linux-kernel - Re: [PATCHv2 11/11] writeback: prevent unnecessary bdi threads wakeups

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Date:	Thu, 22 Jul 2010 05:00:23 -0400
From:	Christoph Hellwig <hch@...radead.org>
To:	Dave Chinner <david@...morbit.com>
Cc:	Artem Bityutskiy <dedekind1@...il.com>,
	Dave Chinner <dchinner@...hat.com>,
	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org,
	Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCHv2 11/11] writeback: prevent unnecessary bdi threads
 wakeups

On Thu, Jul 22, 2010 at 10:41:55AM +1000, Dave Chinner wrote:
> 	if (wakeup_bdi) {
> 		trace_writeback_wakeup(bdi)
> 		spin_lock(&bdi->wb_lock);
> 		if (!bdi->wb.task) {{
> 			trace_writeback_wakeup_nothread(bdi);
> 			wake_up_process(default_backing_dev_info.wb.task);
> 		} else
> 			wake_up_process(bdi->wb.task);
> 		spin_unlock(&bdi->wb_lock);

That gives us duplicate traces for the first case, what about:

	 if (wakeup_bdi) {
	 	spin_lock(&bdi->wb_lock);
		if (bdi->wb.task) {
			trace_writeback_wake_thread(bdi);
			wake_up_process(bdi->wb.task);
		} else {
			trace_writeback_wake_forker_thread(bdi);
			wake_up_process(default_backing_dev_info.wb.task);
		}
		spin_unlock(&bdi->wb_lock);
	}

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