linux-kernel - Re: [rfc] balance-on-fork NUMA placement

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Date:	Wed, 1 Aug 2007 02:21:14 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Andi Kleen <ak@...e.de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>
Subject: Re: [rfc] balance-on-fork NUMA placement

On Tue, Jul 31, 2007 at 10:01:14AM +0200, Ingo Molnar wrote:
> 
> * Nick Piggin <npiggin@...e.de> wrote:
> 
> > This patch uses memory policies to attempt to improve this. It 
> > requires that we ask the scheduler to suggest the child's new CPU 
> > earlier in the fork, but that is not a fundamental difference.
> 
> no fundamental objections, but i think we could simply move sched_fork() 
> to the following place:
> 
> > @@ -989,10 +990,13 @@ static struct task_struct *copy_process(
> >  	if (retval)
> >  		goto fork_out;
> >  
> > +	cpu = sched_fork_suggest_cpu(clone_flags);
> > +	mpol_arg = mpol_prefer_cpu_start(cpu);
> > +
> >  	retval = -ENOMEM;
> >  	p = dup_task_struct(current);
> >  	if (!p)
> > -		goto fork_out;
> > +		goto fork_mpol;
> >  
> >  	rt_mutex_init_task(p);
> 
> 
> _after_ the dup_task_struct(). Then change sched_fork() to return a CPU 
> number - hence we dont have a separate sched_fork_suggest_cpu() 
> initialization function, only one, obvious sched_fork() function. 
> Agreed?

That puts task struct, kernel stack, thread info on the wrong node.

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