linux-kernel - Re: [PATCH] mm: Make logic in bdi_forker

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Message-ID: <20110902113000.GE12182@quack.suse.cz>
Date:	Fri, 2 Sep 2011 13:30:00 +0200
From:	Jan Kara <jack@...e.cz>
To:	Jens Axboe <jaxboe@...ionio.com>
Cc:	LKML <linux-kernel@...r.kernel.org>, linux-mm@...ck.org,
	Jan Kara <jack@...e.cz>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Wu Fengguang <fengguang.wu@...el.com>, consul.kautuk@...il.com
Subject: Re: [PATCH] mm: Make logic in bdi_forker_thread() straight

On Fri 02-09-11 13:26:08, Jan Kara wrote:
> The logic in bdi_forker_thread() is unnecessarily convoluted by setting task
> state there and back or calling schedule_timeout() in TASK_RUNNING state. Also
> clearing of BDI_pending bit is placed at the and of global loop and cases of a
> switch which mustn't reach it must call 'continue' instead of 'break' which is
> non-intuitive and thus asking for trouble. So make the logic more obvious.
> 
> CC: Andrew Morton <akpm@...ux-foundation.org>
> CC: Wu Fengguang <fengguang.wu@...el.com>
> CC: consul.kautuk@...il.com
> Signed-off-by: Jan Kara <jack@...e.cz>
  Argh, this patch is missing one fix I forgot to commit --amend to it. I'm
sending v2 in a minute. Sorry for the noise.

									Honza
> ---
>  mm/backing-dev.c |   37 ++++++++++++++++++++-----------------
>  1 files changed, 20 insertions(+), 17 deletions(-)
> 
>  Jens, would you merge this patch?
> 
> diff --git a/mm/backing-dev.c b/mm/backing-dev.c
> index d6edf8d..fc441d7 100644
> --- a/mm/backing-dev.c
> +++ b/mm/backing-dev.c
> @@ -359,6 +359,17 @@ static unsigned long bdi_longest_inactive(void)
>  	return max(5UL * 60 * HZ, interval);
>  }
>  
> +/*
> + * Clear pending bit and wakeup anybody waiting for flusher thread startup
> + * or teardown.
> + */
> +static void bdi_clear_pending(struct backing_dev *bdi)
> +{
> +	clear_bit(BDI_pending, &bdi->state);
> +	smp_mb__after_clear_bit();
> +	wake_up_bit(&bdi->state, BDI_pending);
> +}
> +
>  static int bdi_forker_thread(void *ptr)
>  {
>  	struct bdi_writeback *me = ptr;
> @@ -390,8 +401,6 @@ static int bdi_forker_thread(void *ptr)
>  		}
>  
>  		spin_lock_bh(&bdi_lock);
> -		set_current_state(TASK_INTERRUPTIBLE);
> -
>  		list_for_each_entry(bdi, &bdi_list, bdi_list) {
>  			bool have_dirty_io;
>  
> @@ -441,13 +450,8 @@ static int bdi_forker_thread(void *ptr)
>  		}
>  		spin_unlock_bh(&bdi_lock);
>  
> -		/* Keep working if default bdi still has things to do */
> -		if (!list_empty(&me->bdi->work_list))
> -			__set_current_state(TASK_RUNNING);
> -
>  		switch (action) {
>  		case FORK_THREAD:
> -			__set_current_state(TASK_RUNNING);
>  			task = kthread_create(bdi_writeback_thread, &bdi->wb,
>  					      "flush-%s", dev_name(bdi->dev));
>  			if (IS_ERR(task)) {
> @@ -469,14 +473,21 @@ static int bdi_forker_thread(void *ptr)
>  				spin_unlock_bh(&bdi->wb_lock);
>  				wake_up_process(task);
>  			}
> +			bdi_clear_pending(bdi);
>  			break;
>  
>  		case KILL_THREAD:
> -			__set_current_state(TASK_RUNNING);
>  			kthread_stop(task);
> +			bdi_clear_pending(bdi);
>  			break;
>  
>  		case NO_ACTION:
> +			/* Keep working if default bdi still has things to do */
> +			if (!list_empty(&me->bdi->work_list)) {
> +				try_to_freeze();
> +				break;
> +			}
> +			set_current_state(TASK_INTERRUPTIBLE);
>  			if (!wb_has_dirty_io(me) || !dirty_writeback_interval)
>  				/*
>  				 * There are no dirty data. The only thing we
> @@ -489,16 +500,8 @@ static int bdi_forker_thread(void *ptr)
>  			else
>  				schedule_timeout(msecs_to_jiffies(dirty_writeback_interval * 10));
>  			try_to_freeze();
> -			/* Back to the main loop */
> -			continue;
> +			break;
>  		}
> -
> -		/*
> -		 * Clear pending bit and wakeup anybody waiting to tear us down.
> -		 */
> -		clear_bit(BDI_pending, &bdi->state);
> -		smp_mb__after_clear_bit();
> -		wake_up_bit(&bdi->state, BDI_pending);
>  	}
>  
>  	return 0;
> -- 
> 1.7.1
> 
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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