linux-kernel - Re: [PATCH v4 2/2] virtio_balloon: Use a workqueue instead of "vballoon" kthread

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Message-ID: <20160102114316.GC3660@htj.duckdns.org>
Date:	Sat, 2 Jan 2016 06:43:16 -0500
From:	Tejun Heo <tj@...nel.org>
To:	"Michael S. Tsirkin" <mst@...hat.com>
Cc:	Petr Mladek <pmladek@...e.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeff Epler <jepler@...ythonic.net>,
	Jiri Kosina <jkosina@...e.cz>,
	virtualization@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, Petr Mladek <pmladek@...e.cz>
Subject: Re: [PATCH v4 2/2] virtio_balloon: Use a workqueue instead of
 "vballoon" kthread

Hello,

On Fri, Jan 01, 2016 at 12:18:17PM +0200, Michael S. Tsirkin wrote:
> > My initial idea was to use a dedicated workqueue. Michael S. Tsirkin
> > suggested using a system one. Tejun Heo confirmed that the system
> > workqueue has a pretty high concurrency level (256) by default.
> > Therefore we need not be afraid of too long blocking.
> 
> Right but fill has a 1/5 second sleep on failure - *that*
> is problematic for a system queue.

Why so?  As long as the maximum concurrently used workers are not
high, 1/5 second or even a lot longer sleeps are completely fine.

> > @@ -563,7 +534,7 @@ static void virtballoon_remove(struct virtio_device *vdev)
> >  	struct virtio_balloon *vb = vdev->priv;
> >  
> >  	unregister_oom_notifier(&vb->nb);
> > -	kthread_stop(vb->thread);
> > +	cancel_work_sync(&vb->wq_work);
> 
> OK but since job requeues itself, cancelling like this might not be enough.

As long as there's no further external queueing, cancel_work_sync() is
guaranteed to kill a self-requeueing work item.

Thanks.

-- 
tejun
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