb;
>  	bool strictlimit = bdi->capabilities & BDI_CAP_STRICTLIMIT;
>  	unsigned long start_time = jiffies;
>  
> @@ -1375,8 +1376,8 @@ static void balance_dirty_pages(struct address_space *mapping,
>  		global_dirty_limits(&background_thresh, &dirty_thresh);
>  
>  		if (unlikely(strictlimit)) {
> -			bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
> -					 &bdi_dirty, &bdi_thresh, &bg_thresh);
> +			wb_dirty_limits(wb, dirty_thresh, background_thresh,
> +					&bdi_dirty, &bdi_thresh, &bg_thresh);
>  
>  			dirty = bdi_dirty;
>  			thresh = bdi_thresh;
> @@ -1407,28 +1408,28 @@ static void balance_dirty_pages(struct address_space *mapping,
>  			bdi_start_background_writeback(bdi);
>  
>  		if (!strictlimit)
> -			bdi_dirty_limits(bdi, dirty_thresh, background_thresh,
> -					 &bdi_dirty, &bdi_thresh, NULL);
> +			wb_dirty_limits(wb, dirty_thresh, background_thresh,
> +					&bdi_dirty, &bdi_thresh, NULL);
>  
>  		dirty_exceeded = (bdi_dirty > bdi_thresh) &&
>  				 ((nr_dirty > dirty_thresh) || strictlimit);
> -		if (dirty_exceeded && !bdi->dirty_exceeded)
> -			bdi->dirty_exceeded = 1;
> +		if (dirty_exceeded && !wb->dirty_exceeded)
> +			wb->dirty_exceeded = 1;
>  
> -		bdi_update_bandwidth(bdi, dirty_thresh, background_thresh,
> -				     nr_dirty, bdi_thresh, bdi_dirty,
> -				     start_time);
> +		wb_update_bandwidth(wb, dirty_thresh, background_thresh,
> +				    nr_dirty, bdi_thresh, bdi_dirty,
> +				    start_time);
>  
> -		dirty_ratelimit = bdi->dirty_ratelimit;
> -		pos_ratio = bdi_position_ratio(bdi, dirty_thresh,
> -					       background_thresh, nr_dirty,
> -					       bdi_thresh, bdi_dirty);
> +		dirty_ratelimit = wb->dirty_ratelimit;
> +		pos_ratio = wb_position_ratio(wb, dirty_thresh,
> +					      background_thresh, nr_dirty,
> +					      bdi_thresh, bdi_dirty);
>  		task_ratelimit = ((u64)dirty_ratelimit * pos_ratio) >>
>  							RATELIMIT_CALC_SHIFT;
> -		max_pause = bdi_max_pause(bdi, bdi_dirty);
> -		min_pause = bdi_min_pause(bdi, max_pause,
> -					  task_ratelimit, dirty_ratelimit,
> -					  &nr_dirtied_pause);
> +		max_pause = wb_max_pause(wb, bdi_dirty);
> +		min_pause = wb_min_pause(wb, max_pause,
> +					 task_ratelimit, dirty_ratelimit,
> +					 &nr_dirtied_pause);
>  
>  		if (unlikely(task_ratelimit == 0)) {
>  			period = max_pause;
> @@ -1512,15 +1513,15 @@ pause:
>  		 * more page. However bdi_dirty has accounting errors.  So use
>  		 * the larger and more IO friendly wb_stat_error.
>  		 */
> -		if (bdi_dirty <= wb_stat_error(&bdi->wb))
> +		if (bdi_dirty <= wb_stat_error(wb))
>  			break;
>  
>  		if (fatal_signal_pending(current))
>  			break;
>  	}
>  
> -	if (!dirty_exceeded && bdi->dirty_exceeded)
> -		bdi->dirty_exceeded = 0;
> +	if (!dirty_exceeded && wb->dirty_exceeded)
> +		wb->dirty_exceeded = 0;
>  
>  	if (writeback_in_progress(bdi))
>  		return;
> @@ -1584,6 +1585,7 @@ DEFINE_PER_CPU(int, dirty_throttle_leaks) = 0;
>  void balance_dirty_pages_ratelimited(struct address_space *mapping)
>  {
>  	struct backing_dev_info *bdi = mapping->backing_dev_info;
> +	struct bdi_writeback *wb = &bdi->wb;
>  	int ratelimit;
>  	int *p;
>  
> @@ -1591,7 +1593,7 @@ void balance_dirty_pages_ratelimited(struct address_space *mapping)
>  		return;
>  
>  	ratelimit = current->nr_dirtied_pause;
> -	if (bdi->dirty_exceeded)
> +	if (wb->dirty_exceeded)
>  		ratelimit = min(ratelimit, 32 >> (PAGE_SHIFT - 10));
>  
>  	preempt_disable();
> -- 
> 1.9.3
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR