linux-kernel - Re: [RFC][PATCH] create workqueue threads only when needed

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Message-ID: <20090127124307.GA12788@elte.hu>
Date:	Tue, 27 Jan 2009 13:43:07 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Frederic Weisbecker <fweisbec@...il.com>
Cc:	Alasdair G Kergon <agk@...hat.com>, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Steven Rostedt <rostedt@...dmis.org>
Subject: Re: [RFC][PATCH] create workqueue threads only when needed


* Frederic Weisbecker <fweisbec@...il.com> wrote:

> On Tue, Jan 27, 2009 at 03:07:27AM +0000, Alasdair G Kergon wrote:
> > On Tue, Jan 27, 2009 at 01:17:11AM +0100, Frederic Weisbecker wrote:
> > > For several reasons:
> > > _ Unneeded built drivers for my system that create workqueue(s) when they init
> > > _ Services which need their own workqueue, for several reasons, but who receive
> > >   very rare jobs (often never)
> > 
> > > I hadn't any problems until now with this patch but I think it needs more testing,
> > > like with cpu hotplug, and some renaming for its functions and structures...
> > > And I would like to receive some comments and feelings before continuing. So this
> > > is just an RFC :-)
> > 
> > Make sure this optimisation also works when the system's running low 
> > on memory if workqueues are involved in "making forward progress".  
> > Doubtless there are other reasons for apparently-unused workqueues 
> > too.
> 
> That's true. But currently, each useless workqueue thread is consuming a 
> task_struct in memory, so this patch makes actually consuming less 
> memory than before. If the system is running low on memory...well 
> perhaps I can reschedule the thread creation after some delays...?

Lets put a warning in there to make sure it's not forgotten - and deal 
with it if it happens.

	Ingo
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