Re: [PATCH 3/7] writeback: only use bdi_writeback_all() for WB_SYNC_NONE writeout

[Jan Kara <jack@suse.cz>]

On Mon 14-09-09 11:36:30, Jens Axboe wrote:
> Data integrity writeback must use bdi_start_writeback() and ensure
> that wbc->sb and wbc->bdi are set.
  This patch looks good.
Acked-by: Jan Kara <jack@suse.cz>

								Honza

> 
> Signed-off-by: Jens Axboe <jens.axboe@oracle.com>
> ---
>  fs/fs-writeback.c |   69 ++++++++++------------------------------------------
>  1 files changed, 14 insertions(+), 55 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index 1873fd0..5d4bd1c 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -187,7 +187,8 @@ static void bdi_wait_on_work_clear(struct bdi_work *work)
>  		    TASK_UNINTERRUPTIBLE);
>  }
>  
> -static struct bdi_work *bdi_alloc_work(struct writeback_control *wbc)
> +static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
> +				 struct writeback_control *wbc)
>  {
>  	struct bdi_work *work;
>  
> @@ -195,7 +196,7 @@ static struct bdi_work *bdi_alloc_work(struct writeback_control *wbc)
>  	if (work)
>  		bdi_work_init(work, wbc);
>  
> -	return work;
> +	bdi_queue_work(bdi, work);
>  }
>  
>  void bdi_start_writeback(struct writeback_control *wbc)
> @@ -205,11 +206,9 @@ void bdi_start_writeback(struct writeback_control *wbc)
>  	 * bdi_queue_work() will wake up the thread and flush old data. This
>  	 * should ensure some amount of progress in freeing memory.
>  	 */
> -	if (wbc->sync_mode != WB_SYNC_ALL) {
> -		struct bdi_work *w = bdi_alloc_work(wbc);
> -
> -		bdi_queue_work(wbc->bdi, w);
> -	} else {
> +	if (wbc->sync_mode != WB_SYNC_ALL)
> +		bdi_alloc_queue_work(wbc->bdi, wbc);
> +	else {
>  		struct bdi_work work;
>  
>  		bdi_work_init(&work, wbc);
> @@ -840,67 +839,26 @@ int bdi_writeback_task(struct bdi_writeback *wb)
>  }
>  
>  /*
> - * Schedule writeback for all backing devices. Expensive! If this is a data
> - * integrity operation, writeback will be complete when this returns. If
> - * we are simply called for WB_SYNC_NONE, then writeback will merely be
> - * scheduled to run.
> + * Schedule writeback for all backing devices. Can only be used for
> + * WB_SYNC_NONE writeback, WB_SYNC_ALL should use bdi_start_writeback()
> + * and pass in the superblock.
>   */
>  static void bdi_writeback_all(struct writeback_control *wbc)
>  {
> -	const bool must_wait = wbc->sync_mode == WB_SYNC_ALL;
>  	struct backing_dev_info *bdi;
> -	struct bdi_work *work;
> -	LIST_HEAD(list);
>  
> -restart:
> +	WARN_ON(wbc->sync_mode == WB_SYNC_ALL);
> +
>  	spin_lock(&bdi_lock);
>  
>  	list_for_each_entry(bdi, &bdi_list, bdi_list) {
> -		struct bdi_work *work;
> -
>  		if (!bdi_has_dirty_io(bdi))
>  			continue;
>  
> -		/*
> -		 * If work allocation fails, do the writes inline. We drop
> -		 * the lock and restart the list writeout. This should be OK,
> -		 * since this happens rarely and because the writeout should
> -		 * eventually make more free memory available.
> -		 */
> -		work = bdi_alloc_work(wbc);
> -		if (!work) {
> -			struct writeback_control __wbc;
> -
> -			/*
> -			 * Not a data integrity writeout, just continue
> -			 */
> -			if (!must_wait)
> -				continue;
> -
> -			spin_unlock(&bdi_lock);
> -			__wbc = *wbc;
> -			__wbc.bdi = bdi;
> -			writeback_inodes_wbc(&__wbc);
> -			goto restart;
> -		}
> -		if (must_wait)
> -			list_add_tail(&work->wait_list, &list);
> -
> -		bdi_queue_work(bdi, work);
> +		bdi_alloc_queue_work(bdi, wbc);
>  	}
>  
>  	spin_unlock(&bdi_lock);
> -
> -	/*
> -	 * If this is for WB_SYNC_ALL, wait for pending work to complete
> -	 * before returning.
> -	 */
> -	while (!list_empty(&list)) {
> -		work = list_entry(list.next, struct bdi_work, wait_list);
> -		list_del(&work->wait_list);
> -		bdi_wait_on_work_clear(work);
> -		call_rcu(&work->rcu_head, bdi_work_free);
> -	}
>  }
>  
>  /*
> @@ -1157,6 +1115,7 @@ long sync_inodes_sb(struct super_block *sb)
>  {
>  	struct writeback_control wbc = {
>  		.sb		= sb,
> +		.bdi		= sb->s_bdi,
>  		.sync_mode	= WB_SYNC_ALL,
>  		.range_start	= 0,
>  		.range_end	= LLONG_MAX,
> @@ -1164,7 +1123,7 @@ long sync_inodes_sb(struct super_block *sb)
>  	long nr_to_write = LONG_MAX; /* doesn't actually matter */
>  
>  	wbc.nr_to_write = nr_to_write;
> -	bdi_writeback_all(&wbc);
> +	bdi_start_writeback(&wbc);
>  	wait_sb_inodes(&wbc);
>  	return nr_to_write - wbc.nr_to_write;
>  }
> -- 
> 1.6.4.1.207.g68ea
> 
-- 
Jan Kara <jack@suse.cz>
SUSE Labs, CR