linux-kernel - Re: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate lazy RCU callbacks

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Message-ID: <20120906174112.GL2448@linux.vnet.ibm.com>
Date:	Thu, 6 Sep 2012 10:41:12 -0700
From:	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linux-kernel@...r.kernel.org, mingo@...e.hu, laijs@...fujitsu.com,
	dipankar@...ibm.com, akpm@...ux-foundation.org,
	mathieu.desnoyers@...ymtl.ca, josh@...htriplett.org,
	niv@...ibm.com, tglx@...utronix.de, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, eric.dumazet@...il.com, darren@...art.com,
	fweisbec@...il.com, sbw@....edu, patches@...aro.org,
	"Paul E. McKenney" <paul.mckenney@...aro.org>
Subject: Re: [PATCH tip/core/rcu 07/23] rcu: Provide OOM handler to motivate
 lazy RCU callbacks

On Thu, Sep 06, 2012 at 09:52:53AM -0400, Steven Rostedt wrote:
> On Thu, 2012-09-06 at 15:46 +0200, Peter Zijlstra wrote:
> > On Thu, 2012-08-30 at 11:18 -0700, Paul E. McKenney wrote:
> > > +       get_online_cpus();
> > > +       for_each_online_cpu(cpu)
> > > +               for_each_rcu_flavor(rsp)
> > > +                       smp_call_function_single(cpu, rcu_oom_notify_cpu,
> > > +                                                rsp, 1);
> > > +       put_online_cpus(); 
> > 
> > I guess blasting IPIs around is better than OOM but still.. do you
> > really need to wait for each cpu individually, or would a construct
> > using on_each_cpu() be possible, or better yet, on_each_cpu_cond()?

I rejected on_each_cpu_cond() because it disables preemption across
a scan of all CPUs.  Probably need to fix that at some point...

> Also, what about having the rcu_oom_notify_cpu handler do the
> for_each_rcu_flavor() and not send an IPI multiple times to a single
> CPU?

Fair enough!

							Thanx, Paul

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