linux-kernel - Re: [patch for-3.14] mm, mempolicy: fix mempolicy printing in numa

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Date:	Tue, 28 Jan 2014 08:57:53 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Rik van Riel <riel@...hat.com>, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [patch for-3.14] mm, mempolicy: fix mempolicy printing in
 numa_maps

On Mon, Jan 27, 2014 at 03:31:32PM -0800, David Rientjes wrote:
> On Mon, 27 Jan 2014, Mel Gorman wrote:
> 
> > diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> > index c2ccec0..c1a2573 100644
> > --- a/mm/mempolicy.c
> > +++ b/mm/mempolicy.c
> > @@ -120,6 +120,14 @@ static struct mempolicy default_policy = {
> >  
> >  static struct mempolicy preferred_node_policy[MAX_NUMNODES];
> >  
> > +/* Returns true if the policy is the default policy */
> > +static bool mpol_is_default(struct mempolicy *pol)
> > +{
> > +	return !pol ||
> > +		pol == &default_policy ||
> > +		pol == &preferred_node_policy[numa_node_id()];
> > +}
> > +
> >  static struct mempolicy *get_task_policy(struct task_struct *p)
> >  {
> >  	struct mempolicy *pol = p->mempolicy;
> 
> I was trying to avoid doing this because numa_node_id() of process A 
> reading numa_maps for process B has nothing to do with the policy of the 
> process A and I thought MPOL_F_MORON's purpose was exactly for what it is 
> used for today. It works today since you initialize preferred_node_policy 
> for all nodes, but could this ever change to only be valid for N_MEMORY 
> node states, for example?
> 

You're right about the numa_node_id() usage, I should have called
task_node(p) to read the node it's currently running but that is potentially
obscure for different reasons.

> I'm not sure what the harm in updating mpol_to_str() would be if 
> MPOL_F_MORON is to change in the future?

It just has to be caught correctly and handled and it's a little non-obvious
but ok if I see a patch that modifies how MPOL_F_MORON is used in the
future I should remember to check for this.  I withdraw my objection for
your patch so

Acked-by: Mel Gorman <mgorman@...e.de>

-- 
Mel Gorman
SUSE Labs
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