Messages in this thread | | | Subject | Re: [PATCH 4/9] writeback: track if we're sleeping on progress in balance_dirty_pages() | From | Jens Axboe <> | Date | Wed, 13 Apr 2016 08:20:09 -0600 |
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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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