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

From	Jan Kara <jack@suse.cz>
Newsgroups	linux.kernel
Subject	Re: [PATCH 4/9] writeback: track if we're sleeping on progress in balance_dirty_pages()
Date	2016-04-13 15:10 +0200
Message-ID	<rnsIr-1Gg-23@gated-at.bofh.it> (permalink)
References	<ripUS-7fj-3@gated-at.bofh.it> <riq4x-7jq-9@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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
-- 
Jan Kara <jack@suse.com>
SUSE Labs, CR

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Re: [PATCH 4/9] writeback: track if we're sleeping on progress in  balance_dirty_pages() Jan Kara <jack@suse.cz> - 2016-04-13 15:10 +0200
  Re: [PATCH 4/9] writeback: track if we're sleeping on progress in  balance_dirty_pages() Jens Axboe <axboe@fb.com> - 2016-04-13 16:30 +0200

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