linux-kernel - Re: [PATCH 5/7] writeback: inline allocation failure handling in bdi_alloc_queue

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Date:	Mon, 14 Sep 2009 15:13:42 +0200
From:	Jan Kara <jack@...e.cz>
To:	Jens Axboe <jens.axboe@...cle.com>
Cc:	linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	chris.mason@...cle.com, hch@...radead.org, tytso@....edu,
	akpm@...ux-foundation.org, jack@...e.cz, trond.myklebust@....uio.no
Subject: Re: [PATCH 5/7] writeback: inline allocation failure handling in
	bdi_alloc_queue_work()

On Mon 14-09-09 11:36:32, Jens Axboe wrote:
> This gets rid of work == NULL in bdi_queue_work() and puts the
> OOM handling where it belongs.
  Looks good.

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

								Honza
> 
> Signed-off-by: Jens Axboe <jens.axboe@...cle.com>
> ---
>  fs/fs-writeback.c |   55 +++++++++++++++++++++++++++-------------------------
>  1 files changed, 29 insertions(+), 26 deletions(-)
> 
> diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
> index d7592c7..5cd8b3b 100644
> --- a/fs/fs-writeback.c
> +++ b/fs/fs-writeback.c
> @@ -139,21 +139,19 @@ static void wb_clear_pending(struct bdi_writeback *wb, struct bdi_work *work)
>  
>  static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
>  {
> -	if (work) {
> -		work->seen = bdi->wb_mask;
> -		BUG_ON(!work->seen);
> -		atomic_set(&work->pending, bdi->wb_cnt);
> -		BUG_ON(!bdi->wb_cnt);
> +	work->seen = bdi->wb_mask;
> +	BUG_ON(!work->seen);
> +	atomic_set(&work->pending, bdi->wb_cnt);
> +	BUG_ON(!bdi->wb_cnt);
>  
> -		/*
> -		 * Make sure stores are seen before it appears on the list
> -		 */
> -		smp_mb();
> +	/*
> +	 * Make sure stores are seen before it appears on the list
> +	 */
> +	smp_mb();
>  
> -		spin_lock(&bdi->wb_lock);
> -		list_add_tail_rcu(&work->list, &bdi->work_list);
> -		spin_unlock(&bdi->wb_lock);
> -	}
> +	spin_lock(&bdi->wb_lock);
> +	list_add_tail_rcu(&work->list, &bdi->work_list);
> +	spin_unlock(&bdi->wb_lock);
>  
>  	/*
>  	 * If the default thread isn't there, make sure we add it. When
> @@ -165,14 +163,12 @@ static void bdi_queue_work(struct backing_dev_info *bdi, struct bdi_work *work)
>  		struct bdi_writeback *wb = &bdi->wb;
>  
>  		/*
> -		 * If we failed allocating the bdi work item, wake up the wb
> -		 * thread always. As a safety precaution, it'll flush out
> -		 * everything
> +		 * End work now if this wb has no dirty IO pending. Otherwise
> +		 * wakeup the handling thread
>  		 */
> -		if (!wb_has_dirty_io(wb)) {
> -			if (work)
> -				wb_clear_pending(wb, work);
> -		} else if (wb->task)
> +		if (!wb_has_dirty_io(wb))
> +			wb_clear_pending(wb, work);
> +		else if (wb->task)
>  			wake_up_process(wb->task);
>  	}
>  }
> @@ -192,11 +188,20 @@ static void bdi_alloc_queue_work(struct backing_dev_info *bdi,
>  {
>  	struct bdi_work *work;
>  
> +	/*
> +	 * This is WB_SYNC_NONE writeback, so if allocation fails just
> +	 * wakeup the thread for old dirty data writeback
> +	 */
>  	work = kmalloc(sizeof(*work), GFP_ATOMIC);
> -	if (work)
> +	if (work) {
>  		bdi_work_init(work, wbc);
> +		bdi_queue_work(bdi, work);
> +	} else {
> +		struct bdi_writeback *wb = &bdi->wb;
>  
> -	bdi_queue_work(bdi, work);
> +		if (wb->task)
> +			wake_up_process(wb->task);
> +	}
>  }
>  
>  void bdi_start_writeback(struct writeback_control *wbc)
> @@ -852,10 +857,8 @@ static void bdi_writeback_all(struct writeback_control *wbc)
>  	rcu_read_lock();
>  
>  	list_for_each_entry(bdi, &bdi_list, bdi_list) {
> -		if (!bdi_has_dirty_io(bdi))
> -			continue;
> -
> -		bdi_alloc_queue_work(bdi, wbc);
> +		if (bdi_has_dirty_io(bdi))
> +			bdi_alloc_queue_work(bdi, wbc);
>  	}
>  
>  	rcu_read_unlock();
> -- 
> 1.6.4.1.207.g68ea
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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