Date: Tue, 27 Jan 2009 13:43:07 +0100
From: Ingo Molnar <mingo@elte.hu>
To: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Alasdair G Kergon <agk@redhat.com>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>,
       Lai Jiangshan <laijs@cn.fujitsu.com>,
       Peter Zijlstra <a.p.zijlstra@chello.nl>,
       Steven Rostedt <rostedt@goodmis.org>
Subject: Re: [RFC][PATCH] create workqueue threads only when needed
Message-ID: <20090127124307.GA12788@elte.hu>
References: <20090127001708.GA4815@nowhere> <20090127030727.GA15101@agk.fab.redhat.com> <20090127085738.GB5498@nowhere>
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* Frederic Weisbecker <fweisbec@gmail.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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