[PATCH] mm: Make logic in bdi_forker_thread() straight

[PATCH] mm: Make logic in bdi_forker_thread() straight

[Jan Kara]

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@linux-foundation.org>
CC: Wu Fengguang <fengguang.wu@intel.com>
CC: consul.kautuk@gmail.com
Signed-off-by: Jan Kara <jack@suse.cz>
---
 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

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Re: [PATCH] mm: Make logic in bdi_forker_thread() straight

[Jan Kara]

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@linux-foundation.org>
> CC: Wu Fengguang <fengguang.wu@intel.com>
> CC: consul.kautuk@gmail.com
> Signed-off-by: Jan Kara <jack@suse.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@suse.cz>
SUSE Labs, CR

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