linux-kernel - Re: [RFC][PATCH 14/16] writeback: move bdi threads exiting logic to the forker thread

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Date:	Tue, 20 Jul 2010 15:54:26 +0300
From:	Artem Bityutskiy <dedekind1@...il.com>
To:	Christoph Hellwig <hch@...radead.org>
Cc:	Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH 14/16] writeback: move bdi threads exiting logic
 to the forker thread

On Sun, 2010-07-18 at 03:02 -0400, Christoph Hellwig wrote:
> Yes, only killing threads from the caller is much better, that's how
> the kthread API is supposed to be used anyway.
> 
> >  static void bdi_queue_work(struct backing_dev_info *bdi,
> >  		struct wb_writeback_work *work)
> >  {
> > +	bool wakeup_default = false;
> > +
> >  	trace_writeback_queue(bdi, work);
> >  
> >  	spin_lock(&bdi->wb_lock);
> >  	list_add_tail(&work->list, &bdi->work_list);
> > -	spin_unlock(&bdi->wb_lock);
> > -
> >  	/*
> >  	 * If the default thread isn't there, make sure we add it. When
> >  	 * it gets created and wakes up, we'll run this work.
> >  	 */
> > -	if (unlikely(!bdi->wb.task)) {
> > +	if (unlikely(!bdi->wb.task))
> > +		wakeup_default = true;
> > +	else
> > +		wake_up_process(bdi->wb.task);
> > +	spin_unlock(&bdi->wb_lock);
> > +
> > +	if (wakeup_default) {
> >  		trace_writeback_nothread(bdi, work);
> >  		wake_up_process(default_backing_dev_info.wb.task);
> 
> Why not simply do the defaul thread wakeup under wb_lock, too?
> It keeps the code a lot simpler, and this is not a typical path anyway.

Hmm, actually, I want to take this lock in __mark_inode_dirty() as well,
so it makes sense to micro-optimize this. Also, can
'trace_writeback_nothread()' be called under a spinlock? If no, then a
variable is needed anyway.


-- 
Best Regards,
Artem Bityutskiy (Артём Битюцкий)

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