linux-kernel - Re: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1]

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Message-ID: <20060921072908.GA27280@elte.hu>
Date:	Thu, 21 Sep 2006 09:29:08 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Bill Huey <billh@...ppy.monkey.org>
Cc:	linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
	John Stultz <johnstul@...ibm.com>,
	"Paul E. McKenney" <paulmck@...ibm.com>,
	Dipankar Sarma <dipankar@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Esben Nielsen <simlo@...s.au.dk>
Subject: Re: [PATCH] move put_task_struct() reaping into a thread [Re: 2.6.18-rt1]


* Bill Huey <billh@...ppy.monkey.org> wrote:

> > but it _is_ already being reaped in another thread: softirq-rcu. 
> > Splitting that up any further will only fragment the 
> > context-switching and increases cache footprint - it wont (or 
> > rather, shouldnt) have any functional effect. (As a sidenote, i'm 
> > considering the unification of all 'same default priority' softirq 
> > threads into a single thread per CPU, to further reduce this cost of 
> > 'spreadout'.)
> 
> I overloaded another reaping thread that was doing largely similar 
> functionality in that it was also reaping, so I don't think it's that 
> bad. I did it from a cleanliness point of view with the code tree. 
> It's the "desched_thread" in fork.c that I'm using. It seems to be the 
> right thing to do. I'm sure Esben will follow up on this.

the reason why i added desched_thread was not because it's "more right" 
to do this from a separate context, but simply because the resource 
freed by it is not being freed via RCU by the upstream kernel. If that 
resource (mm_struct) were freed by RCU we'd have its rt-friendly 
reapdown "for free" and no desched_thread would be needed at all.

	Ingo
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