linux-kernel - Re: [2.6.24 regression][BUGFIX] numactl --interleave=all doesn't works on memoryless node.

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Date:	Wed, 06 Feb 2008 11:00:17 -0500
From:	Lee Schermerhorn <Lee.Schermerhorn@...com>
To:	Christoph Lameter <clameter@....com>
Cc:	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Paul Jackson <pj@....com>,
	David Rientjes <rientjes@...gle.com>,
	Mel Gorman <mel@....ul.ie>, torvalds@...ux-foundation.org,
	Eric Whitney <eric.whitney@...com>
Subject: Re: [2.6.24 regression][BUGFIX] numactl --interleave=all doesn't
	works on memoryless node.

On Tue, 2008-02-05 at 14:12 -0800, Christoph Lameter wrote:
> On Tue, 5 Feb 2008, Lee Schermerhorn wrote:
> 
> > mbind(2), on the other hand, just masks off any nodes in the 
> > nodemask that are not included in the caller's mems_allowed.
> 
> Ok so we temporarily adopt these semantics for set_mempolicy.
> 
> > 1) modify contextualize_policy to just remove the non-allowed
> >    nodes, as is currently done in-line for mbind().  This
> >    guarantees that the resulting mask includes only nodes with
> >    memory.
> 
> Right make ssense. we already contextualize for cpusets.

Only for mbind().  set_mempolicy(), via contextualize_policy() was just
returning EINVAL for invalid nodes in the mask.  I don't know if it
always worked like this, or if we did this in the memoryless nodes
series...

> 
> > Index: Linux/mm/mempolicy.c
> > ===================================================================
> > --- Linux.orig/mm/mempolicy.c	2008-02-05 11:25:17.000000000 -0500
> > +++ Linux/mm/mempolicy.c	2008-02-05 16:03:11.000000000 -0500
> > @@ -131,7 +131,7 @@ static int mpol_check_policy(int mode, n
> >  			return -EINVAL;
> >  		break;
> >  	}
> > - 	return nodes_subset(*nodes, node_states[N_HIGH_MEMORY]) ? 0 : -EINVAL;
> > + 	return 0;
> >  }
> 
> Hmmm... That is a pretty drastic change.

the nodes_subset() would always return true, once we mask it with
cpuset_current_mems_allowed(), right?  mems_allowed can now only contain
nodes with memory and if cpusets are not configured,
cpuset_current_mems_allowed() just returns node_states[N_HIGH_MEMORY].

So, I think this is a no-op.

> 
> > @@ -188,8 +188,6 @@ static struct mempolicy *mpol_new(int mo
> >  	switch (mode) {
> >  	case MPOL_INTERLEAVE:
> >  		policy->v.nodes = *nodes;
> > -		nodes_and(policy->v.nodes, policy->v.nodes,
> > -					node_states[N_HIGH_MEMORY]);
> >  		if (nodes_weight(policy->v.nodes) == 0) {
> >  			kmem_cache_free(policy_cache, policy);
> >  			return ERR_PTR(-EINVAL);
> 
> Do we really need to remove these lines if we change set_mempolicy?

Again, with the change to contextualize_policy(), the nodemask is
guaranteed to only contain nodes with memory, so this was redundant.

> 
> > @@ -426,9 +424,13 @@ static int contextualize_policy(int mode
> >  	if (!nodes)
> >  		return 0;
> >  
> > +	/*
> > +	 * Restrict the nodes to the allowed nodes in the cpuset.
> > +	 * This is guaranteed to be a subset of nodes with memory.
> > +	 */
> >  	cpuset_update_task_memory_state();
> > -	if (!cpuset_nodes_subset_current_mems_allowed(*nodes))
> > -		return -EINVAL;
> > +	nodes_and(*nodes, *nodes, cpuset_current_mems_allowed);
> > +
> >  	return mpol_check_policy(mode, nodes);
> >  }
> >  
> 
> Ditto?

This is the main change in the patch:  masking off the invalid nodes
[like sys_mbind() did inline] rather than complaining about them.

However, after I finish testing, I will post an update to this patch
which restores some of the error checks that this change lost.

> 
> > @@ -797,7 +799,7 @@ static long do_mbind(unsigned long start
> >  	if (end == start)
> >  		return 0;
> >  
> > -	if (mpol_check_policy(mode, nmask))
> > +	if (contextualize_policy(mode, nmask))
> >  		return -EINVAL;
> >  
> >  	new = mpol_new(mode, nmask);
> > @@ -915,10 +917,6 @@ asmlinkage long sys_mbind(unsigned long 
> >  	err = get_nodes(&nodes, nmask, maxnode);
> >  	if (err)
> >  		return err;
> > -#ifdef CONFIG_CPUSETS
> > -	/* Restrict the nodes to the allowed nodes in the cpuset */
> > -	nodes_and(nodes, nodes, current->mems_allowed);
> > -#endif
> 
> Would just removing #ifdef CONFIG_CPUSETS work? mems_allowed falls back to 
> node_possible_map.... Shouldnt that be node_online_map?

I removed this because I changed do_mbind() to call the revised
contextualize_policy() that does exactly this masking.  I didn't see any
reason to leave the duplicate code there.

I think that mems_allowed now falls back to nodes with memory.  Or it
should in the current code.  When Paul adds his new magic, that might
change.

Lee
> 

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