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Date:   Fri, 22 Sep 2017 15:17:01 +0200
From:   Jan Kara <jack@...e.cz>
To:     Jens Axboe <axboe@...nel.dk>
Cc:     linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        linux-mm@...ck.org, hannes@...xchg.org, clm@...com, jack@...e.cz
Subject: Re: [PATCH 6/7] fs-writeback: move nr_pages == 0 logic to one
 location

On Wed 20-09-17 09:33:01, Jens Axboe wrote:
> Now that we have no external callers of wb_start_writeback(), we
> can shuffle the passing in of 'nr_pages'. Everybody passes in 0
> at this point, so just kill the argument and move the dirty
> count retrieval to that function.
> 
> Acked-by: Johannes Weiner <hannes@...xchg.org>
> Tested-by: Chris Mason <clm@...com>
> Signed-off-by: Jens Axboe <axboe@...nel.dk>

Looks good. You can add:

Reviewed-by: Jan Kara <jack@...e.cz>

										Honza

> ---
>  fs/fs-writeback.c | 42 ++++++++++++++++++------------------------
>  1 file changed, 18 insertions(+), 24 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index ecbd26d1121d..3916ea2484ae 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -933,8 +933,19 @@ static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
>  
>  #endif	/* CONFIG_CGROUP_WRITEBACK */
>  
> -static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
> -			       bool range_cyclic, enum wb_reason reason)
> +/*
> + * Add in the number of potentially dirty inodes, because each inode
> + * write can dirty pagecache in the underlying blockdev.
> + */
> +static unsigned long get_nr_dirty_pages(void)
> +{
> +	return global_node_page_state(NR_FILE_DIRTY) +
> +		global_node_page_state(NR_UNSTABLE_NFS) +
> +		get_nr_dirty_inodes();
> +}
> +
> +static void wb_start_writeback(struct bdi_writeback *wb, bool range_cyclic,
> +			       enum wb_reason reason)
>  {
>  	struct wb_writeback_work *work;
>  
> @@ -954,7 +965,7 @@ static void wb_start_writeback(struct bdi_writeback *wb, long nr_pages,
>  	}
>  
>  	work->sync_mode	= WB_SYNC_NONE;
> -	work->nr_pages	= nr_pages;
> +	work->nr_pages	= wb_split_bdi_pages(wb, get_nr_dirty_pages());
>  	work->range_cyclic = range_cyclic;
>  	work->reason	= reason;
>  	work->auto_free	= 1;
> @@ -1814,17 +1825,6 @@ static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
>  	return work;
>  }
>  
> -/*
> - * Add in the number of potentially dirty inodes, because each inode
> - * write can dirty pagecache in the underlying blockdev.
> - */
> -static unsigned long get_nr_dirty_pages(void)
> -{
> -	return global_node_page_state(NR_FILE_DIRTY) +
> -		global_node_page_state(NR_UNSTABLE_NFS) +
> -		get_nr_dirty_inodes();
> -}
> -
>  static long wb_check_background_flush(struct bdi_writeback *wb)
>  {
>  	if (wb_over_bg_thresh(wb)) {
> @@ -1951,7 +1951,7 @@ void wb_workfn(struct work_struct *work)
>   * write back the whole world.
>   */
>  static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
> -					 long nr_pages, enum wb_reason reason)
> +					 enum wb_reason reason)
>  {
>  	struct bdi_writeback *wb;
>  
> @@ -1959,17 +1959,14 @@ static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
>  		return;
>  
>  	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
> -		wb_start_writeback(wb, wb_split_bdi_pages(wb, nr_pages),
> -					   false, reason);
> +		wb_start_writeback(wb, false, reason);
>  }
>  
>  void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
>  				enum wb_reason reason)
>  {
> -	long nr_pages = get_nr_dirty_pages();
> -
>  	rcu_read_lock();
> -	__wakeup_flusher_threads_bdi(bdi, nr_pages, reason);
> +	__wakeup_flusher_threads_bdi(bdi, reason);
>  	rcu_read_unlock();
>  }
>  
> @@ -1979,7 +1976,6 @@ void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
>  void wakeup_flusher_threads(enum wb_reason reason)
>  {
>  	struct backing_dev_info *bdi;
> -	long nr_pages;
>  
>  	/*
>  	 * If we are expecting writeback progress we must submit plugged IO.
> @@ -1987,11 +1983,9 @@ void wakeup_flusher_threads(enum wb_reason reason)
>  	if (blk_needs_flush_plug(current))
>  		blk_schedule_flush_plug(current);
>  
> -	nr_pages = get_nr_dirty_pages();
> -
>  	rcu_read_lock();
>  	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
> -		__wakeup_flusher_threads_bdi(bdi, nr_pages, reason);
> +		__wakeup_flusher_threads_bdi(bdi, reason);
>  	rcu_read_unlock();
>  }
>  
> -- 
> 2.7.4
> 
-- 
Jan Kara <jack@...e.com>
SUSE Labs, CR

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