diff mbox

[4/9] writeback: track if we're sleeping on progress in balance_dirty_pages()

Message ID 1459350477-16404-5-git-send-email-axboe@fb.com (mailing list archive)
State New, archived
Headers show

Commit Message

Jens Axboe March 30, 2016, 3:07 p.m. UTC
Note in the bdi_writeback structure if a task is currently being
limited in balance_dirty_pages(), waiting for writeback to
proceed.

Signed-off-by: Jens Axboe <axboe@fb.com>
---
 include/linux/backing-dev-defs.h | 2 ++
 mm/page-writeback.c              | 2 ++
 2 files changed, 4 insertions(+)

Comments

Jan Kara April 13, 2016, 1:08 p.m. UTC | #1
On Wed 30-03-16 09:07:52, Jens Axboe wrote:
> Note in the bdi_writeback structure if a task is currently being
> limited in balance_dirty_pages(), waiting for writeback to
> proceed.
...
> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
> index 11ff8f758631..15e696bc5d14 100644
> --- a/mm/page-writeback.c
> +++ b/mm/page-writeback.c
> @@ -1746,7 +1746,9 @@ pause:
>  					  pause,
>  					  start_time);
>  		__set_current_state(TASK_KILLABLE);
> +		wb->dirty_sleeping = 1;
>  		io_schedule_timeout(pause);
> +		wb->dirty_sleeping = 0;

Huh, but wb->dirty_sleeping is shared by all the processes in the system.
So this is seriously racy, isn't it? You rather need a counter for this to
work.

								Honza
Jens Axboe April 13, 2016, 2:20 p.m. UTC | #2
On 04/13/2016 07:08 AM, Jan Kara wrote:
> On Wed 30-03-16 09:07:52, Jens Axboe wrote:
>> Note in the bdi_writeback structure if a task is currently being
>> limited in balance_dirty_pages(), waiting for writeback to
>> proceed.
> ...
>> diff --git a/mm/page-writeback.c b/mm/page-writeback.c
>> index 11ff8f758631..15e696bc5d14 100644
>> --- a/mm/page-writeback.c
>> +++ b/mm/page-writeback.c
>> @@ -1746,7 +1746,9 @@ pause:
>>   					  pause,
>>   					  start_time);
>>   		__set_current_state(TASK_KILLABLE);
>> +		wb->dirty_sleeping = 1;
>>   		io_schedule_timeout(pause);
>> +		wb->dirty_sleeping = 0;
>
> Huh, but wb->dirty_sleeping is shared by all the processes in the system.
> So this is seriously racy, isn't it? You rather need a counter for this to
> work.

Sure, but it's not _that_ important. It's like wb->dirty_exceeded, we 
have an equally relaxed relationship.

I don't mind making it more solid, but I can't make it a counter without 
making it atomic. Which is why I left it as just a basic assignment. But 
I guess since we only fiddle with it when going to sleep, we can make it 
an atomic and not have to worry about the potential impact.
diff mbox

Patch

diff --git a/include/linux/backing-dev-defs.h b/include/linux/backing-dev-defs.h
index 1b4d69f68c33..f702309216b4 100644
--- a/include/linux/backing-dev-defs.h
+++ b/include/linux/backing-dev-defs.h
@@ -116,6 +116,8 @@  struct bdi_writeback {
 	struct list_head work_list;
 	struct delayed_work dwork;	/* work item used for writeback */
 
+	int dirty_sleeping;		/* waiting on dirty limit exceeded */
+
 	struct list_head bdi_node;	/* anchored at bdi->wb_list */
 
 #ifdef CONFIG_CGROUP_WRITEBACK
diff --git a/mm/page-writeback.c b/mm/page-writeback.c
index 11ff8f758631..15e696bc5d14 100644
--- a/mm/page-writeback.c
+++ b/mm/page-writeback.c
@@ -1746,7 +1746,9 @@  pause:
 					  pause,
 					  start_time);
 		__set_current_state(TASK_KILLABLE);
+		wb->dirty_sleeping = 1;
 		io_schedule_timeout(pause);
+		wb->dirty_sleeping = 0;
 
 		current->dirty_paused_when = now + pause;
 		current->nr_dirtied = 0;