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.
--
Jens Axboe
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